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t
Factors to Consider in Design
Proprietary Foundation and Support Systems
Non-proprietary Foundation and SupportSystems
DRAFT – Not for Distribution
U.S. Department of Housingand Urban Development Office of Policy Developmenand Research
PATH (Partnership for Advancing Technology in Housing) is a private/public effort to develop, demonstrate, and gain widespread market acceptance for the next generation of American housing. Through the use of new or innovative technologies the goal of PATH is to improve the quality, durability, environmental efficiency, and affordability of tomorrow’s homes.
PATH is managed and supported by the U.S. Department of Housing and Urban Development (HUD). In addi tion, all Federal Agencies that engage in housing research and technology development are PATH partners including the Departments of Energy and Commerce, as well as the Environmental Protection Agency (EPA) and the Federal Emergency Management Agency (FEMA). State and local governments and other participants from the public sector are also partners in PATH. Product manufacturers, home builders, insurance compa nies, and lenders represent private industry in the PATH partnership.
To learn more about PATH, please contact:
451 Seventh Street, SW Washington, D.C. 20410 202-708-4250 (phone) 202-708-5873 (fax) e-mail: pathnet@pathnet.org
www.huduser.org
The Manufactured Housing Research Alliance wishes to acknowledge the assistance, advice, and guidance of a number of people without whose help this publication would not have been possible.
The effort was lead by a project steering committee: Bill Farish, Fleetwood Enterprises , Project Chair Ed Bryant, Champion Enterprises Charles Fanaro, Hi-Tech Housing Bill Freeborne, U.S. Department of Housing and Urban Development James Reitzner, Asset Development Group Andrea Vrankar, U.S. Department of Housing and Urban Development Roger Walker, Ventana Development, LLC Frank Walter, Manufactured Housing Institute
Other industry representatives whose advice and guidance helped shape the guide: Gary Austin, Mobile Corral Homes, Inc. J.R. Bader, Mausten Home Sales David Conover, National Evaluation Service Pamela B. Danner, Danner and Associates Brian Fannon, Sun Communities Siavash Farvardin, National Evaluation Service Doug Gorman, Home Mart John Ingargiola, Federal Emergency Management Agency Therese P. McAllister, Greenhorne & O'Mara Barry McCabe, Hometown America Communities Gary McDaniel, Chateau Communities Rick Mendlen, U.S. Department of Housing and Urban Development George Porter, Manufactured Housing Resources Roger Wendt, Sunrise Home Service
Companies that submitted designs or product information: The Anchor Post Company, LLC Asset Development Group Chateau Communities Cherry Hill Homes CWS Communities Fast Track Foundation Systems Fleetwood Homes Goff's Fleetwood Home Center Jensen's, Inc. JM Products, Inc Oliver Technologies, Inc. Roger Huddleston Manufactured Homes Tie Down Engineering Ventana Development, LLC
Design, production, and editorial subcontractors: Hoi L. Chu, HLC Group Dorothy Foster Jennifer Goode Robert LaPointe
MHRA staff responsible for coordinating and facilitating development of the guide: Emanuel Levy, Executive Director Ed Salsbury, Project Coordinator Sandra Ho, Editorial Director Ian Klose, Staff Kathleen Boodoo, Staff
Neither the authors, nor reviewers, nor the U.S. Department of Housing and Urban Development, nor the Manufactured Housing Institute, nor the Manufactured Housing Research Alliance, nor any of their employees or representatives makes any warranty, guarantee, or representation, expressed or implied, with respect to the accu racy, effectiveness, or usefulness of any information, method, or material in this document, nor assumes any lia bility for the use of any information, methods, or materials disclosed herein, or for damages arising from such use. This publication is intended for the use of professional personnel who are competent to evaluate the significance and limitations of the reported information and who should accept responsibility for the application of the material it contains. All responsibility as to the appropriate use of information in this document is the responsibility of the reader or user.
The contents of this report are the view of the contractor and do not necessarily reflect the views or policies of the U.S. Department of Housing and Urban Development or the US government.
