oversight

Manufactured Housing Standards: Testing and Performance Evaluation Could Better Ensure Safe Indoor Air Quality

Published by the Government Accountability Office on 2012-10-24.

Below is a raw (and likely hideous) rendition of the original report. (PDF)

               United States Government Accountability Office

GAO            Report to Congressional Requesters




October 2012
               MANUFACTURED
               HOUSING
               STANDARDS
               Testing and
               Performance
               Evaluation Could
               Better Ensure Safe
               Indoor Air Quality




GAO-13-52
                                               October 2012

                                               MANUFACTURED HOUSING STANDARDS
                                               Testing and Performance Evaluation Could Better
                                               Ensure Safe Indoor Air Quality
Highlights of GAO-13-52, a report to
congressional requesters




Why GAO Did This Study                         What GAO Found
Since 1976, HUD has been                       Key standards for manufactured homes provide a lower margin of safety against
responsible for developing construction        a carbon monoxide exposure incident than those for site-built homes, which are
and safety standards (the HUD Code)            constructed at their permanent locations. For instance, the Department of
for manufactured homes. Concerns               Housing and Urban Development (HUD) Code requires a minimum 3-foot
have been raised by Congress and               separation between air intakes and exhaust vents, while industry standards for
others about existing HUD code                 site-built homes have required a greater distance for many years. The industry
requirements that are intended to              standards call for a greater separation between air intakes and exhaust vents to
ensure proper indoor air quality,              help reduce the risk that contaminants such as carbon monoxide will re-enter the
including protecting occupants from
                                               home. Indoor air quality experts whom GAO interviewed stated that the exhaust
potential carbon monoxide exposure.
                                               of an improperly operating furnace combined with unique wind conditions could,
As requested, GAO examined
1) existing standards for separating air
                                               in rare cases, present a risk of carbon monoxide exposure. GAO analysis shows
intakes and exhaust vents in both              that increasing the separation between an air intake and exhaust vents, using
manufactured and site-built homes;             industry standards, can significantly dilute concentrations of contaminants.
2) reasons for differences in ventilation      The primary reason for the differences in ventilation standards for manufactured
standards for manufactured and site-           homes and site-built homes is the HUD Code has not been updated since 2005
built homes; and 3) the number of              and has not kept pace with standards tied to ventilation and air quality for site-
manufactured homes built, the                  built homes. For example, updates to standards for site-built homes made in
distances between their air intakes and
                                               2003 requiring a greater separation between intakes and exhaust vents are only
exhaust vents, and the performance of
                                               now being considered by HUD for manufactured homes. This update was
their ventilation systems. GAO
reviewed documentation from HUD                recommended to HUD in 2010 by the Manufactured Housing Consensus
and building standards organizations to        Committee (MHCC), which is responsible for recommending proposed rule
determine differences in requirements          changes to HUD. Similarly, requirements for carbon monoxide detectors adopted
tied to ventilation and air quality,           in industry standards for site-built homes and recommended by the MHCC in
reviewed the rulemaking process and            2009 have yet to be incorporated in the HUD Code. HUD did publish a proposed
status of proposed updates to                  rule in the Federal Register in 2010 to update aspects of the HUD Code but has
manufactured housing standards                 not issued a final rule because the rulemaking process is ongoing. Additional
related to ventilation and air quality,        proposals, including the two above related to indoor air quality, are under
analyzed data on the occupancy of              consideration by HUD, but have not yet been published as proposed rules.
manufactured houses subject to HUD’s
standards, assessed HUD’s efforts to           An estimated 5.5 million occupied manufactured homes were built under the
ensure compliance with certain                 HUD Code, according to 2009 American Housing Survey data. Although HUD
standards, and interviewed agency              retains copies of approved designs of manufactured homes, the agency does not
officials and indoor air quality experts.      maintain data on the actual distances between the air intakes and exhaust vents
                                               of each home. Further, once ventilation systems are installed in manufactured
What GAO Recommends                            homes, HUD does not require manufacturers to test their performance. For
GAO recommends that HUD test the               example, manufacturers are not required to determine if the systems meet the
performance of installed ventilation           requirements for the whole-house ventilation airflow rate, which quantifies the
systems and reassess its ventilation           volume of air exchanged in the home over time. Without performance testing of
standards. HUD generally agreed with           the installed ventilation systems, HUD cannot fully ensure that the systems
both recommendations and stated that           installed in manufactured homes are meeting performance specifications. In
it would bring them before the MHCC            addition, HUD’s standard for the whole-house airflow rate provided by
for consideration.                             mechanical ventilation was initially established assuming a certain level of natural
                                               air infiltration. This whole-house airflow rate standard has not changed since
                                               1993. Air quality experts and research suggest that homes are increasingly being
                                               built with less air leakage, reducing the expected level of natural air infiltration.
View GAO-13-52. For more information,
contact Mathew J. Scirè at (202) 512-8678 or   However, HUD has not reassessed the whole-house ventilation airflow rate
sciremj@gao.gov.                               standard to determine whether it continues to be sufficient to assure adequate air
                                               quality.
                                                                                        United States Government Accountability Office
Contents


Letter                                                                                     1
               Scope and Methodology                                                       2
               Background                                                                  3
               Ventilation and Air Quality Standards Differ between Manufactured
                 and Site-Built Homes                                                      7
               Updates to the HUD Code on Key Standards Related to Ventilation
                 and Air Quality Lag behind Industry Standards for Site-Built
                 Homes                                                                   11
               Millions of Manufactured Homes Have Been Built under the HUD
                 Code but HUD Has Not Tested the Performance of Installed
                 Ventilation Systems                                                     15
               Conclusions                                                               18
               Recommendations for Executive Action                                      20
               Agency Comments and Our Evaluation                                        20

Appendix I     Comparison of Different Separation Distances Between Air Intakes
               and Exhaust Vents and Impacts on Potential Carbon Monoxide
               Exposure                                                                  23



Appendix II    Comments from the Department of Housing and Urban Development             27



Appendix III   GAO Contact and Staff Acknowledgements                                    29



Table
               Table 1: Parameters Used in Our Analysis                                  25


Figures
               Figure 1: HUD Label                                                         5
               Figure 2: HUD Code’s Separation Requirement for Fresh Air
                        Intakes and Exhaust Vents, 2012                                    7
               Figure 3: Air Intake Contaminant Concentration at Different Wind
                        Speds for Various Exhaust Vent to Air Intake Separations           9
               Figure 4: GAO Analysis of HUD Processes for Updating the HUD
                        Code                                                             12



               Page i                                GAO-13-52 Manufactured Housing Standards
Figure 5: Contaminant Concentration at Air Intake for Different
         Wind Speeds and Various Exhaust Vent to Air Intake
         Separations                                                                      26




This is a work of the U.S. government and is not subject to copyright protection in the
United States. The published product may be reproduced and distributed in its entirety
without further permission from GAO. However, because this work may contain
copyrighted images or other material, permission from the copyright holder may be
necessary if you wish to reproduce this material separately.




