[Federal Register Volume 82, Number 118 (Wednesday, June 21, 2017)]
[Proposed Rules]
[Pages 28279-28288]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2017-12964]


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DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT

24 CFR Part 3285

[Docket No. FR-6023-N-01]


Interpretative Bulletin for Model Manufactured Home Installation 
Standards Foundation Requirements in Freezing Temperature Areas Under 
24 CFR 3285.312(b)

AGENCY:  Office of the Assistant Secretary for Housing--Federal Housing 
Commissioner, HUD.

ACTION: Notice of proposed installation Interpretative Bulletin I-1-17.

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SUMMARY: The purpose of this proposed Interpretative Bulletin (IB) is 
to provide guidance for designing and installing manufactured home 
foundations in areas subject to freezing temperatures with seasonal 
ground freezing, in accordance with the Model Manufactured Home 
Installation Standards, wherever soil conditions are susceptible to 
frost heave. Specifically, this guidance is being provided for 
designing and installing manufactured home foundation systems in areas 
where frost susceptible seasonally frozen ground conditions are 
encountered and when footings do not extend below the frost depth at 
the site. These types of foundation systems include monolithic slab 
systems, ``frost-protected shallow foundations'' (FPSF)--insulated 
foundations, and alternative foundation systems that include foundation 
variations termed by industry as frost free footing systems or frost 
free foundations (FFF). Guidance is also being provided in this 
interpretative bulletin for installing manufactured home foundations, 
when non-frost susceptible soil conditions are available at the site to 
protect foundations against the effects of frost heave.

DATES: Comment Due Date: August 21, 2017.

ADDRESSES: Interested persons are invited to submit comments regarding 
this Interpretative Bulletin to the Regulations Division, Office of 
General Counsel, Department of Housing and Urban Development, 451 
Seventh Street SW., Washington, DC 20410-0500. Room 10276, Washington, 
DC 20410-0500. Communications must refer to the above docket number and 
title. There are two methods for submitting public comments. All 
submissions must refer to the above docket number and title.
    1. Submission of Comments by Mail. Comments may be submitted by 
mail to the Regulations Division, Office of General Counsel, Department 
of Housing and Urban Development, 451 7th Street SW., Room 10276, 
Washington, DC 20410-0500.
    2. Electronic Submission of Comments. Interested persons may submit 
comments electronically through the Federal eRulemaking Portal at 
www.regulations.gov. HUD strongly encourages commenters to submit 
comments electronically. Electronic submission of comments allows the 
commenter maximum time to prepare and submit a comment, ensures timely 
receipt by HUD, and enables HUD to make them immediately available to 
the public. Comments submitted electronically through the 
www.regulations.gov Web site can be viewed by other commenters and 
interested members of the public. Commenters should follow the 
instructions provided on that site to submit comments electronically.

    Note:  To receive consideration as public comments, comments 
must be submitted through one of the two methods specified above. 
Again, all submissions must refer to the docket number and title of 
the rule.

    No Facsimile Comments. Facsimile (FAX) comments are not acceptable.
    Public Inspection of Public Comments. All properly submitted 
comments and communications submitted to HUD will be available for 
public inspection and copying between 8 a.m. and 5 p.m. weekdays at the 
above address. Due to security measures at the HUD Headquarters 
building, an advance appointment to review the public comments must be 
scheduled by calling the Regulations Division at 202-708-3055 (this is 
not a toll-free number). Individuals with speech or hearing impairments 
may access this number through TTY by calling the Federal Information 
Relay Service at 800-877-8339. Copies of all comments submitted are 
available for inspection and downloading at www.regulations.gov.

FOR FURTHER INFORMATION, CONTACT: Pamela Beck Danner, Administrator, 
Office of Manufactured Housing Programs, Office of Housing, Department 
of Housing and Urban Development, 451 Seventh Street SW., Washington, 
DC 20410; telephone (202) 708-6409 (this is not a toll-free number). 
Persons with hearing or speech impairments may access this number via 
TTY by calling the toll free Federal Relay Service at 1-800-877-8389.

SUPPLEMENTARY INFORMATION:

I. Background

    The National Manufactured Housing Construction and Safety Standards 
Act of 1974 (42 U.S.C. 5401-5426) (the Act) as amended in 2000 
authorizes the Department to establish Model Manufactured Home 
Installation Standards (Installation Standards) and establish an 
installation program to enforce those Installation Standards. The 
Installation Standards are at 24 CFR part 3285, and installation in 
freezing temperature areas is covered at Sec.  3285.312(b). Section 
604(a)(3) of the Act as amended in 2000 also created the Manufactured 
Housing Consensus Committee (MHCC). Section 604(b)(3) of the Act 
directs HUD to provide the MHCC with an opportunity to review any HUD 
proposed Interpretative Bulletin and to provide written comments to the 
Department for a period of up to 120 days.
    Frost-protected shallow foundations have been successfully used 
both domestically and internationally in residential and commercial 
applications for over 50 years as a means to avoid deeper and more 
costly foundation systems. However, as a result of recent problems and 
inquiries related to the proper design, use, and installation of

