FRT (Fire Retardant Treated) plywood was and is still in many areas required for a fire break at the roofs for multi-family units, such as townhomes, condos, and duplexes. A firebreak is required to prevent a fire from spreading from one unit to another. Some units may have a masonry wall that breaks the plane of the roof. In this case FRT may not be required. Some areas may utilize fire rated drywall built above the plane of the roof. Typically fire rated drywall or masonry are used as a firebreak between units and in the adjacent attics. When the roof sheathing breaks the plane of the adjacent roof lines a separate firebreak is required. This may be FRT or fire rated drywall sandwiched between the trusses and cdx roof sheathing.
There was widespread failure of FRT manufactured throughout much of the 1980's, part of the 1970's. Due to excessive heat and moisture from improper ventilation the sheathing would delaminate, and in extreme cases sag in between the trusses In this state it could not be walked on or roofed over. In some cases, leaks would develop due to this failure, and the entire roof would have to be stripped of the sheathing, and re-sheathed and re-roofed. Signs of FRT failure may include;
- Sagging
- Delamination
- Cracking when walked on
- Dark discolored surface in the attic on the sheathing
- A hairy or furry surface in the attic on the sheathing
- When in the attic push up on the sheathing and hearing brittle or cracking sounds
Most areas still require a fire break, either a masonry wall that breaks the roof surface, a 5/8" fire rated drywall layer under CDX roof sheathing, or even 5/8 fire rated drywall on the ceilings of the top floor. There may be other accepted methods and variations pertaining to local codes. In our area FRT or some sort of fire break is still required by the code. The newer FRT has been successfully updated with a buffer as well as in conjunction with updated attic ventilation.
A problem we are seeing now is where contractors are coming in and stripping off the shingles and sheathing and replacing it with regular CDX. This is basically removing the firebreak on these units, and should be replaced with a proper firebreak.
In cases where the sheathing is sagging, a temporary fix may be used. This involves using 2 x 4 blocks or larger, installed between the trusses, tight to the sheathing, in a ladder pattern. The spacing of the blocks will depend on the severity of the delamination and cracking, typically 24" on center. Another method is to rip sheets of 3/4 cdx plywood the width of the bay between the trusses. This needs to be installed tightly to the roof sheathing. The protruding shingle fasteners may impede this installation. Once the plywood is installed tight to the roof sheathing 2 x 3" cleats are fastened to the sides of the truss to support 3/4" plywood.