Page ii                                        GAO-13-52 Manufactured Housing Standards
United States Government Accountability Office
Washington, DC 20548




                                   October 24, 2012

                                   The Honorable James P. Moran
                                   Ranking Member
                                   Subcommittee on Interior, Environment, and Related Agencies
                                   Committee on Appropriations
                                   House of Representatives

                                   The Honorable John W. Olver
                                   Ranking Member
                                   Subcommittee on Transportation, Housing, and Urban Development,
                                    and Related Agencies
                                   Committee on Appropriations
                                   House of Representatives

                                   The Department of Housing and Urban Development (HUD) certified
                                   manufactured homes offer a lower-cost option to traditional site-built
                                   homes. In 2010, an estimated 18 million individuals lived in manufactured
                                   homes, which are defined as transportable structures of at least 320
                                   square feet built on permanent chassis structures. 1 Since 1976, all
                                   manufactured homes (formerly called “mobile homes”) have been
                                   required to meet HUD’s Manufactured Home Construction and Safety
                                   Standards (the HUD Code), the only building code that preempts state
                                   and local building codes. The HUD Code covers body and frame
                                   requirements, thermal protection, plumbing, electrical, ventilation, and
                                   other aspects of the home. Every home built to the HUD Code is
                                   identified with a red metal tag, known as the HUD certification label.

                                   In your request, you raised concerns that the HUD Code’s ventilation
                                   standards, particularly the separation distance between fresh air intakes
                                   and exhaust vents that is intended to assure that contaminants do not
                                   reenter a home, may not be keeping pace with standards for site-built
                                   homes. For this review, we examined 1) existing standards for separating
                                   air intakes and exhaust vents in both manufactured and site-built homes;
                                   2) reasons for differences in ventilation standards for manufactured and
                                   site-built homes; and 3) the number of HUD manufactured homes built,



                                   1
                                    This estimate is from the U.S. Census Bureau’s 2010 American Community Survey
                                   (ACS). The margins of error for these estimates are +/- 87,000.




                                   Page 1                                     GAO-13-52 Manufactured Housing Standards
              including the distances between their air intakes and exhaust vents, and
              the performance of their ventilation systems.


              To examine standards associated with the separation distance between
Scope and     air intakes and exhaust vents in homes, we collected and analyzed
Methodology   information on existing standards for home ventilation systems.
              Specifically, we collected and analyzed documentary information on
              construction and safety standards for manufactured homes and
              interviewed representatives from HUD to ascertain how such standards
              were developed. Likewise, we collected information on commonly-
              accepted industry standards for site-built homes and the evolution of
              those standards. We also interviewed subject area experts performing
              research on ventilation and air quality issues for manufactured homes to
              understand factors affecting the indoor air quality of manufactured and
              site-built homes. Further, we contacted state administrative agency
              officials in 5 of the 37 states that administer manufactured housing
              consumer programs for information on indoor air quality complaints. We
              chose administrative agencies in New York, Pennsylvania, Tennessee
              and Texas based on different climate zones and numbers of placed
              manufactured homes. We added Utah because carbon monoxide
              poisoning had allegedly occurred in a manufactured home. We selected
              states with relatively high numbers of manufactured homes, using data
              from the Census Bureau’s 2010 Manufactured Homes Survey.
              Additionally, we compared different separation distances between air
              intakes and exhaust vents and the potential for carbon monoxide
              exposure using modeling methods from the American Society of Heating,
              Refrigerating, and Air-Conditioning Engineers (ASHRAE). Appendix I
              contains a more detailed description of our comparison.

              To assess the rationale for having different ventilation standards for
              manufactured and site-built homes, we collected documentary information
              and contacted officials from HUD, industry associations, and
              organizations that set building standards. Specifically, we identified the
              reasons behind the differences in ventilation standards for manufactured
              versus site-built homes, the evolution of these standards over time, and
              the current status of new or revised standards that have been proposed
              for manufactured homes.

              To determine the number of manufactured homes that have been built to
              HUD standards, we analyzed U.S. Census Bureau estimates on the
              number of occupied manufactured homes built since 1975 and relevant
              characteristics of the homes. We assessed the reliability of the Census


              Page 2                                GAO-13-52 Manufactured Housing Standards
                     Bureau’s 2009 American Housing Survey and 2010 American Community
                     Survey by reviewing information on the data and interviewing
                     knowledgeable officials on the quality of the data. We determined the
                     data were sufficiently reliable for the purposes of this report. To identify
                     and obtain available data on the design and performance of ventilation
                     systems in manufactured homes, we sought information from HUD on the
                     distances between intake and exhaust vents and the performance of the
                     ventilation systems. We also contacted officials from industry
                     associations, researchers, and companies in the manufactured home
                     industry to identify common design and performance specifications that
                     they used for manufactured homes. Further, we collected information
                     from organizations that conduct testing and certify ventilation systems for
                     manufactured homes.

                     We conducted this performance audit from December 2011 through
                     October 2012 in accordance with generally accepted government auditing
                     standards. Those standards require that we plan and perform the audit to
                     obtain sufficient, appropriate evidence to provide a reasonable basis for
                     our findings and conclusions based on our audit objectives. We believe
                     that the evidence obtained provides a reasonable basis for our findings
                     and conclusions based on our audit objectives.



Background
HUD Oversight and    HUD is responsible for enforcing the federal manufactured home
Standards for        construction and safety standards that it established under The National
Manufactured Homes   Manufactured Housing Construction and Safety Standards Act of 1974. 2
                     The act authorized HUD to develop construction and safety standards for
                     manufactured homes and to oversee the enforcement of the standards
                     through inspections and review of building plans. HUD developed the
                     Manufactured Housing Construction and Safety Standards, commonly
                     known as the HUD Code, basing them in substantial part on the National




                     2
                     Pub. L. No. 93-383, Title VI.




                     Page 3                                 GAO-13-52 Manufactured Housing Standards
Fire Protection Association (NFPA) standards for manufactured homes
(NFPA 501). 3 The HUD Code was implemented in 1976. 4

Because a manufactured home can be moved from one state to another,
the HUD Code is applied nationwide and preempts state and local codes.
As a result, state and local building authorities may not apply their own
codes to manufactured homes for components covered by the HUD
Code, such as ventilation systems. Unlike site-built homes, which are
constructed at their permanent locations, manufactured homes are
constructed in factories and must have a permanent chassis so that they
can be moved on wheels to retailers or consumers in different states and
localities, where they are placed on temporary or permanent foundations.
Manufactured homes differ from modular homes, which are another type
of prefabricated home and are often designed and constructed by the
same manufacturers that construct manufactured homes. Like site-built
homes, modular homes are built to state and local building codes. But
unlike manufactured homes that are required to be moved to the site and
remain on wheeled chassis, modular home sections or modules are
transported on truck beds and assembled on site.

