PROTECTING MANUFACTURED HOMES FROM FLOODS AND OTHER HAZARDS 
A Multi-Hazard Foundation and Installation Guide
FEMA P-85, Second Edition, November 2009


PREFACE

The Federal Emergency Management Agency (FEMA) first published 
Manufactured 
Home Installation in Flood Hazard Areas (FEMA 85) in 1985. Since then, 
manufactured homes have become better built, and natural hazards like 
flood, 
wind, and earthquake (seismic) events are better understood. 

To benefit from the advances made in the last 24 years, FEMA 85 has been 
updated to reflect the requirements of the most current codes and 
standards 
and to provide a best practices approach in reducing damages from natural 
hazards. While the original version of FEMA 85 concentrated on flood and 
wind 
events, this version also addresses seismic hazards and recommends several 
multi-hazard resistant foundation designs. Designs are included for wood-
framed foundations, conventional concrete and masonry pier foundations, 
and 
ground anchors. The ground anchor foundations are based on results from a 
series of first-of-its-kind saturated and dry soil anchor tests. The 
anchor 
tests were conducted with the support of the U.S. Department of Housing 
and 
Urban Development (HUD), the Manufactured Housing Institute (MHI), the 
Systems Building Research Alliance (SBRA, formerly the Manufactured 
Housing 
Research Alliance [MHRA]), and several ground anchor manufacturers. A 
detailed example showing step-by-step procedures on how to design a 
foundation for a manufactured home is also included.

This guidance is also valuable to designers of alternate foundations 
allowed 
by the HUD 24 CFR 3285 Model Manufactured Home Installation Standards, 
especially for homes located in Special Flood Hazard Areas (SFHAs) for 
which 
certain 24 CFR 3285 foundation designs are not applicable (24 CFR 
3285.303, 
Table 1, Note 4, et al.).

The foundation designs discussed in Chapter 10 and shown in Appendix H of 
this guide are but one group of acceptable foundation solutions. They 
should 
not be considered mandatory or all inclusive. Alternative foundation 
systems, 
designed to resist equivalent loads and provide equivalent performance, 
should be considered equally acceptable.

[Begin text box]
Limitations of the Guide

This manual has been prepared to assist in protecting manufactured homes 
from 
floods and other hazards. Builders, installers, architects, and engineers 
using this guide assume responsibility for the resulting designs and the 
performance during a natural hazard event.

The foundation designs and analyses presented in the guide are based on 
load 
combinations contained in the American Society of Civil Engineers (ASCE 7-
05) 
and the 2006 version of the International Residential Code® (IRC®).
[End text box]





ACKNOWLEDGMENTS

The Federal Emergency Management Agency would like to acknowledge the 
significant contributions made by the following individuals in developing 
the 
Second Edition of this publication.

John Ingargiola FEMA Building Science Branch
Edward Laatsch FEMA Building Science Branch
Marcus Barnes FEMA Building Science Branch 
Lois Forster FEMA Floodplain Management Branch
Brad LoarF EMA Region IV
Mike Mahoney FEMA Building Science Branch
Cliff Oliver FEMA Acquisition Branch 
John Plisich FEMA Region IV
Mike Robinson FEMA Floodplain Management Branch
Paul Rooney FEMA Data and Dissemination Management Section 
Juanita Thompson FEMA Floodplain Management Branch
Phil Bergeldt Florida Department of Highway Safety and Motor Vehicles, 
Mobile 
Home and Recreational Vehicle Construction
Mike Blanford HUD Office of Policy Development and Research
Jason McJury HUD Office of Manufactured Housing Programs
Rick Mendlen HUD Office of Manufactured Housing Programs
Kelly Cobeen Cobeen & Associates
Bill Coulbourne Applied Technology Council
Deb Daly Greenhorne & O’Mara
Bill Farish Clayton Homes
Jeff Inks Manufactured Housing Institute
Joseph Klein Dewberry
Emmanuel Levy Systems Building Research Alliance (formerly Manufactured 
Housing Research Alliance)
Julie Liptak Greenhorne & O’Mara
Thayer Long Manufactured Housing Institute
Dave Low DK Low and Associates
Bonnie Manley American Iron and Steel Institute
Therese McAllister National Institute of Standards and Technology
Ken Morris Oklahoma Water Resources Board
Mark Nunn Manufactured Housing Institute
George Porter Manufactured Housing Resources
Jim Rossberg American Society of Civil Engineers
Chuck Sanders Former Alabama State NFIP Coordinator
Adrienne Sheldon URS
John Squerciati Dewberry
Bill Turney Florida Manufactured Housing Association
Frank Walter Manufactured Housing Institute
Mark Weiss Manufactured Housing Association for Regulatory Reform
Jimmy Yeung Greenhorne & O’Mara
Naomi Chang Zajic Greenhorne & O’Mara
Brian Zelenko URS





