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Fire Rated Ply.

Keystone

Sawhorse
Joined
Feb 23, 2010
Messages
1,062
Location
Lehigh Valley, Pennsylvania
Townshouse developement, side by side units.
Lumber supplier shipped out unrated ply for the 4ft fire separation and OSB for interior roof in fill.
It involves a National Production Bldr. so they have 3 six pack units built and shingled.
Bldr wants to apply No-Burn or similar product to underside of roof sheathing as a remedy.

My opinion is a hard NO, the rating from sheathing is from both sides, top and underside.
Fire rated spray from the underside only protects just that, the underside.
We would still have a minimal unprotected narrow section of sheathing between party walls and no protection form the top side.

I believe the bldr is now speaking with its numerous Licensed D.P.’s...

Thoughts, Opinions?
 

steveray

Sawhorse
Joined
Nov 25, 2009
Messages
8,802
Location
West of the river CT
Assume you are talking about this section? Read to the end of #2...which got cut off in my cut and paste...

R302.2.2 Parapets for townhouses.

2. Where roof surfaces adjacent to the wall or walls are at different elevations and the higher roof is not more than 30 inches (762 mm) above the lower roof, the parapet shall extend not less than 30 inches (762 mm) above the lower roof surface. Exception: A parapet is not required in the preceding two cases where the roof covering complies with a minimum Class C rating as tested in accordance with ASTM E 108 or UL 790 and the roof decking or sheathing is of noncombustible materials or approved fire-retardant-treated wood for a distance of 4 feet (1219 mm) on each side of the wall or walls, or one layer of 5 /8-inch (15.9 mm) Type X gypsum board is installed directly beneath.....

Typically we would not really protect/ rate the roof from the outside...
 

classicT

Sawhorse
Joined
Aug 2, 2017
Messages
1,930
Location
Washington State
Fire seldom burns downward. The roof covering should already be a Class C anyways.

Not sure I am a fan of the spray on treatment. I'd rather follow the prescriptive route outlined in 2018 IRC R302.2.4 w/ the 5/8" Type X on the underside. Note that this is the same section posted by Steveray, but most likely from a different year or state amended. Posting default 2018 IRC as follows.

R302.2.4 Parapets for Townhouses
Parapets constructed in accordance with Section R302.2.5 shall be constructed for townhouses as an extension of exterior walls or common walls in accordance with the following:
  1. Where roof surfaces adjacent to the wall or walls are at the same elevation, the parapet shall extend not less than 30 inches (762 mm) above the roof surfaces.
  2. Where roof surfaces adjacent to the wall or walls are at different elevations and the higher roof is not more than 30 inches (762 mm) above the lower roof, the parapet shall extend not less than 30 inches (762 mm) above the lower roof surface.
    Exception: A parapet is not required in the preceding two cases where the roof covering complies with a minimum Class C rating as tested in accordance with ASTM E108 or UL 790 and the roof decking or sheathing is of noncombustible materials or fire-retardant-treated wood for a distance of 4 feet (1219 mm) on each side of the wall or walls, or one layer of 5/8-inch (15.9 mm) Type X gypsum board is installed directly beneath the roof decking or sheathing, supported by not less than nominal 2-inch (51 mm) ledgers attached to the sides of the roof framing members, for a distance of not less than 4 feet (1219 mm) on each side of the wall or walls and any openings or penetrations in the roof are not within 4 feet (1219 mm) of the common walls. Fire-retardant-treated wood shall meet the requirements of Sections R802.1.5 and R803.2.1.2.
  3. A parapet is not required where roof surfaces adjacent to the wall or walls are at different elevations and the higher roof is more than 30 inches (762 mm) above the lower roof. The common wall construction from the lower roof to the underside of the higher roof deck shall have not less than a 1-hour fire-resistance rating. The wall shall be rated for exposure from both sides.
 
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