The 1974 act was amended by the Manufactured Housing Improvement
Act of 2000 to create a balanced consensus process for establishing and
revising manufactured home building standards. 5 The amendment
established the Manufactured Housing Consensus Committee (MHCC), a
federal advisory committee established to provide recommendations to
the HUD Secretary on new standards and revisions of current standards.

The MHCC consists of voting members representing seven producers or
retailers of manufactured housing; seven representatives of consumer
interests, such as owners of manufactured homes; and seven general
interest and public official members. In addition to construction and safety
standards, the MHCC also develops proposed model installation



3
 NFPA is a nonprofit organization that focuses on the prevention of fire and other hazards
through codes and standards, research, training, and education. First published in 1940,
NFPA 501 Standard for Manufactured Housing establishes minimum criteria for
manufactured homes and is updated periodically. The NFPA has a HUD contract to
provide administrative, managerial, and technical support to the MHCC.
4
24 C.F.R. Part 3280.
5
Pub. L. No. 106–569, Title VI.




Page 4                                        GAO-13-52 Manufactured Housing Standards
                             standards for the manufactured housing industry. Two-thirds of MHCC
                             members must approve a proposal before the committee recommends it
                             to HUD.

                             As part of the oversight of manufactured homes, HUD approves certain
                             state agencies and private third-party entities to inspect manufactured
                             housing plants and determine whether manufacturers are complying with
                             the HUD Code. Each manufacturer contracts with two types of third-party
                             entities, a Design Approval Primary Inspection Agency (DAPIA) and In-
                             plant Production Primary Inspection Agency (IPIA). DAPIAs review and
                             approve all home designs, design changes, and each plant’s quality
                             assurance manuals. To ensure that homes comply with the HUD Code,
                             manufacturers contract with IPIAs to approve and monitor their quality
                             control programs by inspecting each home at some stage of production in
                             the plant. IPIAs issue the HUD label that is attached to each section of
                             the home upon completion (see fig. 1).

                             Figure 1: HUD Label




Ventilation Standards Used   Builders of manufactured homes, as well as site-built and modular
for Manufactured Homes       homes, are designing more tightly constructed homes that have less
                             natural air infiltration in order to reduce energy costs for consumers.
                             Without proper ventilation, a home’s occupants may be exposed to a
                             buildup of harmful contaminants, such as carbon monoxide,



                             Page 5                                 GAO-13-52 Manufactured Housing Standards
formaldehyde, and mold. 6 In addition to the HUD Code, multiple federal
agencies have an interest in and have made efforts to improve indoor air
quality in buildings.

To prevent indoor contamination and compensate for less natural air in
manufactured homes, the HUD Code requires a whole-house ventilation
system consisting of either mechanical ventilation or systems combining
mechanical and passive ventilation. 7 Mechanical ventilation uses fans
and ducts to bring fresh air into the home or draw contaminated air to the
outdoors. Passive ventilation takes place naturally through windows,
doors, and other air leakage sites. One common mechanical ventilation
approach uses an outdoor air intake that is connected to the air
distribution system return duct and that carries fresh air into the home
whenever the furnace fan operates. Another approach uses a whole-
house exhaust fan, which draws contaminants from the home to the
outdoors. In both cases, the system releases air to the outdoors through
an exhaust vent, preventing the build-up of contaminants indoors.
Although mechanical ventilation is becoming more common, most older
site-built homes have relied on passive ventilation.

To help ensure that contaminants that accumulate indoors are adequately
vented out of the home and replaced with fresh outside air, the HUD
Code requires a certain whole-house ventilation airflow rate. This rate
specifies the volume of air that should be “replaced” over time—that is,
fresh air drawn into the ventilation system as contaminated air is expelled.
HUD requires an airflow rate of least 0.035 cubic feet per minute for each
square foot of interior floor space or its hourly average equivalent. The
ventilation system is required to produce between 50 and 90 cubic feet
per minute to achieve this whole-house airflow rate. 8




6
 Carbon monoxide is particularly hazardous because it is colorless, odorless, and
tasteless. According to Centers for Disease Control (CDC) estimates, from 1999 to 2004
an average of 439 persons died annually from unintentional, non-fire-related carbon
monoxide poisoning. CDC estimates from 2000 to 2009 show that about 78 percent
(53,039) of carbon monoxide exposure-related incidents occurred in the home.
7
24 C.F.R. § 3280.103(b)
8
24 C.F.R. § 3280.103(b).




Page 6                                       GAO-13-52 Manufactured Housing Standards
                      Standards exist for separating air intakes and exhaust vents in both
Ventilation and Air   manufactured and site-built homes, but standards for the two types of
Quality Standards     homes differ. Since 1976, HUD’s ventilation system specifications for
                      manufactured homes have required that any fresh air intake be at least 3
Differ between        feet from any exhaust vent—for example, from a gas furnace exhaust or
Manufactured and      plumbing system vent. (See fig. 2.)
Site-Built Homes
                      Figure 2: HUD Code’s Separation Requirement for Fresh Air Intakes and Exhaust
                      Vents, 2012




                      Compared with the HUD Code, industry standards commonly used for
                      site-built homes recommend a greater distance between air intakes and
                      exhaust vents. State and local building codes commonly cite generally
                      accepted ventilation standards from ASHRAE and the International
                      Residential Code (IRC). Specifically, ASHRAE requires a 10-foot
                      horizontal separation between any air intake and exhaust vent.
                      Additionally, IRC requires either a 10-foot horizontal separation or a
                      minimum vertical separation of 3 feet if the horizontal separation is less
                      than 10 feet.

                      Industry standards that address the separation distance between air
                      intakes and exhaust vents were created to reduce the possibility that
                      contaminants in the exhaust, such as carbon monoxide, would reenter the
                      building. Experts associated with testing and establishing ventilation



                      Page 7                                   GAO-13-52 Manufactured Housing Standards
standards said that increasing the distance between the air intakes and
exhaust vents would improve the margin of safety, making it less likely
that contaminants, such as carbon monoxide, could reenter the home.
Experts explained, however, that such an event would occur rarely and
would require a combination of several factors. They noted that the
exhaust of a properly functioning furnace would contain relatively low
levels of carbon monoxide (e.g. less than 4 parts per million (ppm)). They
also noted an improperly functioning furnace, however, could produce
hazardous carbon monoxide levels that, coupled with unique wind
conditions, could result in carbon monoxide gas reentering a home
through a fresh air intake. Because carbon monoxide is produced by
incomplete combustion in fuel-burning devices such as gas furnaces,
contamination is most likely in homes utilizing combustible fuels for
heating and with an outdoor air intake connected to the air distribution
duct system.

