[Title 24 CFR 3280.305]
[Code of Federal Regulations (annual edition) - May 1, 2001 Edition]
[Title 24 - HOUSING AND URBAN DEVELOPMENT]
[Subtitle B - Regulations Relating to Housing and Urban Development]
[Chapter Xx - OFFICE OF ASSISTANT SECRETARY FOR HOUSING--FEDERAL HOUSING]
[Part 3280 - MANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDS]
[Subpart D - Body and Frame Construction Requirements]
[Sec. 3280.305 - Structural design requirements.]
[From the U.S. Government Printing Office]


24HOUSING AND URBAN DEVELOPMENT52001-05-012001-05-01falseStructural design requirements.3280.305Sec. 3280.305HOUSING AND URBAN DEVELOPMENTRegulations Relating to Housing and Urban DevelopmentOFFICE OF ASSISTANT SECRETARY FOR HOUSING--FEDERAL HOUSINGMANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDSBody and Frame Construction Requirements
Sec. 3280.305  Structural design requirements.

    (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 
Sec. 3280.304 except as otherwise indicated in Secs. 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 Sec. 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:

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    (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:

                     Table of Design Wind Pressures
------------------------------------------------------------------------
                                           Wind zone II    Wind zone III
                 Element                    design wind     design wind
                                           speed 100 MPH   speed 110 MPH
------------------------------------------------------------------------
Anchorage for lateral and vertical
 stability (See Sec.  3280.306(a)):
    Net Horizontal Drag1,2...  \3\ 39  47
     Fastening and Anchorage Systems 1,2             PSF             PSF
    Ridge beams and other Main Roof              -30 PSF         -36 PSF
     Support Beams (Beams supporting
     expanding room sections, etc.).....
Components and cladding:
    Roof trusses \4\ in all areas;           \5\ -39 PSF     \5\ -47 PSF
     trusses shall be doubled within 3'-
     0'' from each end of the roof......
    Exterior roof coverings, sheathing       \5\ -39 PSF     \5\ -47 PSF
     and fastenings \4\,\6\,\7\ in all
     areas except the following.........
        Within 3'-0'' from each gable        \5\ -73 PSF     \5\ -89 PSF
         end (overhang at end wall) of
         the roof or endwall if no
         overhang is provided
         \4\,\6\,\7\....................
        Within 3'-0'' from the ridge and     \5\ -51 PSF     \5\ -62 PSF
         eave (overhang at sidewall) or
         sidewall if no eave is provided
         \4\,\6\,\7\....................
    Eaves (Overhangs at Sidewalls)           \5\ -51 PSF     \5\ -62 PSF
     \4\,\6\,\7\........................
    Gables (Overhangs at Endwalls)           \5\ -73 PSF     \5\ -89 PSF
     \4\,\6\,\7\........................
Wall studs in sidewalls and endwalls,
 exterior windows and sliding glass
 doors (glazing and framing), exterior
 coverings, sheathing and fastenings
 \8\:
        Within 3'-0'' from each corner    48  58
         of the sidewall and endwall....             PSF             PSF
        All other areas.................  38  46
                                                     PSF            PSF
------------------------------------------------------------------------
NOTES:
 