[[Page 28280]]

manufactured home frost protected foundation systems in areas subject 
to freezing temperature conditions, HUD commissioned a study and report 
to assess both foundation design and installation practices for 
manufactured homes located in temperature areas with seasonally frozen 
ground. HUD provided the MHCC with a report of its findings on October 
26, 2016, entitled ``An Assessment of Design and Installation Practices 
for Manufactured Homes in Climates with Seasonally Frozen Ground'' 
prepared by SEBA Professional Services, LLC (https://portal.hud.gov/hudportal/documents/huddoc?id=10-07-16-Frost-free-Found.pdf), and 
announced it would form the basis for an Interpretative Bulletin to be 
issued on the subject.
    The study and resulting report found some key factors needed for 
long-term and consistent success require special considerations that 
are often neglected, particularly for FFF designs and installations 
that rely on well-drained and non-frost susceptible soil conditions. 
These factors include appropriately engineered installation details, 
site investigation practices, fulfillment of responsibilities by all 
parties associated with manufactured home installation, and 
verification procedures to ensure that important design conditions are 
actually being achieved in practice. Accordingly, this Interpretative 
Bulletin was developed for the purpose of clarifying requirements and 
providing practical guidance for the manufactured housing industry when 
designing or setting foundations for manufactured homes in locations 
subject to freezing temperatures with seasonal ground freezing.
    HUD also indicated at the October 26th meeting of the MHCC, that it 
would consider any comments received from the MHCC on the report and 
scheduled a teleconference on November 28, 2016, with the Regulatory 
Subcommittee of the MHCC and with the MHCC on December 12, 2016, to 
receive feedback and recommendations from the subcommittee and MHCC. As 
a result of those discussions, the Regulatory Subcommittee recommended 
that HUD draft an Interpretative Bulletin for the December 12, 2016, 
teleconference with the full MHCC, taking into consideration the 
comments from the Regulatory Subcommittee teleconference and subsequent 
comments from the MHCC. A large part of the discussion focused on what 
constitutes acceptable engineering practice. Some members of the 
subcommittee expressed concerns on whether the SEI/ASCE 32-01 (ASCE 32) 
Standard should exclusively define accepted engineering practice or if 
other engineering alternatives should be allowed. During the December 
12, 2016, conference call with the MHCC, the committee developed and 
approved the following recommendations and comments to its draft 
Interpretative Bulletin. These comments were also approved by a 
subsequent letter ballot. The ballot results were provided to HUD by 
the MHCC's Administering Organization (AO) on January 23, 2017. HUD's 
response to each of the points raised by the MHCC is as follows:
    1. Tone of the IB needs to be more positive.
    HUD Response: A statement has been added above to indicate that 
frost protected shallow foundations have been successfully used both 
domestically and abroad for than 50 years.
    2. The focus of the IB should be to inform and educate.
    HUD Response. HUD believes that the IB focus is both informative 
and provides education to all respective participants in the 
installation process.
    3. The IB should focus on compliance with 3285.
    HUD Response: The guidance in the IB does focus on both foundation 
design guidelines and compliance with the provisions for foundations in 
freezing temperature areas in 3285.312(b) of the Model Installation 
Standards.
    4. The IB should be simplified (too lengthy).
    HUD Response: HUD does not agree as the guidance cannot be further 
simplified in this proposed IB, since it is both practical and 
technical and, in general, provides a recipe for compliance with the 
Model Installation Standards.
    5. FFF definition and FPSF definition.
    HUD Response: A definition has been added for a Frost Protected 
Shallow Foundation (FPSF). However, as there is no generally recognized 
definition of a frost free foundation (FFF), HUD is requesting comments 
from the public on a suitable technical definition and has reserved a 
space in the IB for a definition of the term.
    6. Clarify site specific foundation.
    HUD Response: A site specific foundation means a foundation system 
that has been designed for a specific site.
    7. Target audience should be installers, local jurisdiction, 
regulators, and manufacturers.
    HUD Response: HUD agrees and focused the four options in the IB on 
those entities and organizations.
    8. The problem doesn't seem to appear in all states and how to 
solve that problem.
    HUD Response: Comments are being requested on other verifiable 
strategies that may not be addressed in this IB that have been 
effective and successfully used in other states.
    9. Ensure additional cost are not incurred due to IB.
    HUD Response: This IB has been developed to clarify the intent of 
the standards with technical concepts that will avoid costly foundation 
and structural repairs due to frost heave.
    10. Reference to actual designs and specific engineering language 
in the IB should be removed.
    HUD Response: Reference to actual designs has been removed from the 
IB. However, it remains necessary to utilize some engineering 
terminology to explain certain aspects of the foundation options 
contained in this IB.
    11. Ensure IB doesn't exceed reasonable accepted engineering 
practice as required in Sec.  3285.312(b)(2).
    HUD Response: HUD believes that all aspects and options contained 
in this IB conform to acceptable engineering practice.
    12. Remove reference to the SEBA report from the IB.
    HUD Response: HUD agrees and has taken out the SEBA report.
    13. Remove Local Authority Having Jurisdiction (LAHJ) where the 
plan approval is not required and in HUD administered states (Sec.  
3286.3, HUD administered installation program) from the IB.
    HUD Response: HUD does not agree with this recommendation as an 
LAHJ can both require plan approval and establish provisions which 
exceed the requirements of HUD's Model Installation Standards in states 
where HUD administers the installation program.
    The MHCC also provided HUD with the specific suggested text 
revisions to the Interpretative Bulletin. The MHCC suggested revisions 
are available at https://www.xxxxxxxxx (Appendix E). However, HUD did 
not agree with or accept the MHCC recommendation to delete the 
statement regarding the SEI/ASCE 32-01 Standard generally providing the 
bases for acceptable engineering practice (see page 10 of Appendix E); 
HUD consolidated MHCC recommendations for manufacturers on Recommended 
Practices and Procedures (see page 11 of Appendix E); HUD deleted the 
Recommendations for Retailers and Installers as recommended by the MHCC 
(see page 12 of Appendix E); HUD did not accept the MHCC recommendation 
regarding deleting

[[Page 28281]]

statements regarding the assignment of design responsibilities to local 
authorities (see page 13 of Appendix E); HUD also did not accept the 
MHCC recommendation to delete the statement regarding submitting the 
foundation plan to the local authority having jurisdiction if 
applicable but did delete the statement regarding the sealing of 
foundation plans by an engineer or architect that is licensed in the 
state where the installation is occurring (see page 13 of Appendix E); 
HUD modified the language for regulatory officials and inspectors based 
in part on recommendations of the MHCC (see page 14 of Appendix E); HUD 
accepted the editorial revisions recommended by the MHCC for Option 1 
(see page 15 of Appendix E); and HUD also accepted the MHCC 
recommendation to delete the requirements for vents in skirting to be 
automatically closing (see page 16 of Appendix E).
    HUD has considered the above recommendations and comments from the 
MHCC and included them where it deemed appropriate in the text of the 
Interpretative Bulletin.