Our analysis of scenarios involving the dispersion of exhaust containing
carbon monoxide demonstrated that the contaminant was less likely to
reenter a building when the separation distance between an air intake
and exhaust vent was increased. Using calculations recommended by
ASHRAE, we quantified the difference in contaminant concentrations at
the air intake as a function of wind speeds for various exhaust vent to air
intake separations. As shown in figure 3, across a range of wind speeds,
contaminant concentrations at air intakes placed either 10 feet
horizontally or 3 feet horizontally and 3 feet vertically from an exhaust
vent are less than contaminant concentrations that would be expected at
an air intake separated just 3 feet horizontally (HUD Code requirement)
from an exhaust vent. The figure also shows that the effect of separation
distance on concentration levels is particularly evident at low wind
speeds. For example, in a light 1 mph wind, exhaust with a carbon
monoxide concentration of 200 parts per million (ppm) would be diluted to
approximately 50 ppm at an air intake separated 3 feet horizontally from
the exhaust vent. Increasing the separation between the exhaust vent
and air intake to either 10 feet horizontally or 3 feet horizontally and 3 feet
vertically in a 1 mph wind results in carbon monoxide concentrations of
less than 10 ppm at the air intake.




Page 8                                   GAO-13-52 Manufactured Housing Standards
Figure 3: Air Intake Contaminant Concentration at Different Wind Speds for Various Exhaust Vent to Air Intake Separations




                                         Note: The lines shown in the figure were generated using an exhaust-to-intake dilution calculation,
                                         based on recommendations from ASHRAE members, with parameters typically found in
                                         manufactured housing. Among the parameters used in our scenario, we assumed a capped exhaust
                                         vent with a diameter of 4 inches, which emitted exhaust at a speed of 1000 feet per minute, and
                                         which contained a CO concentration of 200 parts per million (ppm). The dilution levels determined by
                                         use of the calculation will vary based on changing these and other parameters. See Appendix I for a
                                         more detailed discussion of our use of the ASHRAE dilution equations.


                                         These results were consistent with statements made by indoor air quality
                                         experts that increasing the distance between air intakes and exhaust
                                         vents reduces the concentration of contaminants such as carbon
                                         monoxide from reentering a home.

                                         Concerns about the risk of carbon monoxide reentering the fresh air
                                         intake of a manufactured home were presented to the MHCC in July
                                         2009, including an explanation of the differences between current industry
                                         standards and the HUD Code. That is, the MHCC viewed a presentation
                                         prepared by an individual who claimed an incident of carbon monoxide
                                         reentering a home built to the existing HUD Code requiring a separation
                                         distance of 3 feet.

                                         HUD officials told us that the agency, in its oversight capacity for the
                                         Manufactured Housing Program, had not received any reports, other than
                                         the incident described above, either directly or from state administrative



                                         Page 9                                              GAO-13-52 Manufactured Housing Standards
agencies, on cases of carbon monoxide reentering manufactured homes
through fresh air intakes. We also contacted several state administrative
agencies in the five states we reviewed, all of which stated that they had
not received reports from consumers of any incidents of carbon monoxide
reentering a home through a fresh air intake. HUD has not conducted or
sponsored research to determine an appropriate separation distance
between the fresh air intakes and exhaust vents since the HUD Code was
established in 1976, according to HUD officials. However, HUD has
sponsored research related to whole-house ventilation that discusses
airflow rate issues.

Industry standards also call for carbon monoxide detectors in all site-built
and modular homes. These detectors are not intended to be used as a
measure of, or to test for, adequate indoor air quality but are a safety
device to warn occupants in the event of a dangerous build-up of carbon
monoxide gasses in the air. IRC and ASHRAE have required carbon
monoxide detectors for residential site-built and modular homes since
2009 and 2010, respectively. While the MHCC has recommended this
standard be required for all new manufactured homes, it is not yet a
requirement in the HUD Code.




Page 10                                GAO-13-52 Manufactured Housing Standards
                       As of April 2012, HUD officials stated they were reviewing 84 MHCC
Updates to the HUD     recommendations on changes to the HUD Code. However, time delays
Code on Key            associated with considering updates to the HUD Code continue to
                       exacerbate differences between standards for manufactured and site-built
Standards Related to   homes. These include MHCC recommendations and proposed changes
Ventilation and Air    related to ventilation and indoor air quality that HUD has begun
Quality Lag behind     considering to bring the HUD Code in line with industry standards.
                       However, HUD’s process for considering and approving proposed
Industry Standards     changes, which includes development and consideration of proposed
for Site-Built Homes   changes by the MHCC, can take many years (see fig. 4). Despite the
                       outstanding proposed changes that are being considered, HUD has not
                       adopted any changes to the HUD Code since 2005. Another set of
                       proposed updates to the HUD Code were published in the Federal
                       Register in 2010, and a final rule is currently under review at HUD,
                       according to HUD officials. Further, other proposed updates being
                       considered by HUD have not yet been published in the Federal Register
                       as proposed updates to the HUD Code. These include MHCC safety
                       designated items related to air quality and ventilation.




                       Page 11                              GAO-13-52 Manufactured Housing Standards
Figure 4: GAO Analysis of HUD Processes for Updating the HUD Code




                                      MHCC recommended in 2010 that HUD increase the separation distance
                                      between air intakes and exhaust vents. HUD officials said that HUD is
                                      now considering this recommendation to increase the separation distance
                                      toward industry standards, which were modified in 2003. The
                                      requirements for this separation distance in the HUD Code have
                                      remained unchanged since 1976, when HUD first established the HUD
                                      Code. We found that IRC and ASHRAE standards on ventilation were
                                      periodically updated about every 3 years.




                                      Page 12                             GAO-13-52 Manufactured Housing Standards
Specifically, in the 2003 version of its residential ventilation standards,
ASHRAE stated several reasons for the need to update the standards,
including:

•   recognition by government agencies on ties between indoor air quality
    and health effects;
•   increasingly more energy-efficient, air-tight homes being constructed;
•   increased concerns over residential indoor air quality and ventilation;
    and
•   the importance of adequate whole-house ventilation to improve air
    quality.

According to HUD officials, HUD is currently considering the MHCC
recommendation to increase the distance between the air intakes and
exhaust vents to a 3-foot vertical separation if the horizontal distance is
less than 10 feet. MHCC developed the proposal after hearing the public
testimony in July 2009 alleging that exhaust from a vent reentered a
manufactured home through the air intake and caused carbon monoxide
poisoning. MHCC made the recommendation to HUD in April 2010, but as
of August 2012, HUD had not published a proposed rule in the Federal
Register. A HUD official explained that HUD had received and is
considering the MHCC recommendation to revise the current separation
distance required between air intakes and exhaust vents. That is, HUD
has not completed its internal clearance process – step 4 in figure 4.

HUD is also considering an MHCC recommendation to require installation
of carbon monoxide detectors for all new manufactured homes. MHCC
made this recommendation in December 2009. Similarly, HUD officials
stated that HUD has not completed the economic analysis or drafted the
proposed rule for this recommendation. As we have seen, other
organizations that set industry standards already have this requirement—
the IRC since 2009 and ASHRAE since 2010.

The Manufactured Housing Improvement Act of 2000 established a 1-
year time limit for HUD to publish decisions on MHCC recommendations
in the Federal Register. 9 HUD’s website states that statutory language




9
 Pub. L. No. 106-569 requires the Secretary of HUD to either accept, reject, or modify
proposed changes to the HUD Code within 1 year and publishing the decisions for
notification or further comment in the Federal Register.