Neither the U.S. government, nor MHRA endorse products or manufacturers. Trade or manufacturer's names that appear herein are used solely because they are considered essential to the objective of the report. Companies that appear in Chapter 4 paid a fee to include their material in the guide. Other foundation suppliers that MHRA was aware of are listed at the end of Chapter 4. All manufacturers are welcome to participate in future versions of the guide. Any claims made by a company were not independently verified by MHRA and makes no representation or warranties of any kind, either express or implied, including but not limited to warranties of title, noninfringement or implied warranties of merchantability or fitness for a particular purpose and expressly disclaims any liability with respect to the content or accuracy of this information. This is not a consumer report. There is no relative ranking of systems.
MHRA does not endorse, certify or control the foundation systems presented as case studies in Chapter Three or the company proprietary foundation systems presented in Chapter Four. The views and opinions of the companies expressed in Chapter Four do not necessarily state or reflect those of MHRA, and shall not be used for advertising or product endorsement purposes. MHRA does not guarantee the accuracy, completeness, currency or reliability of the information submitted by the companies concerning their proprietary foundation systems. The information obtained from this guide is provided without warranties of any kind, either express or implied, including but not limited to warranties of title, noninfringement or implied warranties of merchantability or fitness for a particular purpose. The use of any information contained in these materials is voluntary, and reliance on it by the user should be under taken after an independent review of its accuracy, completeness, currency and reliability.
The systems included in this guide are representative of the systems MHRA was aware of at the time of publication. MHRA does not imply that these are all of the systems that exist.
For several decades, manufactured homes built to the preemptive Federal Manufactured Home Construction and Safety Standards have been the nation's foremost source of unsubsidized affordable housing. Until relatively recently, the majority of manufactured homes were economical single section designs, financed with asset-backed loans, sold most often to first-time home buyers and seniors and located in suburban and rural settings. Manufactured homes were also distinguished from their site-built counterparts in the way they were secured to the ground—the majority are held in place by pier and anchor systems.
Within the last five years, the manufactured housing industry has experienced an evolution and the rate of change appears to be accelerating. Sales of multisection homes have well-outpaced single-section designs, the popularity of land/home financing continues to grow, the buyer demographics are diversifying, and new markets are opening to manufactured homes, particularly in urban infill and higher density areas.
Homes built in compliance with the HUD standards are entering the portfolio of developers that have historically used site-building methods exclusively. The economics of building homes in a factory under a single national code has long been attractive. But only in the last few years has the vision of manufactured homes as a technology for supplying a wider range of affordable housing needs begun to be realized.
The changes in the manufactured housing market, the evolution of the industry itself and the diversification of the potential customers for manufactured homes are ushering in a host of innovations and changes to the industry's core product. No area is more affected by these changes than the methods for supporting and fastening the home to the ground.
This guide serves several functions. First, it helps decision makers in formulating a strategy for sorting among foun dation and support system alternatives and describes factors that impact the design and construction process. Second it exposes the manufactured housing industry, buyers of manufactured homes and others interested in HUD-code housing to some of the more popular and practical ways of designing and installing manufactured home foundation or support systems. These designs are springboards for exploring alternative design approaches and solutions. Lastly, through the use of case studies, the guide examines how some practitioners are already pursing new foundation and support system methods, hinting at the wealth and diversity of foundation solutions yet to come.
Lawrence L. Thompson
General Deputy Assistant Secretary for Policy Development and Research
CONTENTS
A. B. C.
Chapter 1 Executive Summary 1.
Chapter 3 Individual Foundation Evaluations: Non-Proprietary Systems 3.
Chapter 4 Individual Foundation Evaluations: Proprietary Systems 4.
Chapter 2 Factors to Consider in Foundation Selection and Design 2.