TABLE OF CONTENTS

Preface i
Acknowledgments iii
1 Introduction 1-1
1.1 Purpose and Scope of the Guide 1-1
1.2 Background 1-3 
1.2.1 Manufactured Homes in the United States 1-3
1.2.2 National Flood Insurance Program 1-5
1.2.3 Performance of Manufactured Homes in Wind and Flood Events 1-6
1.2.3.1 Performance of Pre-1994 Manufactured Homes 1-6
1.2.3.2 Performance of Post-1994 Manufactured Homes 1-7
1.2.3.3 Performance of Manufactured Homes During Hurricane Charley (2004) 
in 
Florida 1-8

2 Manufactured Homes 2-1
2.1 Manufactured Home Characteristics 2-1
2.1.1 Chassis Support System 2-1
2.1.2 Integrated Support System 2-2
2.1.3 Envelope Construction 2-2
2.1.4 Double Section 2-3
2.2 Types of Foundation Systems 2-3
2.2.1 Typical Foundation Systems 2-5
2.2.1.1 Typical Installation 2-5
2.2.1.2 Piers and Ground Anchors 2-6
2.2.1.3 Perimeter Wall Foundations 2-7
2.2.2 Proprietary Systems 2-7
2.3 Utilities and Mechanical Equipment 2-8
2.3.1 Utilities Placement 2-8
2.3.2 Mechanical Access 2-9
2.4 Attachments – Carports, Decks, Porches, and Awnings 2-10

3 Regulatory Requirements 3-1
3.1 Introduction to the NFIP 3-1
3.2 Identifying and Mapping Flood Hazards 3-2
3.3 The NFIP's Community Rating System (CRS) 3-8
3.4 NFIP Definitions Related to Manufactured Homes 3-8
3.5 General NFIP Floodplain Management Requirements for Manufactured Homes 
3-
9
3.6 NFIP Requirements for Manufactured Homes in Riverine and Inland Flood 
Zones 3-10
3.6.1 Approximate A Zones 3-11
3.6.2 Elevation in A, A1-30, AE, and AH Zones 3-13
3.6.3 3-Foot Pier Foundation 3-14
3.6.4 Elevation in Zone AO 3-16
3.6.5 Anchoring 3-17
3.6.6 Flood Damage-Resistant Materials 3-18
3.6.7 Utilities and Mechanical Equipment  3-18
3.6.8 Enclosed Areas 3-19
3.6.9 Floodways 3-20
3.7 NFIP Requirements for Manufactured Homes in Coastal Flood Areas 3-22
3.7.1 Elevation and Anchoring 3-23
3.7.2 Fill 3-25
3.7.3 Enclosed Areas and Breakaway Walls 3-25
3.7.4 Setbacks 3-26
3.8 Existing Manufactured Homes in Flood Hazard Areas 3-27
3.8.1 Relocation 3-27
3.8.2 Evacuation 3-28
3.8.2.1 Manufactured Home Substantially Improved or Returned to a 
Different 
Site or Pad in an Existing Manufactured Home Park 3-29
3.8.2.2 Manufactured Home Placed in a New Manufactured Home Park or 
Subdivision 3-30
3.9 HUD Manufactured Home Construction and Safety Standards 3-30
3.10 HUD Model Manufactured Home Installation Standards 3-32
3.11 Model Building Code Requirements 3-34
3.11.1 IRC 2006 3-34
3.11.2 NFPA 5000 3-35
3.11.3 NFPA 501 3-36
3.11.4 NFPA 225 3-36