Page 13                                        GAO-13-52 Manufactured Housing Standards
requiring the MHCC to submit recommendations to HUD in the form of a
proposed rule, including an economic analysis, is impractical.

HUD explains that the MHCC does not have the technical expertise to
present HUD with a rule package that meets the requirements of the
Federal Register and the Administrative Procedure Act. HUD collects the
necessary supporting information and then prepares the proposed rule.
According to HUD, proposals that the MHCC recommends are then
subject to a review and clearance process—which can be lengthy—first
within HUD and then are subject to review and approval by the Office of
Management and Budget. We plan to assess these rulemaking issues,
including options for accelerating the process, in future work.

We also observed several administrative challenges facing the
Manufactured Housing Program. For example, NFPA temporarily
suspended its administration of the MHCC in May 2012, citing that HUD
had not yet paid invoices supporting the committee. Later, NFPA officials
stated they had resumed the function for administering the MHCC after
HUD paid the outstanding funds due. Further, MHCC members we spoke
to told us that HUD’s Office of Manufactured Housing was understaffed
and lacking in resources, possibly contributing to delays in updating the
standards. HUD officials stated that the Manufactured Housing Program
and its processes can be labor intensive. The program has 10 authorized
staff positions. The office has been run by an Acting Deputy Administrator
since July 2011. The Administrator position has been vacant since 2010.

Industry officials also told us that the federal rulemaking process for
manufactured housing was slow because manufactured housing was not
a priority for HUD. We found the priority given the program is unclear.
HUD’s strategic plan does not include the manufactured housing program
among those contributing to HUD’s priority goal of promoting healthy,
energy-efficient, and affordable buildings.




Page 14                               GAO-13-52 Manufactured Housing Standards
                             HUD does not maintain data on the number of manufactured houses built
Millions of                  or the distances between vents and air intakes of homes designed with
Manufactured Homes           an outdoor air intake connected to the air distribution system. American
                             Housing Survey estimates showed that in 2009 many of the
Have Been Built              approximately 6.8 million occupied manufactured homes had been built
under the HUD Code           under the HUD Code. Specifically, about 5.5 million of these units had
                             been built after 1975. 10 The 3-foot separation requirement between air
but HUD Has Not              intakes and exhaust vents has been in effect since 1976 and thus applied
Tested the                   to these homes. According to the American Housing Survey, about half
Performance of               (52 percent) of occupied manufactured homes used electricity as their
                             main heating source, and most of the remaining 48 percent used a
Installed Ventilation        combustible fuel source. 11 As we have mentioned, experts said carbon
Systems                      monoxide exposure—although rare—is most likely in homes that use a
                             combustible fuel source, or nearly half of the manufactured homes
                             identified in the survey.

                             According to HUD officials, although it does not have data on the actual
                             distances between vents and air intakes of constructed homes, HUD
                             retains copies of all DAPIA approved design packages, which include
                             requirements for this separation. As validated by DAPIAs, designs of
                             manufactured homes are developed with the intent of meeting the HUD
                             Code. Two large manufacturers we spoke to, which accounted for about
                             60 percent of the market, stated that they did not track the distances
                             between vents and air intakes of each home, but that their homes met
                             HUD standards—that is, the distances were at least 3 feet for homes with
                             air intakes.


Data on the As-Installed     Furthermore, we found that the HUD Code does not require testing of the
Performance of Ventilation   performance of the ventilation system, including the resulting whole-
Systems in Manufactured      house airflow rate of homes, either at the plants or once the homes are
                             put in place. HUD officials told us that the DAPIAs review designs to help
Homes are Limited            ensure the performance of ventilation systems meets the HUD Code. In
                             particular, DAPIAs ensure that designs include the required exhaust fans
                             to move a certain volume of air that should achieve the specified whole-




                             10
                              The relative margins of error for these estimates are between 4.41 and 13.70 percent.
                             11
                               Estimates are from the Census Bureau’s 2009 American Housing Survey. The margins
                             of error are between 1.40 and 4.70 percent.




                             Page 15                                      GAO-13-52 Manufactured Housing Standards
house airflow rate. 12 HUD officials stated that IPIAs are not required to
test the whole-house airflow rate either in the plant or in the field because
the HUD Code does not require it. In contrast, the HUD Code does
require the inspection and testing of other specified features, such as gas
lines, smoke alarms installed at the factory, and plumbing systems. 13

Air quality experts we spoke with emphasized that a variety of factors
could impact the whole-house airflow rate. For example, one expert said
duct leakage and friction could result in airflow losses. Therefore, an
approved design may assume a certain airflow rate for an exhaust fan,
but the quality of construction could reduce the whole-house airflow rate
upon installation. Additionally, several studies by the Department of
Commerce’s National Institute of Standards and Technology (NIST)
indicated that the whole-house airflow rate of manufactured homes
depended on how often the fans were operated, as well as weather and
climate factors. In 2008 and 2010 NIST reported that some airflow rates
in a test home were below levels specified in the HUD Code. Because
HUD does not require testing to validate the performance of ventilation
systems, specifically the resulting whole-house airflow rates, it does not
know how the systems are performing or whether they meet HUD
specifications.

Cooperative research in 2003 involving HUD and the Manufactured
Housing Research Alliance concluded that it was unclear how well whole-
house ventilation systems in manufactured homes performed with respect
to the HUD Code’s whole-house airflow rate performance specification. 14
According to the study and HUD officials, identifying a typical airflow rate
for manufactured homes is challenging because factors such as
temperature, wind, location of the home, and construction type have
varying impacts on the natural infiltration in similar homes. The study
recommended that HUD:



12
  24 C.F.R. § 3280.103 (b). The HUD Code also requires mechanical ventilation systems
to have a manual control and for the instructions to encourage consumers to operate the
system whenever the home is occupied. 24 C.F.R. § 103(b)(4), (6).
13
 24 C.F.R. § 3280.706(l)(8), 3280.208(f), 3280.612.
14
  The Manufactured Housing Research Alliance is now named the Systems Building
Research Alliance. The mission of this nonprofit organization is to develop new
technologies to enhance the value, quality, and performance of both manufactured and
modular homes.




Page 16                                      GAO-13-52 Manufactured Housing Standards
                         •   conduct further research to develop a testing method to determine
                             whether specifications for ventilation design and performance were
                             being met, and
                         •   publish guidelines for achieving the required airflow rate in
                             manufactured homes in a best practices manual to be created for the
                             industry.
                         As of August 2012, MHCC was considering a proposal to adopt an
                         industry standard for residential ventilation that includes testing to ensure
                         that ventilation systems meet performance specifications. Requirements
                         for testing the ventilation system after installation were incorporated in
                         ASHRAE’s ventilation standards for residential homes in 2003. The
                         current proposal with the MHCC includes testing the delivered airflow of
                         the system, using an airflow measuring device to confirm the airflow of
                         the system.

