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Mobile home crawl space (C) Daniel FriedmanManufactured Home & Mobile Home Tie-Downs
Tie-Down Specifications & HUD Wind Zone Maps, Wind Design Pressures, Roof Live Load Specifications

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Mobile home stabilizing systems & tie down requirements for doublewides, mobile homes, multiwides, & trailer.

Here we describe defects commonly found in the stabilizing systems, cables, & tie downs for wind & storm damage resistance of mobile homes, doublewides, multiwides, trailers, risking lack of resistance to wind or storm damage.

We include HUD Specifications for wind zone data, design loads, roof loads & tie-down specifications to protect manufactured homes and mobile homes or trailers in high wind areas.



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STABILIZING SYSTEMS - Tie Downs & Stabilizing Systems for Mobile Homes

Mobile home still on wheels (C) Daniel Friedman

Our photo shows that although this trailer has been placed on a concrete slab foundation, it still rests on its wheels and on temporary jack stands. No piers, no tie-downs, no permanent support was provided.

Definitions of Tie-Downs or Stabilizing Systems for Manufactured / Mobile HOmes

After the very extensive damage and flooding caused by Hurricane Irma in Florida in 2017, the New York Times reported that a number of Florida mobile homes had survived the Category 4 hurricane, most-likely due to both the rapid decline in the storm's strength as it moved across the state but also due to "... toughened construction and installation regulations for mobile homes ...". - Treaster, Joseph B., Henry Fountain, "Stricter Regulations, and Depleted Storm, May Have Helped Save Mobile Homes", The New York Times, 15 September 2017 p. A14.

The Times reporters noted that increased building standards put in place in Florida after Hurricane Andrew (August 1992) and mobile homes built to those new standards meant that homes had a significantly-improved survival rate. While carports and awnings blew to smithereens and some building siding and roof shingles were lost, fewer homes in Key Largo Florida, about ten percent, suffered significant roof damage. (Those homes suffered significant water damage too.)

It appears likely that the requirement for multiple anchor cables including over-roof cabling added after Hurricane Andrew protected many mobile or manufactured homes in the area.

Inspection Points for Mobile Home Anchoring Systems

Mobile home on blocks (C) Daniel Friedman

Tie downs for mobile homes, trailers, double-wides are usually expected to be placed and connected according to details provided in the mobile home installation manual (have you ever seen one?). If you know your mobile home or trailer model name and perhaps serial number, you may be able to contact the mobile home manufacturer to ask for an installation manual.

Watch out: HUD-7584 prohibits dependence on screw-in type tie-down anchors commonly used in manufactured home anchorage systems.

Links to more detailed mobile home or trailer tie-down installation specifications, methods, and advice can be found at Structural Advice.

HUD Codes on Manufactured & Mobile Home Tiedown Systems for Wind & Earthquake Damage Protection

MANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDS, Part 3280 contains 10 subparts pertaining to General (data plate and certification contents and locations), Plans (dimensions, exits, etc), Fire Safety, Body and Frame, Testing, Thermal Protection, Heating/Cooling and venting systems, Electrical, and Transportation (axles, springs, drawbar).

Excerpts below describe wind zone specifications & requirements for manufactured homes.

HUD Wind Zone Map for Manufactured Housing

[Click to enlarge any image]

HUD Wind Zone Data Map

Part 3282 (the document link just above) discusses preemption of state laws, among other things, and requires a new unit to be delivered with a "consumer manual" containing required information about the unit. Thanks to NHFireBear for this update, April 2015. Retrieved 9 April 2015, original source: www.gpo.gov/fdsys/pkg/CFR-2001-title24-vol5/pdf/CFR-2001-title24-vol5-subtitleB.pdf [note this is a very large PDF that contains other sections. Our live link above has excerpted the Manufactured Home standards section from the HUD document Ed.]

Excerpting from the above:

§3280.305 Structural design requirements [for Manufactured Housing]

(a) General.

Each manufactured home shall be designed and constructed as a completely integrated structure capable of sustaining the design load requirements of this standard, and shall be capable of transmitting these loads to stabilizing devices without exceeding the allowable stresses or deflections.

