Mobile Home Skirting Codes
Building Code Requirements for foundation skirting for mobile home, trailer, doublewide skirting

General Code citations on mobile home skirting

15.58.060 Mobile home Skirting Installation instructions.

A manufactured home must have a skirting around its entire perimeter. It must be installed per the manufacturer’s installation or, if the manufacturer is not specific, to the standards in this section. It must be vented to allow access to the under-floor area per the manufacturer’s installation instructions or per the standards in subsection (C) of this section.

C. Skirting must be of materials suitable for ground contact.

Metal fasteners must be galvanized, stainless steel or other corrosion-resistant material. Ferrous metal members in contact with the earth, other than those that are galvanized or stainless steel, must be coated with an asphaltic emulsion.

Skirting must not be attached in such a manner that can cause water to be trapped between the skirting and siding or trim. The skirting must be recessed behind the siding or trim.

D. The skirting must be vented

as follows except for manufactured homes sited in a flood plain. For homes sited in a flood plain, contact the local jurisdiction for proper ventilation.

Skirting must be vented by openings protected from the entrance of rodents by being covered with corrosion-resistant wire mesh with mesh openings of one-quarter inch in dimension. Such openings must have a net area of not less than one square foot for each 150 square feet of under-floor area.

Ventilation openings must be located as close to corners and as high as practical. Openings must be located to provide cross-ventilation on at least two opposite sides.

E. Access to the under-floor area

of the manufactured home must have an opening not less than 18 inches by 24 inches and must be located so that all areas under the manufactured home are available for inspection. The cover must be of metal, pressure-treated wood or vinyl.

SKIRTING 55. Designing for Live-Load Deflection – Skirting

Source: And from HUD www.huduser.gov/Publications/PDF/Report_DRM.pdf

Discussion

In a traditional pier and tie-down foundation, the sidewalls of the home are supported on the cantilevered floor joists assisted to some extent by steel outriggers.

The cantilever must deflect under live loads until the joists and outriggers deform enough to carry the loads.

It is very likely that the skirting will be installed at a time when the maximum live load is not in place. Therefore, it can be expected that the sidewalls of the home will deflect under design live loads, possibly as much as an inch or more.

Skirting must be designed to accommodate this deflection, which is certain to take place.

There are three ways it can do this:

(1) accept and support the additional loads;

(2) flex out of the way; or

(3) be designed with a slip joint that allows the deflection without loading the skirting. In support of the first option (which is becoming increasingly popular), the MII needs to include the worst-case expected live load that needs to be supported.

In support of the last option, the MII will need to include the separation required to allow the needed flexure under combined floor and roof live loads.

In the case of the expected deflection, resistance to flexure in the floor system occurs as a result of composite action of the joists, floor deck, and outriggers. These data cannot be calculated by the installer.

In the case where the skirting supports the load, however, standard tables could be used, as the loads depend only on the tributary load distance of the floor and on the live and dead loads. As no life safety issues are involved, these could involve only a modest safety factor to prevent material cracking.

Possible Action

Require MII’s to include tables showing the loads that need to be supported by structural skirting (unless the manufacturer chooses to prohibit such skirting); and include the amount of deflection that needs to be accommodated by the skirting if it is non-structural.

Advantages
Provides needed information to the installer for the proper use of a variety of skirting options. The needed clearance for sidewall deflection is now provided by some MII’s.

Disadvantages: Adds some complexity to the MII.

Here, using Florida's mobile home mobile home section 8.8, we illustrate typical code requirements for mobile home skirting.

Florida mobile home codes pertaining to skirting:

8.8 [Mobile Home] Skirting [Requirements]

8.8.1 Construction.

8.8.1.1 Skirting, if used, shall be of weather-resistant materials.

8.8.1.2 Skirting shall not be attached in a manner that can cause water to be trapped between the siding and trim or forced up into the wall cavities trim to which it is attached.

8.8.1.3 All wood skirting within 6 in. (152.4 mm) of the ground shall be pressure treated or naturally resistant to decay and termite infestations.

8.8.2 Ventilation.

8.8.2.1 Ventilation shall be provided for the crawl space with skirting as follows:

(1) At a minimum of 1 ft2 (0.1 m2) of free area for every 150 ft2 (14 m2) of the home’s floor area

(2) Except in arid regions with dry soil conditions, the following shall be permitted:

(a) A uniform 6-mil (0.15 mm) polyethylene sheet material or other acceptable vapor barrier material shall be permitted to be installed on the ground surface beneath the home to further reduce moisture.

(b) Where an acceptable ground vapor barrier is installed and one such ventilation opening is within 3 ft (914.4 mm) of each corner of the home, the total area of ventilation openings shall be permitted to be reduced to 1 ft2 (0.1 m2) for every 1500 ft2 (140 m2) of the home’s floor area.

8.8.2.2 Ventilation openings shall be placed at or near each corner of the home and as high as practicable.

8.8.2.3 Openings shall be located on at least two opposite sides to provide cross-ventilation.

8.8.3 Access opening(s)

not less than 18 in. (455 mm) in any dimension and not less than 3 ft2 (0.28 m2) in area shall be provided and shall be located so that any water supply and sewer drain connections located under the home are accessible for inspections.

8.8.4 Dryer vents,

air conditioning condensation drains, and combustion air inlets shall pass through the skirting to the outside.

Above excerpted from

• HUD MODEL MANUFACTURED HOME INSTALLATION STANDARDS 2003 Edition [PDF] original source: US HUD www.hud.gov/sites/documents/225HUD.PDF
  

U.S. Department of Housing and Urban Development (HUD) - Most of FL is wind zone 2; the bottom-most counties are wind zone

3. Some homes have a "D" sticker added for extra resistance for coastal construction.

The Hernando County clerk posted this guide from the state cap in Tallahassee, Florida

• ORDINANCE NO. 92-5 covering a potpourri of subjects including AMENDING APPENDIX A, ARTICLE IV, SECTION 2(A) (4) (k), PROVIDING FOR NEW MATERIAL TO BE USED IN MOBILE HOME SKIRTING, - and other mobile home provisions hernandoclerk.com/filebrowser/download/1774

No mention of specific fasteners is therein.