                         HUD officials acknowledged that the recommendations from the 2003
                         study had not been implemented and cited funding issues as reasons for
                         not implementing them. According to HUD officials, HUD has not received
                         negative reports on indoor air quality in manufactured homes that
                         occurred as a direct result of the whole-house ventilation systems.
                         However, without testing of the actual whole-house airflow rates of
                         recently manufactured homes, HUD cannot know whether these homes,
                         as built, meet HUD’s requirement of 0.035 cubic feet per minute for each
                         square foot of interior floor space. Still, the ventilation standards establish
                         standards for airflow, not air quality, although the required airflows are
                         intended to enhance air quality in the home.

                         Measuring the actual airflow achieved by installed ventilation systems
                         would not only permit HUD to know whether its standards are being met,
                         but also permit HUD to better understand the potential impact ventilation
                         systems may have on indoor air quality. In the next section we discuss
                         limitations in HUD’s standard.


The HUD Code Airflow     We found that the performance specifications for the whole-house airflow
Rate Is Based on         rate in the HUD Code were based on industry standards and assumptions
Standards and Research   from nearly 20 years ago. As we stated earlier, HUD has not tested these
                         performance specifications as manufactured homes are built and
from 1993                installed. In 1993, HUD first set a standard for the whole-house airflow




                         Page 17                                  GAO-13-52 Manufactured Housing Standards
              rate, basing it on the ASHRAE standards from 1989 and ventilation
              research by NIST and the U.S. Department of Agriculture’s Forest
              Products Laboratory. 15 The original whole-house airflow rate requirement
              aimed at replacing about one-third of the air in a manufactured home with
              fresh air each hour (that is, 0.35 total air changes per hour). As part of
              this requirement, HUD also assumed natural infiltration would account for
              0.25 air changes per hour and required mechanical ventilation to provide
              the remaining 0.1 air changes per hour. Therefore, the HUD Code in 1993
              specified that each manufactured home shall be provided with
              mechanical whole-house ventilation having a minimum capacity of 0.035
              cubic feet per minute for each square foot of interior space in order to
              achieve a minimum rate of 0.1 air changes per hour. In 2005, HUD
              removed the natural infiltration assumption but kept the same rate for
              mechanical ventilation.

              Since 1993, HUD has continued to specify a mechanical whole-house
              ventilation airflow rate of least 0.035 cubic feet per minute for each
              square foot of interior floor space or its hourly average equivalent. 16 Air
              quality experts emphasized that homes have continued to be built with
              less leakage and greater energy efficiency. Thus, a home built in 1993
              and a home built in 2012 may both meet the HUD whole-house airflow
              rate standard (that relates only to ventilation achieved through
              mechanical means) but may not achieve the same level of air quality.
              Nonetheless, HUD has not reconsidered the appropriateness of its
              standard in achieving an acceptable level of air quality, nor specified an
              acceptable level of air quality. Without further research and testing of its
              whole-house airflow rate standard, HUD may not know the effect of new
              design and construction practices on the overall ventilation performance
              and air quality of manufactured homes.


              Current standards used for site-built and modular homes offer a greater
Conclusions   margin of safety against carbon monoxide exposure than the HUD Code
              standards used for manufactured homes. While carbon monoxide



              15
                As of 2010, ASHRAE requires specific fan flow rates depending on the floor area, the
              number of bedrooms, and the number of occupants rather than the fixed airflow rate of
              0.35 air changes per hour.
              16
                24 C.F.R. § 3280.103(b). In 2005 the HUD Code also first required exhaust fans to
              produce between 50 and 90 cubic feet per minute to achieve this airflow rate.




              Page 18                                       GAO-13-52 Manufactured Housing Standards
exposure resulting from exhaust reentering the home through an air
intake is unlikely, air quality experts we spoke to maintain that industry
standards already required for site-built homes offered a greater margin
of safety to prevent carbon monoxide from reentering a home than the
HUD Code does for manufactured homes. Our analysis also confirmed
that increasing the separation distance between air intakes and exhaust
vents to industry standards decreased the likelihood of carbon monoxide
reentering the home. Further, industry standards for site-built homes call
for the use of a carbon monoxide detector whereas the HUD Code does
not. In response, the MHCC has forwarded safety-designated
recommendations to HUD to update the HUD Code to address concerns
over the separation distance between air intakes and exhaust vents and
the lack of a requirement for carbon monoxide detectors in manufactured
homes.

The differences between the HUD Code and industry standards related to
home ventilation and indoor air quality are due to the regulatory
procedures and time it takes HUD to consider and implement proposed
updates. Although we observed proposals aimed at maintaining similar
standards for manufactured and site-built homes, proposed updates for
manufactured homes lagged behind those made by industry for site-built
and modular homes. HUD’s process for adopting changes to the HUD
Code involving considerable time for proposals to be considered by the
MHCC and HUD has resulted in a lack of action even on safety-related
proposals that the MHCC has put forth, including increasing the
separation requirement for air intakes and exhaust vents and requiring
carbon monoxide detectors. Although MHCC has submitted several
recommendations to HUD, HUD has not implemented any changes to the
HUD Code since 2005, so actual implementation of recent updates may
be years away. We will explore rulemaking and other issues with the
Manufactured Housing Program in further work.

HUD does not maintain data on the actual separation distances between
the fresh air intakes and exhaust vents, but does retain copies of designs
with DAPIA approval, indicating they comply with the HUD Code. We
noted that 5.5 million occupied manufactured homes were built since the
HUD Code took effect with a 3-foot separation requirement, and almost
half of manufactured homes built use combustible furnace fuels.
However, we found limited data available related to the installed
performance of the ventilation systems of manufactured homes
constructed and placed. HUD does not require manufacturers to test the
performance of the ventilation systems installed in manufactured homes
to determine whether the systems actually meet their performance


Page 19                               GAO-13-52 Manufactured Housing Standards
                      specifications. Further, while the HUD Code specifies certain inspections
                      and tests to validate many other features of manufactured homes, HUD
                      does not require manufacturers to conduct performance testing of the
                      ventilation system, specifically the required whole-house ventilation
                      airflow rate. Other research efforts have previously voiced similar
                      concerns over uncertainties as to whether the performance specifications
                      of the ventilation system were being met in manufactured homes.
                      Ultimately, without testing the whole-house airflow rate for constructed
                      manufactured homes, either in the factory or the field, HUD and others
                      cannot be assured as to whether the airflow is ventilating the home as
                      specified.

                      We also found that the current HUD code performance specification for
                      the whole-house ventilation airflow rate is based on standards and
                      research from nearly 20 years ago. Since then, air quality experts and
                      research suggest that the industry has improved the construction of
                      manufactured homes. To the extent that manufactured homes continue to
                      be built tighter and more energy efficient, mechanical ventilation of homes
                      becomes more important for ensuring indoor air quality. HUD’s whole-
                      house airflow rate standard for mechanical ventilation of 0.035 cubic feet
                      per minute per square foot of living space has remained unchanged.
                      Without further assessment of the impact that potential changes in natural
                      air infiltration have on whole-house ventilation, HUD cannot be certain of
                      the air quality in manufactured homes.