II. The Interpretative Bulletin

    This guidance is being issued in response to numerous requests, 
inquiries, and questions regarding how to comply with HUD's 
requirements for foundations in freezing temperature areas, in 
accordance with 24 CFR 3285.312(b) of the Model Manufactured Home 
Installation Standards, when footings do not extend below the frost 
depth at the site. Engineered foundations designs such as monolithic 
slab systems (Sec.  3282.312(b)(2)) placed on a layer of well drained 
undisturbed ground or fill material that is not susceptible to frost 
and frost protected shallow foundations (FPSF), which are insulated 
foundations (Sec.  3282.312(b)(3)) that rely on insulation to prevent 
ground freezing as well as other alternative foundation systems 
including industry termed ``frost free foundations'' have great appeal 
and potential in freezing temperature areas as a cost-effective means 
of installing manufactured homes on seasonally-frozen ground. 
Understandably, their use has been promoted and increased in recent 
years as a means for reducing manufactured housing installation costs 
when compared to using conventional or proprietary foundation support 
systems in freezing temperature areas. However, some key factors 
important to their long-term and consistent success require special 
considerations that are often neglected, particularly for FFF designs 
and installations. These factors include appropriately engineered 
installation details, site investigation practices, and verification 
procedures to ensure that important design conditions are actually 
being achieved in practice.
    Important factors or design considerations in any frost-protected 
foundation include:
     Clarity of technical requirements;
     definite criteria for determining soil frost 
susceptibility and soil moisture sub-surface drainage conditions; and
     guidance on water table depth to determine if the site is 
suitably well drained.
    In addition, for foundations being placed on non-frost susceptible 
soil, it is also necessary to provide guidance on appropriate site-
specific details such as the depth of non-frost-susceptible soil or 
fill layers required for the frost depth encountered at the site and 
the layout of sub-surface drainage, when sub-surface site conditions 
are not well drained. Clarification and accuracy of roles during the 
site testing and installation process also play an important part in 
ensuring that frost-protected foundation designs meet the requirements 
of HUD's Manufactured Home Model Installation Standards in 24 CFR 
3285.312.
    The HUD commissioned study reviewed a selection of representative 
alternative foundation plans including FFF designs in current use for 
consistency with the HUD code, the ASCE 32 standard titled Design and 
Construction of Frost Protected Shallow Foundations, and generally 
accepted engineering practice. These reviews and additional technical 
information (including terminology and technical references) are 
included in an engineering assessment report at the URL provided in 
this notice. Thus, the report provides both a reference and technical 
basis for the guidance and recommendations included herein.
    A summary of key findings from the engineering assessment are as 
follows:
     One of the reviewed FFF designs demonstrated an 
appropriate application of the HUD code and ASCE 32 standard's 
technical requirements for frost protection of foundations. Thus, it is 
possible to develop a compliant FFF design in accordance with 
acceptable engineering practice or ASCE 32.
     All other reviewed FFF designs contained a number of flaws 
or non-conformances, including:
    [cir] A lack of clarity of technical requirements in manufacturer 
installation instructions, details, and notes;
    [cir] Missing or vague criteria for identification and measurement 
of soil frost susceptibility;
    [cir] Missing or vague guidance for determining soil moisture, sub-
surface drainage conditions, and water table depth in relation to 
determining if the site is ``well drained'' and suitable for an FFF 
installation; and
    [cir] Missing guidance to direct appropriate site specific 
adjustments of important installation details (e.g., depth of non-
frost-susceptible soil or fill layers and lay-out of sub-surface 
drainage when required).
     A number of the FFF installation designs reviewed showed a 
pattern of confused roles and responsibilities, often assigning design 
decisions and site engineering evaluations to local regulatory 
officials who are typically neither qualified nor trained in foundation 
engineering or soil mechanics and engineering. Furthermore, they are 
not charged with such responsibilities because it may pose a conflict 
of interest (i.e., enforcers making design and construction decisions 
or judgments on matters they will be enforcing) and a potential 
conflict with state engineering practice laws (i.e., conducting 
engineering or design activities for which they are not licensed). 
Consequently, this practice can lead to an incorrect selection of the 
proper foundation and drainage system for the site.
    Consequently, most of the reviewed alternative foundation designs 
including FFF designs were found to be not in conformance with the HUD 
Code and the ASCE 32 reference standard for frost-protection of shallow 
foundations. In addition, one state's installation rules were reviewed 
and provisions related to FFF design and installations were found to be 
similarly non-compliant. Thus, a need exists to clarify requirements 
and provide guidance for proper and compliant applications of FFF 
designs as an alternative to a conventional (frost depth) footing or a 
conventional FPSF design using insulation to protect against ground 
freezing in accordance with acceptable engineering practice or the ASCE 
32 standard.
    In view of the above, each organization involved in the process of 
foundation design, approval, and installation has responsibilities that 
need to be met. Key areas and responsibilities for each organization or 
entity are as follows:
     Manufacturers need to ensure their foundation designs 
fully comply with 24 CFR 3285, Model Manufactured Home Installation 
Standards (HUD Code) by use of acceptable engineering practice or 
applicable provisions of the SEI/ASCE 32-01 Standard, Design and 
Construction of Frost-Protected Shallow Foundations (ASCE 32). In 
general, the basis and design principles for acceptable engineering 
practice should

