Without a stamp how do you know it's FRT plywood?
Fire Retardant Treated plywood is required as roof sheathing fire protection between abutting houses - duplex, condo, or townhouse. It is commonly called "FRT plywood."
You can tell the brand and quality by viewing a stamp. The stamp needs to be visible, by code. Each plywood manufacturer has its own stamp. One manufacturer's stamp is red, so it is hard to miss.
The fire-coded stamp must be present so it is visible from the attic space and can be viewed by the local jurisdictional authority to insure it is FRT and certify that FRT plywood has been used. The Uniform Building Code says this:
A Fire-Retardant-Treated backboard will be designated with a fire-rated stamp “branded” or “stamped” along the edge or center of the plywood — “UL FR-S Plywood 1780 R-7003.”
I always look for the stamp. When I can't see it I have no choice but to note it on the report.
The stamp has a lot of information as well. The A-C is the grade. A means it is a very smooth, and a good-grade veneer on the interior side. C is the grade for the exterior side. An interior grade of C or D is an inferior plywood and costs less. The "Exterior" means that 90% of the plywood has a glue that will not dissolve from outdoor humidity and can be used for roofing.
Yes, there are different glues for different plys! The stamp is on the interior side to demonstrate which side to put DOWN!!
The code requires the local jurisdictional authority to verify that a quality FRT plywood has been used. And the only way to know that is to see the stamp. Sometimes the edge has been colored, but that still does not give the information the stamp would provide.
In this new construction, not only did the plywood NOT have stamps visible anywhere, but it looked to be of different grades due to the different colors of the veneer.
I did not do a pre-drywall inspection or this would have come up then. That is the stage the county would have verified the FRT presence and signed off on it.
Did they sign off on the fact that no stamps, or colored edges, are visible?
At this final inspection I have no choice but to bring this fact up.
THIS IS A BIG DEAL.
Of course, my clients and the Realtor had no idea and had never heard anything like this before. The "supervisor" is maybe 22 years old and I wonder if he has either.
My recommendation: this is one case in which Big Brother is really looking out for us. Fire codes happen because of information learned from fires. FRT plywood and the fiberglass asphalt shingles on top provide great fire protection between units. BUT THE STAMPS HAVE TO BE VERIFIED!
Jay Markanich Real Estate Inspections, LLC
Based in Bristow, serving all of Northern Virginia.
Office (703) 330-6388 Cell (703) 585-7560