                      To better ensure that air ventilation systems in manufactured homes
Recommendations for   perform as specified and meet the HUD Code, we recommend that HUD
Executive Action      develop an appropriate method to test and validate the performance of
                      the ventilation system as part of the HUD certification process.

                      To ensure that its specification for airflow continues to be appropriate, we
                      recommend that HUD reassess the assumptions for the whole-house
                      ventilation specification, working with the MHCC, to determine the
                      appropriate rates, taking into consideration current natural air infiltration,
                      to achieve the whole-house ventilation performance, considering the
                      expected impact such ventilation would have on indoor air quality.


                      We provided a draft of this report to HUD for review and comment. HUD’s
Agency Comments       Acting Assistant Secretary for Housing-Federal Housing Commissioner
and Our Evaluation    provided written comments that are discussed below and presented in



                      Page 20                                 GAO-13-52 Manufactured Housing Standards
Appendix II. HUD also provided technical comments that were
incorporated as appropriate.

HUD agreed with both recommendations, noting that it would bring them
before the MHCC for consideration. HUD also said, however, that it would
require additional funding and resources. Specific to our recommendation
that HUD develop an appropriate method to test and validate the
performance of the ventilation system as part of the HUD certification
process, HUD agreed that such testing and validation could improve the
accuracy of system performance. But HUD also questioned the need for
such testing, given that the current systems were designed and approved
by private design professionals. HUD further noted that no documentation
existed showing that ventilation systems in manufactured homes did not
meet current standards. But as our report points out, HUD lacks such
documentation because it does not systematically test the systems. HUD
also stated that it would be impractical to conduct testing at the factory for
multi-section units. However, testing of the whole-house airflow rate could
occur in the field as well as at factories, when practicable.

We also recommended reassessing the assumptions for the existing
whole-house ventilation airflow rate specification. HUD agreed that a
reassessment of the assumptions used to determine the appropriate rate
could have a positive impact on indoor air quality. HUD also said that it
would need to balance changes in these requirements against costs
incurred by manufacturers and consumers. As we noted in the report, the
existing whole-house ventilation airflow rate requirement (0.035 cubic feet
per minute per square foot of living space) is based on assumptions for
natural air infiltration dating back to 1993. HUD noted in its technical
comments that no evidence existed to support the argument that the
ventilation standards for manufactured homes were less effective than
industry standards. Further, HUD said that its standards provide rates of
mechanical ventilation that are comparable to those provided by industry
standards. However, without further assessment of the impact that
potential changes in natural air infiltration have on whole-house
ventilation, HUD cannot be certain of the air quality in manufactured
homes. Reassessing assumptions made nearly 20 years ago would help
determine whether HUD’s required whole-house ventilation airflow rate
continues to ensure that manufactured homes are properly ventilated.




Page 21                                 GAO-13-52 Manufactured Housing Standards
We are sending copies of this report to appropriate congressional
committees and the Secretary of Housing and Urban Development. The
report also is available at no charge on the GAO website at
http://www.gao.gov.

If you or your staff have any questions about this report, please contact
me at (202) 512-8678 or sciremj@gao.gov. Contact points for our Offices
of Congressional Relations and Public Affairs may be found on the last
page of this report. GAO staff who made major contributions to this report
are listed in appendix III.




Mathew J. Scirè
Director,
Financial Markets and Community Investment




Page 22                               GAO-13-52 Manufactured Housing Standards
Appendix I: Comparison of Different Separation
                Appendix I: Comparison of Different
                Separation Distances Between Air Intakes and
                Exhaust Vents and Impacts on Potential

Distances Between Air Intakes and Exhaust Vents
                Carbon Monoxide Exposure




and Impacts on Potential Carbon Monoxide
Exposure
                Reentry of exhaust occurs when exhaust leaving its vent finds its way to
                an air intake and gets pulled back into the home. The common mitigation
                practice is to provide adequate horizontal or vertical separation between
                the exhaust vent and the air intake such that any reentered air is diluted
                to a greater extent by the time it reaches habitable areas of the home.

                In their Handbook of Fundamentals, the American Society of Heating,
                Refrigerating, and Air-Conditioning Engineers (ASHRAE) provides
                methods for modeling the diluting effect of an exhaust stream mixing with
                open air. ASHRAE officials we spoke with told us that these methods can
                be used to assess solutions to various ventilation problems including
                exhaust air reentry scenarios. Therefore, we used these techniques on a
                simple model of a manufactured home to analyze how much carbon
                monoxide in the exhaust stream of the furnace in the home could be
                diluted by the time it reached an air intake of the home. We analyzed
                different scenarios involving various separation distances between the
                exhaust vent and the air intake to see what effect separation distance
                produced on the amount of dilution provided by open air mixing.

                Dilution of contaminants occurs through mixing of the exhaust stream with
                fresh air as the stream leaves its vent, enters open air, is affected by the
                wind, and spreads away from the vent, dispersing contaminants in the
                stream as it progresses. In general, dilution increases with increasing
                wind speed, as might be expected, because a stronger airflow will aid in
                dispersing contaminant particles, and is inversely proportional to both the
                speed with which the exhaust stream is coming out of the vent, as well as
                the size of the vent opening. This makes sense because increasing
                exhaust speed and increasing vent size, naturally, competes against
                dilution by putting more contaminant into the air.

                However, the mixing is not straightforward, as many factors can influence
                how much dilution takes place. For example, the airflow closer to the
                ground can be disrupted by obstacles such as trees and buildings,
                inducing turbulence in the flow. At roof level, vents and even the pitch of
                the roof can further complicate the flow, creating a mix of eddies and
                zones where the air might get recirculated and trapped near the roof, thus
                restricting the dilution effect. This is sometimes the case at lower exhaust
                speeds and lower wind speeds, where the exhaust plume will not have
                the momentum to rise very high or get dispersed very quickly by the wind
                and may get pushed down and remain near roof level and the air intake.

                In implementing their model, ASHRAE assumes the air intake is
                positioned directly downwind of the exhaust vent and then allows for a


                Page 23                                        GAO-13-52 Manufactured Housing Standards
Appendix I: Comparison of Different
Separation Distances Between Air Intakes and
Exhaust Vents and Impacts on Potential
Carbon Monoxide Exposure




variety of parameters to specify the geometries involved; for example the
height of the roof, the horizontal and vertical separation distances
between the exhaust vent and the air intake, and the size of the exhaust
vent opening. In addition, ASHRAE allows for specifying characteristics of
the exhaust stream, such as the speed with which the exhaust is exiting
the vent, and the initial concentration of a contaminant within the stream
at the vent opening. Finally, ASHRAE models the flow of the air through a
number of factors that include the wind speed, the downwind, cross-wind,
and vertical spread of the plume as it progresses downstream, and the
turbulence intensity of the air, which is controlled by a factor that allows
for specifying the roughness of the terrain over which the air will be
flowing.