1 The net horizontal drag of 39 PSF to be used in
  calculating Anchorage for Lateral and Vertical Stability and for the
  design of Main Wind Force Resisting Systems is based on a distribution
  of wind pressures of +0.8 or +24 PSF to the windward wall and -0.5 or
  15 PSF to the leeward wall.
2 Horizontal drag pressures need not be applied to roof projections when
  the roof slope does not exceed 20 degrees.
3 + sign would mean pressures are acting towards or on the structure; -
  sign means pressures are acting away from the structure; 
  sign means forces can act in either direction, towards or away from
  the structure.
4 Design values in this ``Table'' are only applicable to roof slopes
  between 10 degrees (nominal 2/12 slope) and 30 degrees.
5 The design uplift pressures are the same whether they are applied
  normal to the surface of the roof or to the horizontal projection of
  the roof.
6 Shingle roof coverings that are secured with 6 fasteners per shingle
  through an underlayment which is cemented to a 3/8'' structural rated
  roof sheathing need not be evaluated for these design wind pressures.
7 Structural rated roof sheathing that is at least 3/8'' in thickness,
  installed with the long dimension perpendicular to roof framing
  supports, and secured with fasteners at 4'' on center within 3'-0'' of
  each gable end or endwall if no overhang is provided and 6'' on center
  in all other areas, need not be evaluated for these design wind
  pressures.
8 Exterior coverings that are secured at 6'' o.c. to a 3/8'' structural
  rated sheathing that is fastened to wall framing members at 6'' on
  center need not be evaluated for these design wind pressures.

    (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,

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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, the Department will consider the adoption through 
rulemaking of the more stringent requirements of the State or local 
building authority.
    (3) Snow and roof loads. (i) Flat, curved and pitched roofs shall be 
designed to resist the following live loads, applied downward on the 
horizontal projection as appropriate for the design zone marked on the 
manufactured home:

------------------------------------------------------------------------
                                                                 Pounds
                                                                   per
            Zone (see Map in Sec.  3280.305(c)(4))               square
                                                                  foot
------------------------------------------------------------------------
North Zone....................................................        40
Middle Zone...................................................        30
South Zone....................................................        20
------------------------------------------------------------------------

    (ii) For exposures in areas (mountainous or other) where snow or 
wind records or experience indicate significant differences from the 
loads stated above, the Department may establish more stringent 
requirements for homes known to be destined for such areas. For snow 
loads, such requirements are to be based on a roof snow load of 0.6 of 
the ground snow load for areas exposed to wind and a roof snow load of 
0.8 of the ground snow load for sheltered areas.
    (iii) Eaves and cornices shall be designed for a net uplift pressure 
of 2.5 times the design uplift wind pressure cited in 
Sec. 3280.305(c)(1)(i) for Wind Zone I, and for the design pressures 
cited in Sec. 3280.305(c)(1)(ii) for Wind Zones II and III.
    (4) Data plate requirements. The Data Plate posted in the 
manufactured home (see Sec. 3280.5) shall designate the wind and roof 
load zones or, if designed for higher loads, the actual design external 
snow and wind loads for which the home has been designed. The Data Plate 
shall include reproductions of the Load Zone Maps shown in this 
paragraph (c)(4), with any related information. The Load Zone Maps shall 
be not less than either 3\1/2\ in. by 2\1/4\ in., or one-half the size 
illustrated in the Code of Federal Regulations.

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[GRAPHIC] [TIFF OMITTED] TR14JA94.000


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[GRAPHIC] [TIFF OMITTED] TR20OC97.004


    (d) Design load deflection. (1) When a structural assembly is 
subjected to total design live loads, the deflection for structural 
framing members shall not exceed the following (where L equals the clear 
span between supports or two times the length of a cantilever):