Roof framing shall be securely fastened to wall framing, walls to floor structure, and floor structure to chassis to secure and maintain continuity between the floor and chassis, so as to resist wind overturning, uplift, and sliding as imposed by design loads in this part.

Uncompressed finished flooring greater than 1/8 inch in thickness shall not extend beneath load-bearing walls that are fastened to the floor structure.

(b) Design loads

(1) Design dead loads. Design dead loads shall be the actual dead load supported by the structural assembly under consideration.

(2) Design live loads. The design live loads and wind and snow loads shall be as specified in this section and shall be considered to be uniformly distributed. The roof live load or snow load shall not be considered as acting simultaneously with the wind load and the roof live or snow load and floor live loads shall not be considered as resisting the overturning moment due to wind.

(3) When engineering calculations are performed, allowable unit stresses may be increased as provided in the documents referenced in §3280.304 except as otherwise indicated in §§3280.304(b)(1) and 3280.306(a).

(4) Whenever the roof slope does not exceed 20 degrees, the design horizontal wind loads required by §3280.305(c)(1) may be determined without including the vertical roof projection of the manufactured home. However, regardless of the roof slope of the manufactured home, the vertical roof projection shall be included when determining the wind loading for split level or clerestory type roof systems.

(c) Wind, snow, and roof loads—(1) Wind loads—design requirements.

(i) Standard wind loads (Zone I).

When a manufactured home is not designed to resist the wind loads for high wind areas (Zone II or Zone III) specified in paragraph (c)(1)(ii) of this section, the manufactured home and each of its wind resisting parts and portions shall be designed for horizontal wind loads of not less than 15 psf and net uplift load of not less than 9 psf.

(ii) Wind loads for high wind areas (Zone II and Zone III).

When designed for high wind areas (Zone II and Zone III), the manufactured home, each of its wind resisting parts (including, but not limited to, shear walls, diaphragms, ridge beams, and their fastening and anchoring systems), and its components and cladding materials (including, but not limited to, roof trusses, wall studs, exterior sheathing, roofing and siding materials, exterior glazing, and their connections and fasteners) shall be designed by a Professional Engineer or Architect to resist:

(A) The design wind loads for Exposure C specified in ANSI/ASCE 7–88, ‘‘Minimum Design Loads for Buildings and Other Structures,’’ for a fifty-year recurrence interval, and a design wind speed of 100 mph, as specified for Wind Zone II, or 110 mph, as specified for Wind Zone III (Basic Wind Zone Map); or

(B) The wind pressures specified in the following table:

HUD Table of Design Wind Pressures for Manufactured Housing § 3280.305

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HUD Wind Zone Data Table from 3280.305: Design wind pressures for manufactured Housing

(2) Wind loads—zone designations.

The Wind Zone and specific wind design load requirements are determined by the fastest basic wind speed (mph) within each Zone and the intended location, based on the Basic Wind Zone Map, as follows:

(i) Wind Zone I.

Wind Zone I consists of those areas on the Basic Wind Zone Map that are not identified in paragraphs (c)(2)(ii) or (iii) of this section as being within Wind Zone II or III, respectively.

(ii) Wind Zone II.....100 mph.

The following areas are deemed to be within Wind Zone II of the Basic Wind Zone Map:
Local governments: The following local governments listed by State (counties, unless specified otherwise):

Alabama: Baldwin and Mobile.

Florida: All counties except those identified in paragraph (c)(1)(i)(C) of this section as within Wind Zone III.

Georgia: Bryan, Camden, Chatham, Glynn, Liberty, McIntosh.

Louisiana: Parishes of Acadia, Allen, Ascension, Assumption, Calcasieu, Cameron, East Baton Rouge, East Feliciana, Evangeline, Iberia, Iberville, Jefferson Davis, LaFayette, Livingston, Pointe Coupee, St. Helena, St. James, St. John the Baptist, St. Landry, St. Martin, St. Tammany, Tangipahoa, Vermillion, Washington, West Baton Rouge, and West Feliciana.

Maine: Hancock and Washington.

Massachusetts: Barnstable, Bristol, Dukes, Nantucket, and Plymouth.