[[Page 28282]]

be consistent with the provisions of the ASCE 32 Standard. However, 
this interpretative bulletin is not intended to preclude the use of 
other alternatives such as engineered foundation designs provided they 
result in comparable protection against frost heave that would be 
provided by the ASCE 32 Standard.
     Manufacturers should review and, as appropriate, delete or 
revise any installation instructions that rely exclusively on surface 
drainage to prevent the effects of frost heave, as such installations 
do not comply with acceptable engineering practices or ASCE 32.
     Manufacturers should inform installers in their 
installation instructions and on all approved foundation plans that 
prior to beginning the installation, a site-specific soil test or other 
evidence is required to determine soil frost susceptibility, the water 
table level, and sub-surface drainage conditions.
     Retailers should verify that the installations are 
performed only by licensed installers.
     Design professionals and Design Approval Primary 
Inspection Agencies (DAPIAs) need to ensure that foundation designs 
comply with all aspects of the HUD Code as provided in 24 CFR 3285.312. 
Designs that rely on surface drainage exclusively or do not specify the 
means of assessing frost susceptibility of soils and their sub-surface 
drainage characteristics should be disapproved or revised to meet the 
provisions of this Interpretative Bulletin. Frost protected foundation 
designs that were approved prior to the effective date of October 28, 
2008, of HUD's Installation Program, should be reviewed and re-approved 
for compliance with 24 CFR 3285. Additionally, design and installation 
responsibilities may not be delegated to local regulatory authorities.
     Installers should consider all sites in freezing 
temperature areas as frost susceptible unless a soil test or other 
evidence is provided to prove the site is non-frost susceptible.
     To ensure compliance with acceptable engineering practices 
or ASCE 32, installers should never install a new home on a site that 
has conditions not covered in the manufacturer's installation 
instructions or the DAPIA approved engineered foundation plan, and 
should bring the specific site conditions to the professional engineer 
or registered architect of record for assessment or obtain the services 
of another professional engineer or registered architect to assess the 
site conditions and adequacy of the foundation design for the site. 
Once the plan is updated to address site conditions and sealed, it 
should be sent to the manufacturer and its DAPIA for approval. The plan 
should then be submitted to the LAHJ, as applicable. Installers should 
not use any design that assigns responsibility to them for assessing 
frost susceptibility and sub-surface drainage conditions without proper 
soil analysis.
     Regulatory officials and inspectors should reject 
installation plans that require them to take on any aspect of design 
responsibility. If a site is claimed to have soil that is non-frost 
susceptible and that is well-drained, soil tests or other evidence must 
be provided to the regulatory official and/or inspector.
     Manufacturer's installation instructions including DAPIA 
approved engineered foundation plans should be available on-site during 
inspections. If these plans are not available, the home cannot pass 
inspection.
     In areas where no set local frost depth is determined, the 
depths corresponding with the Air Freezing Index (Figure 1) may be 
used.
     Installation rules in both states and local municipalities 
should be compared to the ASCE 32 standard and the HUD Code to ensure 
conformity.
    In view of the above described concerns, this Interpretative 
Bulletin was developed for the purpose of clarifying requirements and 
providing practical guidance for the manufactured housing industry when 
designing or setting foundations for a manufactured home in locations 
subject to freezing temperatures with seasonal ground freezing. This 
guidance is intended for first-time installations, not replacement 
installs when current foundations exist on site.
    In summary, in order to resolve the identified problems and 
previously discussed concerns in this Preamble associated with certain 
foundation designs and installation practices in temperature areas 
subject to freezing, all responsible parties in the process should 
follow the guidance in this Interpretative Bulletin. These concerns and 
issues involve designers, DAPIAs, manufacturers, installers, and 
regulatory authorities. The most important factor in reducing problems 
are properly designed installation instructions giving appropriate 
direction and details for installers to implement and regulatory 
officials to verify and inspect. Because this over-arching concern is 
applicable to all methods of installation related to foundation frost-
protection, specific recommendations and guidance for various design 
and installation options are provided in the Interpretative Bulletin.
    Request for Comments: HUD is soliciting comments from the public on 
the following:
    1. How should the term frost free foundation be defined for use and 
context with this Interpretative Bulletin?
    2. Are there any other alternative engineered foundation designs, 
including floating engineered slab designs and pile foundation systems, 
etc. that should be included for use with this Interpretative Bulletin? 
If so, under what conditions and criteria should these systems be 
permitted?
    3. Please provide information on other strategies, that are 
currently not included in this proposed Interpretative Bulletin, that 
have been successfully used or employed to resist the effects of frost 
heave.

Installation Interpretative Bulletin I-1-17

Foundation Requirements in Freezing Temperature Areas

    This Interpretative Bulletin is being issued to provide guidance 
for all parties associated with designing and installing manufactured 
home foundation systems in areas subject to freezing temperatures in 
accordance with 24 CFR 3285.312(b) of HUD's Model Manufactured Home 
Installation Standards.

Definitions

    Frost Free Foundation (FFF) [Reserved].
    Frost Protected Shallow Foundation (FPSF) means a foundation 
protected from frost heave by insulating the foundation in accordance 
with acceptable engineering practice or with the provisions in SEI/ASCE 
32-01, Design and Construction of Frost Protected Foundations (ASCE 32) 
to retard frost penetration below the foundation in order to allow 
shallower footing depths to be used. Use of well drained non-frost 
susceptible soils is also included as FPSFs for certain applications 
(i.e., monolithic slab systems, alternative foundations).

I. Recommended Practices and Procedures

    The following recommendations, practices and procedures should be 
followed by all parties involved in manufactured home installations in 
order to ensure that foundations installed in freezing temperature 
areas are not subject to frost heave and comply with the provisions of 
HUD's Model Manufactured Home Installation Standards.