Appendices
Using the Guide ix
Why a Foundation and Support Systems Guide Purpose of the Guide How the Guide is Organized What the Words “Real Property Foundation” Mean What the Words “FHA Permanent Foundation” Mean
Site Conditions Major Design Factors Best Design Practices
Pier and Ground Anchor Support Systems Crawl Space Systems Case Study 1: Mt. Clemens, MI Case Study 2: Williamston, KY Case Study 3: Longmont, CO Case Study 4: Campbellsville, KY Case Study 5: Mahomet, IL Case Study 6: Mahomet, IL Case Study 7: Fond du Lac, WI Case Study 8: Kansas City, MO Case Study 9: Germantown, WI Slabs-on-Grade Case Study 10: Milwaukee, WI Case Study 11: Eau Claire, WI Case Study 12: Hyde Park, MD Basements Case Study 13: Mahomet, IL Case Study 14: Elizabethtown, PA
All Steel Foundation System, Oliver Technologies, Inc. The Anchorpanel Foundation, Fast Track Foundation Systems Rigid Foundation Anchoring System, JM Products, Inc. The Storm Anchor System, The Anchor Post Company, LLC Vector Dynamics Foundation System, Tie Down Engineering Xi Foundation System, Tie Down Engineering Other Proprietary Foundation System Suppliers
A. Glossary B. References C. Additional Resources
Table I.
Foundation System Type Initial Cost 1
Real Property Foundation^2
Installation Time 3
Use in Seismic Areas
Use in Flood Hazard Areas^4
Use in Areas Subject to Frost Heave Page No. See Page 2.10^ See Page 1.3^ See Page 2.10^ See Page 2.7^ See Page 2.5^ See Page 2. NON-PROPRIETARY FOUNDATION SYSTEMS Pier and Ground Anchors
PROPRIETARY FOUNDATION SYSTEMS^5 The All Steel Foundation
The Anchorpanel Foundation,
Rigid Foundation Anchoring
The Storm Anchor System,
Vector Dynamics,
Xi Foundation, Tie Down Engineering
(^1) The symbols in this column are intended to suggest the relative magnitude of initial system costs, not absolute dollar figures. Initial costs are ranked from least ($) to most ($$$$) costly. As with any rating method, individual designs may be exceptions to these relative placements.
(^2) The designation shown for non-proprietary real foundation systems is a general guideline. Such designation is subject to the manufacturer's verification and not all designs may qualify as a real property foundation. Real property foundation designations for proprietary foundation sys tems were determined by the companies that supply those products and have not been independently verified. Whether a manufactured home may be classified as real property is determined by state or local laws.
(^3) The symbols in this column are intended to suggest the relative time required to install the foundation or support system, not absolute instal lation times. Installation costs are ranked from requiring the least amount of time ( (^) ¥ ) to the most amount of time ( (^) ¥ ¥ ¥ ) to install. As with any rating method, individual designs may be exceptions to these relative placements.
(^4) For use in flood hazard area, the lowest floor of a manufactured home shall be elevated to or above the base flood elevation (BFE) and be securely anchored to an adequately anchored foundation system to resist flotation, collapse, and lateral movement (44 CFR 60.3 (c)(6), with a 36-inch pier height exception rule for existing communities, at 60.3 (c)(12)(ii)—FEMA—National Flood Insurance Program.)
(^5) Entries for the proprietary foundation systems are provided by the companies themselves and are not independently verified.
x
The term "foundation" means all components of the support and anchoring system (that might include such features as piers, footings, slabs, walls, ties, anchoring equipment, ground anchors, or any other material or equipment) that supports a home and secures it to the ground.^6
For as many types and varieties of manufactured homes as are now produced—with more to come—there are equally as many varieties of installation and support systems. This is the first guide to consider and compare the major foundation alternatives in use across the country. This guide was developed to fill this void with two goals in mind: to present a compilation of foundation ideas and inventions culled from experts and practitioners across the nation; and, to offer a range of practical and cost-competitive foundation solutions.