4  Site and Development Options 4-1
4.1 Step 1: Compiling Site Information 4-2
4.2 Step 2: Reviewing Basic Siting Information 4-4
4.3 Step 3: Hazard Analysis and Risk Assessment 4-4
4.3.1 Flooding 4-5
4.3.1.1 Accessibility 4-6
4.3.2 Other Hazards 4-8
4.4 Step 4: Protecting Properties In and Near Hazard-Prone Areas 4-10
4.4.1 Placement Options 4-10
4.4.1.1 Flood-Prone Areas 4-10
4.4.1.2 Areas Subject to Landslides 4-12
4.4.2 Design and Construction Techniques 4-12
4.4.2.1 Flood-Prone Areas 4-12
4.4.2.2 Dam Failure Inundation Areas 4-12
4.4.2.3 Areas Subject to Landslides 4-13
4.4.2.4 Areas Subject to Seismic Events 4-13
4.4.2.5 Areas Subject to Wind/Debris Hazards 4-13
4.5  Step 5: Deciding on Property Development: Proceed or Reject 4-13

5 Natural Hazards – Design Considerations 5-1
5.1 Flood Data 5-1
5.2 Flood Characteristics 5-5
5.2.1 Frequency, Duration, and Rate of Rise 5-5
5.2.2 Flood Elevation and Depth 5-7
5.2.3 Hydrostatic (Buoyancy) Forces 5-8
5.2.4 Hydrodynamic Forces 5-9
5.2.5 Erosion and Scour 5-12
5.2.6 Debris Impact Forces 5-13
5.3 Wind  5-14
5.3.1  Wind Forces on Structures 5-15
5.3.2 Wind Forces in Combination with Flood Forces 5-15
5.4 Earthquakes 5-16
5.4.1 Design Philosophy 5-16
5.4.2 Design Standard 5-16
5.5 Evaluation of Multi-Hazards 5-17
5.5.1 Load Combinations (ASCE 7) 5-18
5.5.1.1 Strength Design (Load and Resistance Factor Design) 5-18
5.5.1.2 Allowable Stress Design (also known as Working Stress Design) 5-19

6 Soils 6-1
6.1 Bearing Capacity 6-1
6.2 Effects of Flood Duration and Frequency on Soil 6-2
6.3 Soil Liquefaction 6-2
6.4 Recommended Soil Testing and Criteria for Manufactured Home 
Installations 
6-3

7 Ground Anchors 7-1
7.1 Types of Anchors and Installed Configurations 7-2
7.1.1 Types of Anchors 7-2
7.1.1.1 Helical Earth Anchors 7-2
7.1.1.2 Concrete Anchors 7-2
7.1.1.3 Cross Drive Anchors 7-2
7.1.2 Anchor Construction and Capacity 7-3
7.1.3 Anchor Selection	 7-3
7.1.4 Anchor Installation 7-4
7.1.5 Anchor Performance 7-5
7.1.6 Anchors and Other Foundation Elements 7-8
7.2 FEMA Anchor Test Program 7-8
7.2.1 Anchors in Saturated Soils 7-8
7.2.2 Anchor Test Results 7-9
7.3 Recommended Ground Anchor Certification, Performance, and Design 
Values 
7-11
7.3.1 Recommended Ground Anchor Certification Performance 7-11
7.3.2 Recommended Ground Anchor Design Values 7-11
7.4 Ground Anchors in Seismically Active Areas 7-13

8 Foundation Systems 8-1
8.1 Introduction 8-1
8.2 Enclosed Foundations 8-2
8.3 Open Foundations and Breakaway Walls 8-3
8.3.1 Pier Systems 8-3
8.3.1.1 Reinforced Pier Systems 8-4
8.3.1.2 Unreinforced Pier Systems 8-5
8.3.2 Pile Foundations 8-7
8.4 Bracing 8-9
8.5 Footings 8-10
8.6 Foundation Materials Selection 8-11
8.6.1 Wood Foundations -12
8.6.2 Concrete Foundations 8-12
8.6.3 Steel Foundations 8-13
8.6.4 Masonry Foundations 8-13
8.7 Foundation Selection and Flood Resistance	8-13
8.7.1 Flooding Types 8-14
8.7.2 Flood Characteristics 8-14
8.7.3 Flood Hazard Zones 8-15
8.7.4 Proximity to Flood Source 8-15
8.7.5 Foundation Selection Guidance 8-16