[[Page 28283]]

1. Recommendations for Manufacturers
    Manufacturers should require that design professionals who submit 
plans to them for approval, as required by 24 CFR 3285.2(c)(1)(ii), 
develop foundation frost-protection installation methods that comply 
with applicable provisions of the HUD's Model Manufactured Home 
Installation Standards, 24 CFR 3285.312(b)(2) or (3). To ensure 
consistent and effective conformance, options with detailed guidance 
for complying designs are provided below and should be followed. These 
directions should also be incorporated into their Manufacturer's 
Installation Instruction manual as required by 24 CFR 3285.2(c)(2).
     Current Frost Free Foundation (FFF) installation 
instructions that rely exclusively on surface drainage as a means of 
foundation frost-protection should either be removed from the 
manufacturer's installation instructions or immediately revised.
     Manufacturer's installation instructions for monolithic 
slab and alternative foundation designs including FFF designs should 
indicate that, prior to commencement of installation, the steps to be 
taken to verify through soil tests or existing site soil records that 
the site soil is non-frost-susceptible and that a ground water 
assessment should be done to verify that the soil is ``well-drained'' 
with a water table depth consistently and sufficiently below the frost 
line.
     To facilitate installations in locations subject to 
freezing, manufacturer instructions should have at least one example of 
an acceptable foundation system for frost susceptible and non-frost 
susceptible soil conditions for use in freezing temperature areas. 
These designs are to have a design professional's seal, and if not 
previously part of the manufacturer's installation instructions, be 
approved by the manufacturer and its Design Approval Primary Inspection 
Agency (DAPIA).
2. Recommendations for Design Professionals and DAPIAs
    Foundation frost-protection methods used for installation designs 
need to comply with HUD's Model Manufactured Home Installation 
Standards by use of acceptable engineering practice or the ASCE 32 
standard. To ensure consistent and effective conformance, alternatives 
with detailed guidance for development of complying designs by 
manufacturers and for DAPIA review and approval are provided in the 
next section of this Interpretative Bulletin, ``Design Options, 
Compliance Checklists, and Installation Practices''.
     Alternative foundation designs including FFF designs that 
rely exclusively on surface drainage as a means of foundation frost-
protection should be removed from manufacturer's installation 
instructions and its DAPIA approval withdrawn or be immediately 
revised.
     Alternative foundation designs that do not specify 
appropriate means of assessing the frost-susceptibility of soils and 
their sub-surface drainage characteristics on a site-specific basis 
should either be removed from use and the manufacturer's installation 
instructions and DAPIA approval withdrawn or immediately revised.
     Alternative foundation designs including FFF designs that 
assign design responsibilities to local regulatory authorities, such as 
assessing site drainage, water table depth, or soil frost-
susceptibility should be removed from use and the manufacturer's 
installation instructions and DAPIA approval withdrawn or immediately 
revised.
3. Recommendations for Installers
    When installing a new home on a site that has conditions not 
covered in the manufacturer's installation manual or in a DAPIA 
approved alternative engineered foundation plan, the special site 
conditions should be brought to the attention of the engineer or 
architect of record. If there is no engineer or architect of record, a 
licensed engineer or licensed architect should be retained to evaluate 
the conditions and then design a plan to install the home. Once this 
plan is finalized and sealed, it must be sent to the manufacturer and 
its DAPIA for approval per 24 CFR 3285.2(c)(1)(ii). The plan should 
also be submitted to the LAHJ for approval if applicable.
     Installers should never install manufactured homes using 
alternative foundations or FFF installation designs that rely 
exclusively on surface drainage as a means of frost protection.
     Installers should never initiate an FFF installation where 
the instructions require them to take on design responsibility of 
assessing soil frost-susceptibility and sub-surface drainage conditions 
without proper soil testing and analysis. Instead, installers should 
verify that appropriate soil testing and site assessment for use of any 
given foundation design has been completed prior to initiating an 
installation.
     Prior to installation of an alternative foundation 
including an engineered system that is not included in the 
manufacturer's installation instructions, installers need to verify 
that the installation plan is stamped by an engineer or architect of 
record as well as approved by the manufacturer and its DAPIA.
     Installers should only use foundation plans that have been 
approved by the manufacturer and its DAPIA on or after January 1, 2009, 
the effective date of HUD's installation program.
4. Recommendations for Local Regulatory Officials and Inspectors
    Regulatory officials and inspectors should verify compliance with 
manufacturer DAPIA approved installation designs including provisions 
for subsurface drainage, water table depth, requirements for non-frost-
susceptibility of soils, etc., when required by the design for a given 
site.
     Where a site is claimed to have non-frost-susceptible and 
``well-drained'' soils as a basis for setting foundation pads or 
footings above the design frost depth, evidence should be required 
including soils tests or pre-existing site-specific soil records and 
site sub-surface drainage and groundwater investigation by a qualified 
soils laboratory or soils engineering professional or geologist. Single 
site soil samples may be taken by the installer or by qualified soil 
engineering professionals with the soil tests done by a qualified soils 
engineering laboratory or soils engineering professional. The standard 
for non-frost susceptible soil is that no more than 6% by mass can pass 
through a #200 sieve in accordance with ASTM D422-63(2007)e2, Standard 
Test Method for Particle-Size Analysis of Soils (ASTM D422).
     Regulatory officials should assure that any DAPIA approved 
alternate foundation plans and the manufacturer installation 
instructions are on site and available during inspections. If approved 
installation plans are not available on site during inspections, the 
home cannot pass inspection.
    In areas where the local frost depth is unavailable, or not 
documented, local regulatory officials should consider permitting 
design frost depths to be determined in accordance with Table 1. Design 
Frost Depth for Footings and Figure 1. U.S. Air Freezing Map Index.