There is no single "best" foundation system. There is, however, a way to organize the process of deciding among alternative founda tion designs that are appropriate for a given site and budget. The process starts with recog nizing and prioritizing the major factors that influence the selection of the foundation system. Whether the main considerations are initial cost, frost heave resistance or a host of other issues, this information will help the reader focus on an appropriate foundation design. Understanding the foundation alterna tives and proven design and installation prac tices is the next step. By presenting both sets of information, this guide helps narrow the field among many options and establish a methodical process for decision making.
Users of this guide should find practical and helpful solutions to their individual situations. Whether the reader is a retailer trying to find better and more economical ways to deliver a finished home, a contractor faced with an unusual soil condition, or anyone wanting to better understand the alternatives, suggestions can be found in this guide. There are summaries and tables for quickly identifying appropriate foundation systems for a particular site and homebuyer, as well as technical details for direct application to the project at hand.
The guide is intended to be instrumental in fostering the wider dissemination of good ideas and "out of the box" thinking that characterizes the manufactured housing industry in general.
Each system included in this compilation suggest advantages in at least some settings. Comments about the pros and cons, as well as the special limitations of each system, are included.
When deciding among alternatives, several key conditions and objectives should be considered, such as: What is the budget? What kind of financing will be sought? What type of soil is found at the site? Is the area subject to frost?
(^6) Depending on the context and application, the means for anchoring, supporting and otherwise securing a manufactured home to the ground is referred to as either the support system or foundation system. For simplicity, the term "foundation system" is used throughout this guide and should be interpreted broadly as including support and foundation systems.
Figure 1.1 Crane set of a multi-section home on to a basement.
1.
A non-proprietary system is considered to be "in the public domain"—usable by anyone without paying a royalty, fee, or other consideration for its use. It is not a product of manufacturing or individual company output. Non-proprietary systems can be con structed by any qualified contractor, using materials available from most building suppliers.
Included in each foundation class are a series of case studies drawn from actual installations and contributed by practitioners from across the nation. The case studies suggest how a basic concept can be modified to meet the specific needs of a site, home design, or buyer preference.
This section contains information about several proprietary foundation products marketed to the manufactured housing industry. A proprietary system is a product, manufactured by a company that owns some protectable interest in the design. Some are patented. There is spirited competition among manu facturers of these proprietary systems, resulting in rich choices for the retailer, builder, contractor and homebuyer.
The information contained in this section was prepared by the companies themselves. The following products and companies are represented:
Because of the rapid pace of advances in the manufactured housing industry, many customary and industry and phrases have changed or taken on new meanings. This is especially true when the subject is foundation systems.
For example, the manufactured home is the only type of residential dwelling intended to be used as either personal or "real property." Manufacturers often establish a special set of conditions for foundation systems intended for use with homes financed as real property with a mortgage or deed of trust. The techniques for supporting homes financed as either real or personal property are intended to result in properly engineered and reliable foundation systems. Whether used with real property or personal property, all foundation systems including those in this guide, are meant to be safe, durable and long lasting.
Nothing in this guide is intended to suggest that a home on any particular foundation system is or is not real prop erty rather than personal property. In all cases, real or personal property status is determined by state or local laws that may or may not reference foundation type. Similarly, eligibility for conventional long-term financing is deter mined by underwriting standards that may or may not reference the foundation type or real versus personal property status.
Figure 1.3 Some foundations use a combination of interior piers and perimeter walls to support the home.
Figure 1.4 Some foundations are recessed to create a "site-built" look.
1.
The U.S. Department of Housing and Urban Development (HUD), Federal Housing Administration (FHA), defines per manent foundation systems as follows:
"Permanent foundations must be constructed of durable materials; i.e., concrete, mortared masonry, or treated wood-and be site-built. It shall have attachment points to anchor and stabilize the manufactured home to transfer all loads, herein defined, to the underlying soil or rock. The permanent foundations shall be structurally developed in accordance with this document or be structurally designed by a licensed professional engineer for the following:
a. Rated anchorage capacity to prevent uplift and overturning due to wind or seismic forces, whichever controls. Screw-in soil anchors are not considered a permanent anchorage.
b. Footing size to prevent overloading the soil-bearing capacity and avoid soil settlement. Footing shall be reinforced concrete to be considered permanent.
c. Base of footing below maximum frost-penetration depth.
d. Encloses a basement of crawl space with a continuous wall (whether bearing or non-bearing) that separates the basement of crawl space from the backfill, and keeps out vermin or water.