Mississippi: George, Hancock, Harrison, Jackson, Pearl River, and Stone. North Carolina: Beaufort, Brunswick, Camden, Chowan, Columbus, Craven, Currituck, Jones, New Hanover, Onslow, Pamlico, Pasquotank, Pender, Perquimans, Tyrrell, and Washington. South Carolina: Beaufort, Berkeley, Charleston, Colleton, Dorchester, Georgetown, Horry, Jasper, and Williamsburg.

Texas: Aransas, Brazoria, Calhoun, Cameron, Chambers, Galveston, Jefferson, Kenedy, Kleberg, Matagorda, Nueces, Orange, Refugio, San Patricio, and Willacy.

Virginia: Cities of Chesapeake, Norfolk, Portsmouth, Princess Anne, and Virginia Beach.

(iii) Wind Zone III.....110 mph

The following areas are considered to be within Wind Zone III of the Basic Wind Zone Map:

(A) States and Territories: The entire State of Hawaii, the coastal regions of Alaska (as determined by the 90 mph isotach on the ANSI/ASCE 7–88 map), and all of the U.S. Territories of American Samoa, Guam, Northern Mariana Islands, Puerto Rico, Trust Territory of the Pacific Islands, and the United States Virgin Islands.

(B) Local governments: The following local governments listed by State (counties, unless specified otherwise):

Florida: Broward, Charlotte, Collier, Dade, Franklin, Gulf, Hendry, Lee, Martin, Manatee, Monroe, Palm Beach, Pinellas, and Sarasota.

Louisiana: Parishes of Jefferson, La Fourche, Orleans, Plaquemines, St. Bernard, St. Charles, St. Mary, and Terrabonne.

North Carolina: Carteret, Dare, and Hyde.

(iv) Consideration of local requirements. For areas where local building code requirements exceed the design wind speed requirements of these standards,
§ 3280.305 the Department will consider the adoption through rulemaking of the more stringent requirements of the State or local building authority.

Manufactured & Mobile Home Wind Protection Standards & Codes

Full details are at PART 3280—MANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDS [PDF] newer copy retrieved 2017/07/13 - faster-loading

Excerpt:

§3280.306 Windstorm protection.

(a) Provisions for support and anchoring systems.

Each manufactured home shall have provisions for support/anchoring or foundation systems that, when properly designed and installed, will resist overturning and lateral movement (sliding) of the manufactured home as imposed by the respective design loads.

For Wind Zone I, the design wind loads to be used for calculating resistance to overturning and lateral movement shall be the simultaneous application of the wind loads indicated in §3280.305(c)(1)(i), increased by a factor of 1.5. The 1.5 factor of safety for Wind Zone I is also to be applied simultaneously to both the vertical building projection, as horizontal wind load, and across the surface of the full roof structure, as uplift loading.

For Wind Zones II and III, the resistance shall be determined by the simultaneous application of the horizontal drag and uplift wind loads, in accordance with §3280.305(c)(1)(ii).

The basic allowable stresses of materials required to resist overturning and lateral movement shall not be increased in the design and proportioning of these members. No additional shape or location factors need to be applied in the design of the tiedown system. The dead load of the structure may be used to resist these wind loading effects in all Wind Zones.

(1) The provisions of this section shall be followed and the support and anchoring systems shall be designed by a Registered Professional Engineer or Architect.

(2) The manufacturer of each manufactured home is required to make provision for the support and anchoring systems but is not required to provide the anchoring equipment or stabilizing devices. When the manufacturer's installation instructions provide for the main frame structure to be used as the points for connection of diagonal ties, no specific connecting devices need be provided on the main frame structure.

(b) Contents of instructions.

(1) The manufacturer must provide printed instructions with each manufactured home that specify the location and required capacity of stabilizing devices on which the home's design is based.

The manufacturer must identify by paint, label, decal stencil, or other means: the location of each column support pier location required along the marriage line(s) of multi­section manufactured homes; each pier location required along the perimeter of the home; each required shear wall pier support; and any other special pier support locations specified in the manufacturer's printed instructions. Such identifications must be visible after the home is installed.