II. Design Options, Checklists and Installation Best Practices

Option #1: Checklist for Conventional Footings in Freezing Temperature 
Areas

HUD Code, 24 CFR 3285.312(b)(1)
     Obtain the local-design frost depth for footings from 
either of the following:

[[Page 28284]]

    [cir] The local authority having jurisdiction (LAHJ),
    [cir] Use Table 1 with the site's Air-Freezing Index (AFI) from 
Figure 1,\1\ or
---------------------------------------------------------------------------

    \1\ A list of AFI values for various states and counties can be 
found in the 2015 International Residential Code (IRC), Table 
R403.3(2), published by the International Code Council, Inc., and 
used as the model building code for most states.
---------------------------------------------------------------------------

    [cir] Consult with a registered professional engineer, registered 
architect, or registered geologist.
     When using Table 1 and Figure 1 to determine frost depth 
for footings, the depth of interior pier footings complying with 
footnote (b) of Table 1 may be taken as one-half the depth required in 
Table 1.
     Based on the required frost depth for footings, dig the 
footing to the frost depth.
     Check the soil bearing at depth of the footing with a 
torque probe, pocket penetrometer or other suitable testing device.
     Based on the tested soil bearing value, properly size the 
footing according to the manufacturer's installation instructions or 
use the Table in 24 CFR 3285.202 in the HUD Code.
     Place footing pads and construct piers or supports at 
locations specified in accordance with the manufacturer's installation 
instructions.
     Backfill as needed and grade the site as required for 
drainage in accordance with 24 CFR 3285.203:
    [cir] Crown the finish grade at the centerline of the foundation
    [cir] Slope grade a minimum of \1/2\-inch per foot for a minimum 
distance of 10 feet away from the home perimeter.

              Table 1--Design Frost Depth for Footings \a\
------------------------------------------------------------------------
                                                           Minimum depth
            Air-freezing index [see Figure 4]              \b\ (inches)
------------------------------------------------------------------------
<=50....................................................               3
250.....................................................               9
350.....................................................              12
500.....................................................              16
1,000...................................................              24
1,500...................................................              32
2,000...................................................              40
2,500...................................................              45
3,000...................................................              52
3,500...................................................              57
4,000...................................................              62
4,250...................................................              65
------------------------------------------------------------------------
\a\ These design frost depths are intended to be used for protection of
  building foundations against frost heave and are not applicable to
  site or street utilities or other non-building applications.
\b\ These design frost depths for footings shall be permitted to be
  halved for footings interior to the building perimeter and located
  within an enclosed space. Where skirting is used to enclose the space,
  the skirting shall be insulated to a minimum R-5 (1,000 to 2,500 AFI)
  or R-10 (>2,500 AFI) and vents shall be capable of closing at outdoor
  temperatures below 40 [deg]F (which necessitates use of a ground vapor
  barrier).

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Option #2: Checklist for Monolithic Slab Systems in Freezing 
Temperature Areas

HUD Code, 24 CFR 3285.312(b)(2)
    Pre-Installation Preparations:
     Before initiating installation, verify that the 
installation instructions are designed (sealed) by a registered 
professional engineer or registered architect, and approved by the 
manufacturer and its DAPIA.
     When applicable, verify that the LAHJ has accepted and 
approved the foundation and installation plan and all applicable 
permits are obtained. For designs that rely on well-drained sites and 
use of existing soils to frost depth that are non-frost susceptible, 
verify the following before initiating installation:
    [cir] The non-frost-susceptible condition of existing soils above 
the frost depth and below the base of the slab at each site has been 
verified by site soil records or tested by a soils engineer or 
geologist or tested in accordance with ASTM D422 and determined to have 
a fines mass content of less than 6% by mass passing a #200 sieve for 
the specific installation site or the development as a whole. A soils 
report should be provided by the engineer or soil lab of record for 
verification.
    [cir] Alternatively, conduct such testing as follows:
    [rtarr8] Obtain a minimum of two soil samples per installation site 
(one at each end of the foundation area) and from any borrow materials 
on site used as fill. A materials report from a quarry may be used when 
material is supplied from a licensed quarry.
    [rtarr8] When conducting borings for soil samples, take a minimum 
of one pint (plastic bag full) of soil from depths of one foot and at 
the determined frost depth or at the frost depth as determined from 
Table 1, Design Frost Depth for Footings. Continue each boring to two 
feet below the determined frost depth (as measured from the proposed 
finish grade) to determine if the water table is present.
    [rtarr8] Deliver or send the soil samples to a soils laboratory for 
particle size testing per ASTM D422.
    [rtarr8] If the soils laboratory report indicates greater than 6% 
fines by mass passing a #200 sieve, then the soil at the site is frost 
susceptible and either footing to frost depth or one of the alternative 
foundation options (see https://portal.hud.gov/hudportal/documents/huddoc?id=10-07-16-Frost-free-Found.pdf) for frost susceptible soil 
conditions should be used.
    [cir] The water table condition of the site has been assessed by 
the engineer or architect of record and documentation provided of the 
water table being at least two feet below the determined frost depth. 
Alternatively, make this determination using soil borings as described 
above.
    [cir] If the water table is higher than two feet below the 
determined frost depth, a network of drainage pipes sloped to drain to 
daylight or an engineered drainage system must be placed at the base of 
non-frost-susceptible fill (e.g., clean gravel or crush rock) placed to 
a depth equal to the local frost depth.
    [cir] Alternatively, a site specific foundation design can be 
prepared and sealed by a professional engineer or registered architect 
or geologist and approved by the manufacturer and its DAPIA. Such 
foundation designs are to comply with the provisions of the ASCE 32 
Standard or with accepted engineering practice that will result in 
comparable performance to the frost protection afforded by the ASCE 32 
Standard.
    [cir] Save documentation of all of the above and provide to the 
LAHJ for verification as required.
     For designs that rely on well-drained sites and use of 
fill materials to frost depth that are non-frost susceptible, verify 
the following before initiating installation:
    [cir] The slab base and foundation fill materials are specified by 
the engineer or architect of record as non-frost susceptible such as 
clean gravel or crushed rock or other suitable material with no more 
than 6% fines by mass passing a #200 sieve per ASTM D422 test method. 
Non-frost susceptible subgrade materials are to be filled from the 
frost depth to the slab base for the entire extent of the slab plus any 
over dig.
    [cir] The water table condition of the site has been assessed by 
the engineer or architect of record and documentation provided of the 
water table being at least two feet below the determined frost depth. 
Alternatively, this determination can be made using soil borings as 
described above.
    [rtarr8] If the water table is higher than two feet below the 
determined frost depth, a network of drainage pipe sloped to drain to 
daylight or an engineered drainage system should be placed at the base 
of non-frost-susceptible fill (e.g., clean gravel or crush rock) placed 
to a depth equal to the determined frost depth.
    [cir] Save documentation of all of the above and provide to the 
LAHJ for verification as required.
    Installation Phase:
     Excavate slab area to frost depth or only to the bottom of 
the slab's non-frost-susceptible base layer if existing soils have been 
determined to be non-frost susceptible down to frost depth during the 
pre-installation preparation phase (see above).
     Place foundation drains sloped to drain to daylight or an 
engineered drainage system at the bottom of the non-frost-susceptible 
base or fill material layer.
     Place the non-frost-susceptible fill and base materials, 
compacting as required by the manufacturer's installation instructions 
and/or the engineer or architect of record. Do not initiate fill 
placement where compaction requirements and methods are not specified. 
Obtain compaction requirements, as needed, from the engineer or 
architect of record. The minimum requirement is 90% compaction per 24 
CFR 3285.201 although the engineer or architect of record or LAHJ may 
require a higher compaction level based on the fill material used.
     Construct the reinforced monolithic slab in accordance 
with the manufacturer's installation instructions or according to the 
manufacturer and DAPIA approved installation instructions and plans.
     Backfill as needed and grade the site as required for 
drainage:
    [cir] Slope grade a minimum of \1/2\-inch per foot for a minimum 
distance of 10 feet away from the home perimeter.

