[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]