It is beyond the scope and purpose of this guide to assess whether a particular foundation system meets this defini tion of performance, and would likely qualify for FHA Title II insurance. This is the responsibility of the FHA and its representatives. However, this guide contains useful information that the professional and consumer may want to consider in determining the appropriate foundation system to be used for a given installation.
Nearly 30 years ago when HUD adopted the nationally preemptive manufactured home standards, the stage was set for the explosive growth of the nation's primary source of unsubsidized affordable housing. The information con tained in this guide is intended to complement and affirm this preemptive mandate and help the industry to con tinue to meet the nation's ever diversifying housing needs.
(^7) U.S. Department of Housing and Urban Development. 1996. Permanent Foundations Guide for Manufactured Housing. HUD-007487. September 1996. Questions regarding whether or not a system qualifies under this definition can be referred to the U.S. Department of Housing and Urban Development, Office of Consumer and Regulatory Affairs, 451 7th St. S.W., Room 9156, Washington, DC 20410, phone: (202) 708-6409.
1.
Table 2.1 The Properties of Soil
Soil Description
Value as a foundation material
Drainage characteristics^8
Susceptibility to frost heave
Volume change potential expansion^9
Well-graded gravels, gravel-sand mixtures, little or no fines Excellent^ Good^ Low^ Low
Poorly graded gravels or gravel- sand mixtures, litttle or no fines Good^ Good^ Low^ Low Well-graded sands, gravelly sands, little or no fines Good^ Good^ Low^ Low
Poorly graded sands or gravelly sands, little or no fines Good^ Good^ Low^ Low
Silty gravels, gravel-sand-silt mixtures Good^ Good^ Medium^ Low
Clayey gravels, gravel-sand-clay mixtures Good^ Medium^ Medium^ Low
Silty sand, sand-silt mixtures Fair Good Medium Low
Clayey gravels, sand-clay mixture Fair^ Medium^ Medium^ Low
Inorganic silts and very fine sands, rock flour, silty or clayey fine sands or clayey silts with slight plasticity
Fair Medium (^) High Low
Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays, lean clays
Fair Medium (^) Medium Medium tolow
Inorganic silts, micaceous or diatomaceous fine sandy or silty soils, elastic silts
Poor (^) Poor High High
Organic silts and organic silty clays of low plasticity Poor^ Poor^ Medium^ Medium
Inorganic clays of high plasticity, fat clays Very Poor^ Poor^ Medium^ High
Organic clays of medium to high plasticity, organic silts Very Poor^ Unsatisfactory^ Medium^ High
Peat and other highly organic soils Not suitable Unsatisfactory (^) Medium High
SOURCE: 2000 International Residential Code ®
(^8) The percolation rate for good drainage is over 4 in. per hour, medium drainage is 2 to 4 in. per hour, and poor is less than 2 in. per hour.
(^9) Soils with a low potential expansion typically have a plasticity index (PI) of 0 to 15, soils with a medium potential expansion have a PI of 10 to 35, and soils with a high potential expansion have a PI greater than 20.
2.
One important measure of the ability of soil to support the weight of the home is its bearing capacity, a value repre senting the weight that one sq ft of earth surface is capable of supporting without risk of subsiding. This information may already be available from the local building department or from a local engineer. Values range from less than 1,000 lbs per square foot (psf) to more than 4,000 psf.
Other problems can arise when foundation systems are placed on soils that contain a high percentage of organic matter or on fill soil. Excessive organic matter should be removed and fill properly compacted.