In our analysis, we used three different scenarios for separation distances
between the air intake and exhaust vent—3 foot horizontal, 10 foot
horizontal, and 3 foot horizontal with a 3 foot vertical separation. Table 1
also shows the specific parameters we used in our analysis. These
included a manufactured home with a roof height of 10 feet and an
exhaust vent diameter of 4 inches. We used an initial carbon monoxide
concentration in the exhaust stream of 200 ppm, which experts have told
us could occur in the exhaust stream of a malfunctioning furnace.




Page 24                                        GAO-13-52 Manufactured Housing Standards
                                           Appendix I: Comparison of Different
                                           Separation Distances Between Air Intakes and
                                           Exhaust Vents and Impacts on Potential
                                           Carbon Monoxide Exposure




Table 1: Parameters Used in Our Analysis

Parameter                               Value                         Notes
Height of the roof                      10 ft                         Height of the roof off the ground at the gutter.
Horizontal distance between the         Variable                      We assessed cases with horizontal separation distances of 3 feet
exhaust vent and the air intake                                       and 10 ft.
Vertical separation distance between    Variable                      We assessed cases of no separation (0) and a separation of 3 feet.
the exhaust vent and the air intake
Diameter of the exhaust vent opening    4 inches                      Diameter of the exhaust vent opening. We considered the exhaust
                                                                      vent to be capped.
Exhaust stream speed                    1000 feet per minute          ASHRAE representatives mentioned 100-2000 fpm are typical
                                        (fpm)                         values for residential furnaces.
Initial carbon monoxide concentration   200 ppm                       Concentration at the exhaust vent opening of an assumed carbon
                                                                      monoxide component in the exhaust stream.
Wind speed                              Variable                      We assessed scenarios varying the wind speed from 1 to 26 mph
                                                                      (about 88 to 2288 fpm).
Roughness factor                        2.132                         Characterizes airflow over the terrain. This is the value ASHRAE
                                                                      specifies for a suburban setting. For comparison purposes, a flat
                                                                      desert would have a value of 0.03 while an urban setting would
                                                                      have a value of 6.0.
                                           Source: GAO analysis based on the ASHRAE Handbook of Fundamentals.



                                           Figure 5 represents the results of our analysis and illustrates contaminant
                                           concentration at the air intake as a function of wind speeds for various
                                           exhaust vent to air intake separations. Here it can be seen that increasing
                                           the horizontal separation to 10 feet or adding a 3 foot vertical separation
                                           to the 3 foot horizontal separation reduces the concentration at the air
                                           intake more than the 3 foot horizontal separation alone does. For
                                           example, in a light 1 mph wind, exhaust with a carbon monoxide
                                           concentration of 200 ppm would be diluted to approximately 50 ppm at an
                                           air intake separated 3 feet horizontally from the exhaust vent. Increasing
                                           the separation between the exhaust vent and air intake to either 10 feet
                                           horizontally or 3 feet horizontally and 3 feet vertically in a 1 mph wind
                                           results in carbon monoxide concentrations of less than 10 ppm at the air
                                           intake.




                                           Page 25                                                      GAO-13-52 Manufactured Housing Standards
                                         Appendix I: Comparison of Different
                                         Separation Distances Between Air Intakes and
                                         Exhaust Vents and Impacts on Potential
                                         Carbon Monoxide Exposure




Figure 5: Contaminant Concentration at Air Intake for Different Wind Speeds and Various Exhaust Vent to Air Intake
Separations




                                         Page 26                                        GAO-13-52 Manufactured Housing Standards
Appendix II: Comments from the Department
             Appendix II: Comments from the Department
             of Housing and Urban Development



of Housing and Urban Development




             Page 27                                     GAO-13-52 Manufactured Housing Standards
Appendix II: Comments from the Department
of Housing and Urban Development




Page 28                                     GAO-13-52 Manufactured Housing Standards
Appendix III: GAO Contact and Staff
                  Appendix III: GAO Contact and Staff
                  Acknowledgements



Acknowledgements

                  Mathew J. Scirè, (202) 512-8678 or sciremj@gao.gov
GAO Contact
                  In addition to the contact named above, Andy Finkel (Assistant Director),
Staff             Mike Armes, James Ashley, Tim Bober, Bill Carrigg, Emily Chalmers,
Acknowledgments   Pamela Davidson, Juliann Gorse, Barry Kirby, John McGrail, Marc
                  Molino, and Nadine Garrick Raidbard, made key contributions to this
                  report.




(250641)
                  Page 29                               GAO-13-52 Manufactured Housing Standards
GAO’s Mission         The Government Accountability Office, the audit, evaluation, and
                      investigative arm of Congress, exists to support Congress in meeting its
                      constitutional responsibilities and to help improve the performance and
                      accountability of the federal government for the American people. GAO
                      examines the use of public funds; evaluates federal programs and
                      policies; and provides analyses, recommendations, and other assistance
                      to help Congress make informed oversight, policy, and funding decisions.
                      GAO’s commitment to good government is reflected in its core values of
                      accountability, integrity, and reliability.

                      The fastest and easiest way to obtain copies of GAO documents at no
Obtaining Copies of   cost is through GAO’s website (http://www.gao.gov). Each weekday
GAO Reports and       afternoon, GAO posts on its website newly released reports, testimony,
                      and correspondence. To have GAO e-mail you a list of newly posted
Testimony             products, go to http://www.gao.gov and select “E-mail Updates.”

Order by Phone        The price of each GAO publication reflects GAO’s actual cost of
                      production and distribution and depends on the number of pages in the
                      publication and whether the publication is printed in color or black and
                      white. Pricing and ordering information is posted on GAO’s website,
                      http://www.gao.gov/ordering.htm.
                      Place orders by calling (202) 512-6000, toll free (866) 801-7077, or
                      TDD (202) 512-2537.
                      Orders may be paid for using American Express, Discover Card,
                      MasterCard, Visa, check, or money order. Call for additional information.
                      Connect with GAO on Facebook, Flickr, Twitter, and YouTube.
Connect with GAO      Subscribe to our RSS Feeds or E-mail Updates. Listen to our Podcasts.
                      Visit GAO on the web at www.gao.gov.
                      Contact:
To Report Fraud,
Waste, and Abuse in   Website: http://www.gao.gov/fraudnet/fraudnet.htm
                      E-mail: fraudnet@gao.gov
Federal Programs      Automated answering system: (800) 424-5454 or (202) 512-7470

                      Katherine Siggerud, Managing Director, siggerudk@gao.gov, (202) 512-
Congressional         4400, U.S. Government Accountability Office, 441 G Street NW, Room
Relations             7125, Washington, DC 20548

                      Chuck Young, Managing Director, youngc1@gao.gov, (202) 512-4800
Public Affairs        U.S. Government Accountability Office, 441 G Street NW, Room 7149
                      Washington, DC 20548




                        Please Print on Recycled Paper.