Option #3: Checklist for Frost Protected Shallow Foundations (Insulated 
Foundations)

HUD Code, 24 CFR 3285.312(b)(3)
    Pre-Installation Preparations:
     Before initiating installation, verify that the 
installation instructions are designed (sealed) and certified by a 
registered professional engineer or registered architect, approved by 
the manufacturer and its DAPIA.
     Also, verify that the instructions include an approved 
installation design complying with one of the following bases for the 
proposed installation design, as permitted in the HUD Code:
    [cir] Complies with acceptable engineering practice or the ASCE 32 
standard by use of properly-specified insulation materials and sized in 
accordance with the local temperature area and located around the 
perimeter of the foundation with insulated skirting and closeable vents 
or the entire foundation pad is insulated where there is no skirting or 
the skirting is not insulated or the skirting has non-closing vents. 
Non-frost-susceptible base materials are used at a minimum thickness 
required by acceptable engineering practice or SEI/ASCE 32, and 
insulation materials are protected

[[Page 28287]]

against damage in accordance with acceptable engineering practice or 
ASCE 32.
    [cir] Complies with acceptable engineering practice to prevent the 
effects of frost heave in accordance with acceptable engineering 
practice or in a manner equivalent to the insulation provisions in the 
ASCE 32 standard.

    Note: Designs which place insulation materials in a 
discontinuous fashion, such that exposed slab edges or other types 
of thermal bridging occurs, do not meet the requirements of the SEI/
ASCE 32 standard or the HUD Code provisions that allow the use of 
``acceptable engineering practice to prevent the effects of frost 
heave.''

     Obtain foundation insulation materials as specified in the 
installation instruction and verify the correct type is received. 
Commonly accepted insulation materials include Extruded Polystyrene 
(XPS) and Expanded Polystyrene (EPS) of various ``types'' in accordance 
with ASTM C578 and ASCE 32 standards.
     Insulation material conformance with the specified type 
should be verified by product labels or a certification from the 
insulation manufacturer. Materials commonly stocked in supply stores 
may not be the correct ``type'' even though it may be the correct 
``kind'' (e.g., XPS or EPS).

    Note: There is no need to determine the frost susceptibility of 
underlying soils to frost depth in the insulated foundation design 
approach when the foundation and ground insulation provisions of 
ASCE 32 are satisfied.

    Installation Phase:
     Excavate the foundation area to the correct shallow 
foundation depth as indicated in the manufacturer's installation 
instructions or by the engineer or architect of record (generally the 
foundation depth need not exceed 12'' to 16'' below finish grade).
     Place specified non-frost-susceptible base material and 
provide drainage pipes around the perimeter, at a minimum of 4 inches 
(within the base material layer) as required by the installation 
instructions. Pipes need to be run to day-light or have a mechanical 
means of draining the water. Sequence the foundation slab or pad 
construction and insulation placement in accordance with the design 
approach indicated on the manufacturer's installation instructions. 
Where sub-slab insulation is required, this will need to be placed 
before slab construction. Perimeter insulation may be placed after slab 
construction.
     After construction of the slab and supports and placement 
of the home, construct the insulated skirting with closeable vents as 
required by the manufacturer's installation instructions. Where the 
foundation slab is entirely insulated with horizontal below ground 
insulation (the design does not rely on perimeter insulation only), no 
skirting is required.
     Place wing insulation (extending outward horizontally 
underground from the perimeter of the foundation) as required by the 
installation instructions. Depending on the design approach and 
temperature severity, wing insulation may or may not be required.
     Provide protection of any exposed exterior insulation or 
within 10 inches of the finish grade surface.
     Backfill as needed and grade the site as required for 
drainage:
    [cir] Slope grade a minimum of \1/2\-inch per foot for a minimum 
distance of 10 feet away from the home perimeter.

Option #4: Checklist for Alternative Foundations on Non-Frost 
Susceptible Soils Including Frost Free Foundations

HUD Code, 24 CFR 3285.2
    Pre-Installation Preparations:
     Before initiating installation, verify that the 
installation instructions are designed (sealed) by a professional 
engineer or registered architect, and approved by the manufacturer and 
its DAPIA. The LAHJ can require that the plans also be reviewed and 
sealed by an engineer or architect in the state where the installation 
is to occur.
     When applicable, verify that the LAHJ has accepted and 
approved the alternative foundation and installation plan and all 
applicable permits are obtained. The installation design needs to 
comply with one of the following conformance options for the proposed 
installation design as permitted in HUD's Model Manufactured Home 
Installation Standards:
    [cir] Complies with acceptable engineering practice or the ASCE 32 
standard by use of non-frost-susceptible site soils or fills 
(adequately tested and verified as defined in ASCE 32) and that such 
soils or fills extend to the determined frost depth with provision for 
adequate surface and subgrade drainage especially where underlying 
soils are poorly drained and/or the water table is within two feet of 
the design frost depth.