Special mention should be made of a broad group of "expansive" soils. Expansive soils significantly change volume as they absorb water. Highly active soils (see Figure 2.2 ) are particularly prone to shifting as water content rises and falls. Special building practices have been developed for homes located in areas with expansive soils. These are areas where local engineers should be consulted before designing a foundation system. Slabs-on-grade founda tion systems are often desirable in areas with expansive soils.
Areas with extensive regions with highly active soils
Areas with extensive regions with less active soils
Areas with soils that are predominantly not active
Figure 2.2 Map of Expansive Soil Regions
NOTE: In areas of the map with highly active soils, there will be many locations with no expansive soils. Conversely, in the areas of the map with the least active soils, expansive soils can be found in some locations. SOURCE: Oak Ridge National Laboratory (ORNL) Building Foundation Design Handbook, 1988.
2.
Unless proper precautions are taken, homes located in low-lying sites near waterways or along the coasts are at risk of flood damage. Riverine flooding takes place when excessive runoff causes a stream or river to overflow its normal channel. Coastal flooding normally is the result of ocean storms, which can be severe.
Flood hazard areas are referred to as flood plains. Flood plains, outside the floodway, may become inundated with rising water that has little or no movement. It is possible to minimize or eliminate the risk of damage to homes located in the flood plain. A flood plain may, however, contain floodways, an identified area where the risk of damage from moving water and the debris that it may carry is so great that it prohibits residential construction.
The first step when dealing with a building site within a flood plain is to verify that it is outside of the floodway. The Federal Emergency Management Agency (FEMA) and its local flood plain administrator are the best sources of infor mation regarding the history of local floods and potential for flood damage.^12
In addition to identifying areas subject to varying degrees of flood severity, FEMA's flood maps are used to deter mine zones for National Flood Insurance Program (NFIP) premium rates. In a flood plain, the lowest floor is located at or above the Base Flood Elevation (BFE). The BFE, also referred to as "100-year flood" level, is indicated on the Flood Insurance Rate Map (FIRM) available from the local FEMA administrator. FEMA's flood maps indicate the areas where the land is below the BFE. New homes installed with the first floor (including a basement floor) below the BFE are ineligible for the NFIP rates (certain exceptions apply; consult 44 CFR 60.3, local flood plain ordinance). In most cases, homes below the BFE ineligible for any form of federally supported financing and other types of disaster assistance.
If properly designed, crawl space foundation systems can be used in flood plains. Other suitable foundation sys tems include reinforced piers and pile foundation systems. Basements, by definition, involve substantial excavation and the creation of below-grade living areas. This automatically disqualifies them from participating in the NFIP. Finally, slabs may be acceptable, assuming the home itself is sufficiently elevated above the ground.^13
(^11) For more information refer to Myers, Ned C. 1996. Manufactured Home Foundation Design for Seasonally Frozen Ground.
(^12) Maps denoting flood areas are available from the FEMA flood map repository. The maps can be ordered by calling: (800) 358-9616, or by visiting the map order web site at: www.msc.fema.gov/MSC/product.htm.
(^13) For more information about building in the flood plain, consult 44 CFR 60.3, local flood plain ordinance, and FEMA guidelines, including Manufactured Home Installation In Flood Hazard Areas, FEMA 85 (September 1985). As this guide goes to press, FEMA is in process of revising and updating the FEMA 85 document.
2.
The southeast coast of the United States is prone to tropical storms and hurricanes. Foundation design and selec tion in these areas is often subject to local code wind speed minimums (see Figure 2.5 ). Where hurricanes are common, the selection of a foundation system must take into consideration its ability to hold a home down in hurri cane winds.
80
Basic wind speed 70 mph (fastest mile)
Special wind region
80
(^70 ) 80 80
70
(^70 )
90
(^9090) 90
(^7090)
70
110
110
110 110 100 90 90
80
100
100
110
110
110 110
70
70
90
NOTES:
Figure 2.5 Basic Wind Speed Map (fastest wind speed, mph)
2.
