(a) Separation requirements. (1) Attached manufactured homes shall be separated from each other by a fire separation wall of not less than 1-hour fire-resistive rating with exposure from both sides on each attached manufactured home unit when rated based on tests in accordance with ASTM E119-05 (incorporated by reference, see § 3280.4).

(2) Fire-resistance-rated floor/ceiling and wall assemblies shall extend to and be tight against the exterior wall, and wall assemblies shall extend from the foundation to the underside of the roof sheathing.

(b) Fire separation penetrations. (1) Fire rated fire separation walls must not contain through penetrations or openings.

(2) Membrane penetrations for electrical boxes are permitted on the living side of the wall under the following conditions:

(i) Steel electrical boxes not exceeding 16 square inches may be installed provided that the total area of such boxes does not exceed 100 square inches in any 100 square feet wall area. Steel electrical boxes in adjacent fire separation walls must be separated by a horizontal distance of not less than 24 inches.

(ii) Listed 2-hour fire-resistant nonmetallic electrical boxes are installed in accordance with the listings.

(iii) No other membrane penetrations are allowed.

(c) Continuity of walls. The fire separation walls for single-family attached dwelling units must be continuous from the foundation to the underside of the roof sheathing, deck, or slab and must extend the full length of the fire separation walls.

(d) Parapets. (1) Parapets constructed in accordance with paragraph (d)(2) of this section must be provided for attached manufactured homes as an extension of fire separation walls in accordance with the following:

(i) Where roof surfaces adjacent to the fire separation walls are at the same elevation, the parapet must extend not less than 30 inches above the roof surfaces.

(ii) Where roof surfaces adjacent to the wall or walls are at different elevations and the higher roof is not more than 30 inches above the lower roof surface, the parapet must not extend less than 30 inches above the lower roof surface.

(A) Parapets must be provided unless roofs are of a Class C roof covering and the roof decking or sheathing is of noncombustible materials or approved fire-retardant-treated wood for a distance of four feet on each side of the common fire separation walls; or one layer of 5/8 inch Type X gypsum board or equivalent is installed directly beneath the roof decking or sheathing for a distance of four feet on each side of the fire separation walls.

(B) A parapet must not be required where roof surfaces adjacent to the common walls are at different elevations and the higher roof is more than 30 inches above the lower roof. The fire separation wall construction from the lower roof to the underside of the higher roof deck must not have less than a 1-hour fire-resistive rating. The wall must be rated for exposure from both sides.

(2) Parapets must have the same fire resistance rating as that required for the supporting wall or walls. On any side adjacent to a roof surface, the parapet must have noncombustible faces for the uppermost 18 inches, to include counter flashing and coping materials. Where the roof slopes toward a parapet at slopes greater than 2/12 (16.7 percent slope), the parapet must extend to the same height as any portion of the roof within a distance of three feet, but in no case will the height be less than 30 inches.