    Note: Reliance solely on surface drainage to prevent the effects 
of frost heave without verification of non-frost-susceptible fill 
materials or existing non-frost susceptible soils to frost depth 
does not comply with the design principles of the ASCE 32 standard 
or HUD Code's allowance for ``acceptable engineering practice to 
prevent the effects of frost heave.''

     For designs that rely on well-drained soils and sites and 
use of existing soils to frost depth that are non-frost susceptible, 
verify the following before initiating installation:
    [cir] The non-frost-susceptible characteristic of existing soils 
above the determined frost depth at each site has been tested by a 
soils engineer or geologist or tested in accordance with ASTM D422 and 
determined to have a fines mass content of less than 6% passing a #200 
sieve for the specific installation site or the development as a whole. 
A soils report should be provided by the engineer or soil lab of record 
for verification.
    [cir] Alternatively, conduct such testing as follows:
    [rtarr8] Obtain a minimum of two soil samples per installation site 
(one at each end of the foundation area) and from any borrow materials 
on site used as fill. A materials report from a quarry may be used when 
material is supplied from a licensed quarry.
    [rtarr8] When conducting borings for soil samples, take a minimum 
of one pint (plastic bag full) of soil from depths of one foot and at 
the determined prescribed frost depth or as determined from Table 1, 
Design Frost Depth for Footings. Continue each boring to two feet below 
the determined prescribed frost depth (as measured from the proposed 
finish grade) to determine if the water table is present.
    [rtarr8] Deliver or send the soil samples to a soils laboratory for 
particle size testing per ASTM D442.
    [rtarr8] If the soils laboratory report indicates greater than 6% 
fines by mass passing a #200 sieve, then the soil at the site is frost 
susceptible and either a footing to frost depth or a manufacturer and 
DAPIA approved alternative foundation for frost susceptible soil 
conditions must be used.
    [cir] The water table condition of the site has been assessed by 
the engineer or architect of record and documentation provided of the 
water table being at least two feet below the determined frost depth. 
Alternatively, make this determination using soil borings as described 
above.
    [cir] If the water table is higher than two feet below the 
determined frost depth, a network of drainage pipes sloped to drain to 
daylight or an engineered drainage system should be placed at the base 
of non-frost-susceptible fill (e.g., clean gravel or crush rock) placed 
to a depth equal to the determined frost depth.
    [cir] Alternatively, a site specific foundation design can be 
prepared and sealed by a professional engineer or registered architect 
or geologist and

[[Page 28288]]

approved by the manufacturer and its DAPIA. Such Foundation designs are 
to comply with the provisions of the ASCE 32 Standard or with accepted 
engineering practice that will result in comparable performance to the 
frost protection afforded by the ASCE 32 Standard.
    [cir] Save documentation of all of the above and provide to the 
LAHJ for verification as required.
     For designs that rely on well-drained sites and use of 
fill materials to frost depth that are non-frost susceptible, verify 
the following before initiating installation:
    [cir] The slab base and foundation fill materials are specified by 
the engineer or architect of record as non-frost susceptible such as 
clean gravel or crushed rock or other suitable material with no more 
than 6% fines by mass passing a #200 sieve per ASTM D442 test method. 
Non-frost susceptible subgrade materials are to be filled from the 
frost depth to the slab base for the entire extent of the slab plus any 
over dig.
    [cir] The water table condition of the site has been assessed by 
the engineer or architect of record and documentation provided of the 
water table being at least two feet below the determined frost depth. 
Alternatively, this determination can be made using soil borings as 
described above.
    [rtarr8] If the water table is higher than two feet below the 
determined frost depth, a network of drainage pipe sloped to drain to 
daylight or an engineered drainage system should be placed at the base 
of non-frost-susceptible fill (e.g., clean gravel or crush rock) placed 
to a depth equal to the local frost depth.
    [cir] Save documentation of all of the above and provide to the 
LAHJ for verification as required.
    Installation Phase:
     Excavate area under foundation or slab to frost depth or 
only to the bottom of the non-frost-susceptible base layer if existing 
soils have been determined to be non-frost susceptible down to frost 
depth during the pre-installation preparation phase (see above).
     Place foundation drains sloped to drain to daylight or an 
engineered drainage system at the bottom of the non-frost-susceptible 
base or fill material layer.
     Place the non-frost-susceptible fill and base materials, 
compacting as required by the manufacturer's installation instructions 
and/or the engineer or architect of record. Do not initiate fill 
placement where compaction requirements and methods are not specified. 
Obtain compaction requirements, as needed, from the engineer or 
architect of record. The minimum requirement is 90% compaction per 24 
CFR 3285.201 although the engineer or architect of record or LAHJ may 
require a higher compaction level based on the fill material used.
     Construct the alternative foundation system in accordance 
with the manufacturer's installation instructions or according to the 
manufacturer and DAPIA approved installation instructions and plans.
     Backfill as needed and grade the site as required for 
drainage:
    [cir] Slope grade a minimum of \1/2\-inch per foot for a minimum 
distance of 10 feet away from the home perimeter.

    Note: The above procedures also apply to designs where a 
monolithic slab is not used and pier footing pads are placed 
directly on non-frost-susceptible soils or fill materials (e.g., 
clean gravel or crushed rock) to the determined frost depth.

    This Interpretative Bulletin is issued pursuant to 24 CFR 3285.2 
and 3285.312(b) of HUD's Model Manufactured Home Installation 
Standards.

    Dated: June 15, 2017.
Genger Charles,
General Deputy Assistant Secretary for Housing.
[FR Doc. 2017-12964 Filed 6-20-17; 8:45 am]
 BILLING CODE 4210-67-P