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Floor--L/240
Roof and ceiling--L/180
Headers, beams, and girders (vertical load)--L/180
Walls and partitions--L/180
    (2) The allowable eave or cornice deflection for uplift is to be 
measured at the design uplift load of 9 psf for Wind Zone I, and at the 
design uplift pressure cited in paragraph (c)(1)(ii) of this section for 
Wind Zones II and III. The allowable deflection shall be (2 x Lc)/180, 
where Lc is the measured horizontal eave projection from the wall.
    (e) Fastening of structural systems. (1) 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 
specified in this part.
    (2) For Wind Zones II and III, roof trusses shall be secured to 
exterior wall framing members (studs), and exterior wall framing members 
(studs) shall be secured to floor framing members, with 26 gage minimum 
steel strapping or brackets or by a combination of 26 gage minimum steel 
strapping or brackets and structural rated wall sheathing that overlaps 
the roof and floor. Steel strapping or brackets shall be installed at a 
maximum spacing of 24" on center in Wind Zone II and at a maximum of 16" 
on center in Wind Zone III. The number and type of fasteners used to 
secure the steel straps or brackets or structural sheathing shall be 
capable of transferring all uplift forces between elements being joined.
    (f) Walls. The walls shall be of sufficient strength to withstand 
the load requirements as defined in Sec. 3280.305(c) of this part, 
without exceeding the deflections as specified in Sec. 3280.305(d). The 
connections between the bearing walls, floor, and roof framework members 
shall be fabricated in such a manner as to provide support for the 
material used to enclose the manufactured home and to provide for 
transfer of all lateral and vertical loads to the floor and chassis.
    (1) Except where substantiated by engineering analysis or tests, 
studs shall not be notched or drilled in the middle one-third of their 
length.
    (2) Interior walls and partitions shall be constructed with 
structural capacity adequate for the intended purpose and shall be 
capable of resisting a horizontal load of not less than five pounds per 
square foot. An allowable stress increase of 1.33 times the permitted 
published design values may be used in the design of wood framed 
interior partitions. Finish of walls and partitions shall be securely 
fastened to wall framing.
    (g) Floors. (1) Floor assemblies shall be designed in accordance 
with accepted engineering practice standards to support a minimum 
uniform live load of 40 lb/ft \2\ plus the dead load of the materials. 
In addition (but not simultaneously), floors shall be able to support a 
200-pound concentrated load on a one-inch diameter disc at the most 
critical location with a maximum deflection not to exceed one-eighth 
inch relative to floor framing. Perimeter wood joists of more than six 
inches depth shall be stabilized against overturning from superimposed 
loads as follows: at ends by solid blocking not less than two-inch 
thickness by full depth of joist, or by connecting to a continuous 
header not less than two-inch thickness and not less than the depth of 
the joist with connecting devices; at eight-feet maximum intermediate 
spacing by solid blocking or by wood cross-bridging of not less than one 
inch by three inches, metal cross-bridging of equal strength, or by 
other approved methods.
    (2) Wood, wood fiber or plywood floors or subfloors in kitchens, 
bathrooms (including toilet compartments), laundry areas, water heater 
compartments, and any other areas subject to excessive moisture shall be 
moisture resistant or shall be made moisture resistant by sealing or by 
an overlay of nonabsorbent material applied with water-resistant 
adhesive. Use of one of the following methods would meet this 
requirement:
    (i) Sealing the floor with a water-resistant sealer; or
    (ii) Installing an overlay of a non-absorbent floor covering 
material applied with water-resistant adhesive; or
    (iii) Direct application of a water-resistant sealer to the exposed 
wood floor