The manufacturer must provide drawings and specifications, certified by a registered professional engineer or architect, that indicate at least one acceptable system of anchoring, including the details or required straps or cables, their end connections, and all other devices needed to transfer the wind loads from the manufactured home to an anchoring or foundation system.

(2) For anchoring systems, the instructions shall indicate:

(i) The minimum anchor capacity required;

(ii) That anchors should be certified by a professional engineer, architect, or a nationally recognized testing laboratory as to their resistance, based on the maximum angle of diagonal tie and/or vertical tie loading (see paragraph (c)(3) of this section) and angle of anchor installation, and type of soil in which the anchor is to be installed;

(iii) That ground anchors are to be embedded below the frost line, unless the foundation system is frost­protected in accordance with §§3285.312(b) and 3285.404 of the Model Manufactured Home Installation Standards in this chapter.

(iv) That ground anchors must be installed to their full depth, and stabilizer plates must be installed in accordance with the ground anchor listing or certification to provide required resistance to overturning and sliding.

(v) That anchoring equipment should be certified by a registered professional engineer or architect to resist these specified forces in accordance with testing procedures in ASTM D3953­97, Standard Specification for Strapping, Flat Steel and Seals (incorporated by reference, see §3280.4).

(c) Design criteria. The provisions made for anchoring systems shall be based on the following design criteria for manufactured homes.

(1) The minimum number of ties provided per side of each home shall resist design wind loads required in §3280.305(c)(1).

(2) Ties shall be as evenly spaced as practicable along the length of the manufactured home, with not more than two (2) feet open­end spacing on each end.

(3) Vertical ties or straps shall be positioned at studs. Where a vertical tie and a diagonal tie are located at the same place, both ties may be connected to a single anchor, provided that the anchor used is capable of carrying both loadings, simultaneously.

(4) Add­on sections of expandable manufactured homes shall have provisions for vertical ties at the exposed ends.

(d) Requirements for ties. Manufactured homes in Wind Zone I require only diagonal ties. These ties shall be placed along the main frame and below the outer side walls. All manufactured homes designed to be located in Wind Zones II and III shall have a vertical tie installed at each diagonal tie location.

(e) Protection requirements. Protection shall be provided at sharp corners where the anchoring system requires the use of external straps or cables. Protection shall also be provided to minimize damage to siding by the cable or strap.

(f) Anchoring equipment—load resistance. Anchoring equipment shall be capable of resisting an allowable working load equal to or exceeding 3,150 pounds and shall be capable of withstanding a 50 percent overload (4,725 pounds total) without failure of either the anchoring equipment or the attachment point on the manufactured home.

(g) Anchoring equipment—weatherization. Anchoring equipment exposed to weathering shall have a resistance to weather deterioration at least equivalent to that provided by a coating of zinc on steel of not less than 0.30 ounces per square foot of surface coated, and in accordance with the following:

(1) Slit or cut edges of zinc­coated steel strapping do not need to be zinc coated.

(2) Type 1, Finish B, Grade 1 steel strapping, 1 1 ∕4 inches wide and 0.035 inches in thickness, certified by a registered professional engineer or architect as conforming with ASTM D3953­97, Standard Specification for Strapping, Flat Steel and Seals (incorporated by reference, see §3280.4).

§3280.307 Resistance to elements and use.

(a) Exterior coverings shall be of moisture and weather resistive materials attached with corrosion resistant fasteners to resist wind, snow and rain. Metal coverings and exposed metal structural members shall be of corrosion resistant materials or shall be protected to resist corrosion. All joints between portions of the exterior covering shall be designed, and assembled to protect against the infiltration of air and water, except for any designed ventilation of wall or roof cavity.

(b) Joints between dissimilar materials and joints between exterior coverings and frames of openings shall be protected with a compatible sealant suitable to resist infiltration of air or water.

(c) Where adjoining materials or assemblies of materials are of such nature that separation can occur due to expansion, contraction, wind loads or other loads induced by erection or transportation, sealants shall be of a type that maintains protection against infiltration or penetration by air, moisture or vermin.

(d) Exterior surfaces shall be sealed to resist the entrance of rodents

Additional Structural Requirements & Specifications for Manufactured Homes

See MOBILE HOME STRUCTURAL DEFECTS

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