9 Recommended Design Process and Criteria for Manufactured Home 
Foundations in SFHAs 9-1
9.1 Performance Criteria 9-1
9.2 Design Criteria 9-1
9.3 Design Process 9-2
9.3.1 Step 1: Determine Design Criteria 9-3
9.3.2 Step 2: Select a Design Methodology and Assess Load Combinations and 
Failure Modes 9-4
9.3.2.1 Design Methodology 9-4
9.3.2.2 Load Combinations 9-4
9.3.2.3 Primary Failure Modes 9-4
9.3.3 Step 3: Select Foundation Type and Material 9-5
9.3.4 Step 4: Determine Forces at Connections and on Foundation Components 
9-6
9.3.5 Step 5: Specify Connections and Framing Methods Along with Component 
Dimensions to Satisfy Load Conditions 9-6
9.3.6 Step 6: Note All Design Assumptions and Details on Drawings 9-6

10 Recommended Foundations 10-1
10.1 Design Criteria for Recommended Foundations 10-1
10.1.1 Reinforced Masonry Perimeter Foundation Walls 10-2
10.1.2 Wood Framed Perimeter Foundation Walls 10-3
10.1.3 Braced Masonry Pier Designs 10-3
10.1.4 Wood H-Frame Designs 10-4
10.1.5 Ground Anchor Designs 10-4
10.2 Summary of Recommended Foundations 10-5
10.3 Floodwater Velocity Design Considerations for Pier Foundations 10-6
10.4 Recommended Foundation Designs for Seismic Areas 10-7
10.4.1 Concrete Masonry Pier Foundation Designs 10-7
10.4.2 Masonry Wall Foundation Designs 10-7
10.4.3 Wood Framed Foundation Designs 10-8
10.5 Design Drawings 10-8

Appendices
Appendix A: References 
Appendix B: Sources for Flood Information 
Appendix C: Flood Velocity Determination
Appendix D: Definitions 
Appendix E: Acronyms and Abbreviations 
Appendix F: Example Calculations
Appendix G: Wind Zone Comparisons (HUD's MHCSS and ASCE 7-05)
Appendix H: Pre-Engineered and Prescriptive Foundation Designs

Figures
Chapter 1
Figure 1-1. Basic wind zone map for manufactured housing 1-4
Figure 1-2. Inadequate turnbuckle anchor installed by the homeowner on 
this 
pre-1994 manufactured home, coupled with lack of elevation and an 
unreinforced foundation system, led to severe damage. 1-7
Figure 1-3. The addition to this manufactured home was destroyed, causing 
considerable damage to the rest of the home. 1-7
Figure 1-4. Reinforced masonry pier foundation system under a manufactured 
home installed after 1994 that performed well. 1-8
Figure 1-5. Manufactured home in Cudjoe Key, Florida, built and installed 
after 1994, survived Hurricane Georges with only minor damage caused by 
the loss of an awning. 1-8

Chapter 2
Figure 2-1. Traditional chassis system. 2-2
Figure 2-2. Integrated floor system consisting of steel-reinforced 
perimeter framing. 2-2
Figure 2-3. Main construction features of a typical manufactured home. 2-4
Figure 2-4. One section of a double-section manufactured home being 
transported. 2-5
Figure 2-5. Typical installation of a manufactured home on masonry block 
piers with tie-down straps. 2-6
Figure 2-6. Typical installation of a double-section manufactured home on 
a 
pier and ground anchor foundation system. 2-6
Figure 2-7. Perimeter wall foundation under a manufactured home. 2-7
Figure 2-8. Utility line damage in unstable soils.	2-9

Chapter 3
Figure 3-1. Sample DFIRM. 3-4
Figure 3-2(a). Sample FIS Summary of Discharges table. 3-5
Figure 3-2(b). Sample FIS Floodway Data. 3-5
Figure 3-2(c). Sample FIS Flood Profile. 3-6
Figure 3-3.	Manufactured home with lowest floor elevated to the BFE. 3-
14
Figure 3-4.	Manufactured home on reinforced pier foundation 36 inches 
high. 
3-16
Figure 3-5.	DFIRM showing the floodway (cross-hatched area in Zone AE). 
3-21
Figure 3-6.	Manufactured home with the bottom of the lowest horizontal 
structural member elevated to the BFE. 3-24
Figure 3-7.	Mean high tide line development restriction. 3-27
Figure 3-8 Coastal development well-suited to the land: generous setbacks, 
in 
combination with deep lots and avoidance of dune areas, should afford 
protection from erosion and flooding for years to come. 3-27
Figure 3-9. Certification plate for manufactured homes built after June 
15, 
1976. 3-31