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area when covered with a non-absorbent overlay; or
    (iv) The use of a non-absorbent floor covering which may be 
installed without a continuous application of a water-resistant adhesive 
or sealant when the floor covering meets the following criteria:
    (A) The covering is a continuous membrane with any seams or patches 
seam bonded or welded to preserve the continuity of the floor covering; 
and
    (B) The floor is protected at all penetrations in these areas by 
sealing with a compatible water-resistant adhesive or sealant to prevent 
moisture from migrating under the nonabsorbent floor covering; and
    (C) The covering is fastened around the perimeter of the subfloor in 
accordance with the floor covering manufacturer's instructions; and,
    (D) The covering is designed to be installed to prevent moisture 
penetration without the use of a water-resistant adhesive or sealer 
except as required in this paragraph (g). The vertical edges of 
penetrations for plumbing shall be covered with a moisture-resistant 
adhesive or sealant. The vertical penetrations located under the bottom 
plates of perimeter walls of rooms, areas, or compartments are not 
required to be sealed; this does not include walls or partitions within 
the rooms or areas.
    (3) Carpet or carpet pads shall not be installed under concealed 
spaces subject to excessive moisture, such as plumbing fixture spaces, 
floor areas under installed laundry equipment. Carpet may be installed 
in laundry space provided:
    (i) The appliances are not provided;
    (ii) The conditions of paragraph (g)(2) of this section are 
followed; and
    (iii) Instructions are provided to remove carpet when appliances are 
installed.
    (4) Except where substantiated by engineering analysis or tests:
    (i) Notches on the ends of joists shall not exceed one-fourth the 
joist depth.
    (ii) Holes bored in joists shall not be within 2 inches of the top 
or bottom of the joist, and the diameter of any such hole shall not 
exceed one-third the depth of the joist.
    (iii) Notches in the top or bottom of the joists shall not exceed 
one-sixth the depth and shall not be located in the middle third of the 
span.
    (5) Bottom board material (with or without patches) shall meet or 
exceed the level of 48 inch-pounds of puncture resistance as tested by 
the Beach Puncture Test in accordance with Standard Test Methods for 
Puncture and Stiffness of Paperboard, and Corrugated and Solid 
Fiberboard, ASTM D-781-1968 (73). The material shall be suitable for 
patches and the patch life shall be equivalent to the material life. 
Patch installation instruction shall be included in the manufactured 
home manufacturer's instructions.
    (h) Roofs. (1) Roofs shall be of sufficient strength to withstand 
the load requirements as defined in Sec. 3280.305 (b) and (c) without 
exceeding the deflections specified in Sec. 3280.305(d). The connections 
between roof framework members and bearing walls shall be fabricated in 
such a manner to provide for the transfer of design vertical and 
horizontal loads to the bearing walls and to resist uplift forces.
    (2) Roofing membranes shall be of sufficient rigidity to prevent 
deflection which would permit ponding of water or separation of seams 
due to wind, snow, ice, erection or transportation forces.
    (3) Cutting of roof framework members for passage of electrical, 
plumbing or mechanical systems shall not be allowed except where 
substantiated by engineering analysis.
    (4) All roof penetrations for electrical, plumbing or mechanical 
systems shall be properly flashed and sealed. In addition, where a metal 
roof membrane is penetrated, a wood backer shall be installed. The 
backer plate shall be not less than \5/16\ inch plywood, with exterior 
glues, secured to the roof framing system beneath the metal roof, and 
shall be of a size to assure that all screws securing the flashing are 
held by the backer plate.
    (i) Frame construction. The frame shall be capable of transmitting 
all design loads to stabilizing devices without exceeding the allowable 
load and deflections of this section. The frame shall also be capable of 
withstanding the effects of transportation shock and vibration without 
degradation as required by subpart J.

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    (1) Welded connections. (i) All welds shall be made in accordance 
with the applicable provisions of the Specification for Structural Steel 
Buildings, Allowable Stress Design and Plastic Design, AISC, June 1, 
1989. The Specification for the Design of Cold-Formed Steel Structural 
Members, AISI-1986 with 1989 addendum, and the Stainless Steel Cold-
Formed Structural Design Manual, AISI-1974.
    (ii) Regardless of the provisions of any reference standard 
contained in this subpart, deposits of weld slag or flux shall be 
required to be removed only from welded joints at the following 
locations:
    (A) Drawbar and coupling mechanisms;
    (B) Main member splices, and
    (C) Spring hanger to main member connections.
    (2) Protection of metal frames against corrosion. Metal frames shall 
be made corrosion resistant or protected against corrosion. Metal frames 
may be protected against corrosion by painting.

[40 FR 58752, Dec. 18, 1975. Redesignated at 44 FR 20679, Apr. 6, 1979, 
as amended at 44 FR 66195, Nov. 19, 1979; 52 FR 4582, Feb. 12, 1987; 58 
FR 55006, Oct. 25, 1993; 59 FR 2469, Jan. 14, 1994; 59 FR 15113, 15114, 
Mar. 31, 1994; 62 FR 54547, Oct. 20, 1997]