Chapter 4
Figure 4-1. Portions of an FIS and a FIRM. 4-7
Figure 4-2. Floodplain/floodway schematic. 4-11

Chapter 5
Figure 5-1. Example of a FIRM. 5-2
Figure 5-2. FIS Summary of Discharges table. 5-3
Figure 5-3. FIS Stream Flood Profile. 5-4
Figure 5-4. FIS Floodway Data table. 5-4
Figure 5-5. Buoyancy forces acting on a structure. 5-9
Figure 5-6. Failure due to sliding. 5-10
Figure 5-7. manufactured home destroyed by the hydrodynamic forces of 
flooding. 5-10
Figure 5-8. Failure of a modular home due to high winds. The home lifted 
off 
of its foundation (concrete slab) when the connections failed. 5-14
Figure 5-9. A manufactured home that failed during a high-wind event. 5-15

Chapter 7
Figure 7-1. Cross drive anchor. 7-2
Figure 7-2. Single and double helix ground anchors with strap connection 
and 
single helix anchor with a closed-eye connection. 7-3
Figure 7-3. Electric anchor drive machine. 7-4
Figure 7-4. Typical ground anchor installation. 7-5
Figure 7-5. In line ground anchor installation. 7-6
Figure 7-6. Typical response for an axially loaded anchor. 7-7
Figure 7-7. Typical response for a non-axially loaded anchor used with a 
stabilizer plate. 7-8
Figure 7-8. Failed foundation system that used masonry piers. 7-9
Figure 7-9. Three graphics showing the anchor configurations described in 
Tables 7-2 and 7-3.  7-11

Chapter 8
Figure 8-1. A manufactured home elevated on a perimeter foundation wall. 
8-2
Figure 8-2. Reinforced masonry and concrete piers. 8-5
Figure 8-3. Bolted connection between frame and reinforced pier. 8-6
Figure 8-4. Manufactured home on a pile foundation. 8-7
Figure 8-5. Pile driving methods. 8-8
Figure 8-6. Diagonal bracing. 8-10
Figure 8-7. Knee bracing. 8-10

Chapter 9
Figure 9-1. A home that was partially submerged and displaced from its 
foundation by hydrostatic forces. 9-5

Tables

Chapter 3
Table 3-1. Common SFHA Designations for Riverine or Inland Flood Zones 3-6
Table 3-2. Common SFHA Designations for Coastal Flood Areas 3-6

Chapter 4
Table 4-1. Information Checklist 4-2
Table 4-2. Partial Listing of Local, Regional, and State Responsibilities 
4-4
Table 4-3. Flood Hazards 4-5
Table 4-4. Hazard-Prone Areas 4-9

Chapter 5
Table 5-1. Sources for Information About Past Flood Events 5-6
Table 5-2. Load Combination Nomenclature (ASCE 7) 5-17

Chapter 7
Table 7-1. Soil Classifications Using a Standard Torque Probe (STP) 7-4
Table 7-2. Dry Site Anchor Data 7-10
Table 7-3. Wet Site Anchor Data 7-10
Table 7-4. Recommended Design Loads – from FEMA Ground Anchor Testing 
Program 
7-12
Table 7-5. Recommended Design Stiffness for Tested Anchors 7-12

Chapter 8
Table 8-1. Recommended Manufactured Home Foundation Selection for 
Lake/Pond 
Flooding (for very low velocity less than 1 fps) 8-16
Table 8-2. Recommended Manufactured Home Foundation Selection for Riverine 
Flood Zones (and maximum flood flow velocity) 8-17
Table 8-3. Recommended Manufactured Home Foundation Selection for Coastal 
Flood Zones 8-18

Chapter 9
Table 9-1. Design Standards and Publishers for Building Materials 9-6
Chapter 10
Table 10-1. Summary of Recommended Foundations 10-5
Table 10-2. Design Flood Flow Velocity for Concrete Masonry Unit 
Foundations 
10-6
Table 10-3. Foundation Drawings 10-8