Reading the stamp: what Class A means on a fire treated 2x
Every piece of FireProShop lumber arrives stamped. Here is what the building official reads on it, what the framer should know about it, and why the stamp says nothing about incising.
A framer picks up a stick of our Douglas Fir and sees two things: a grade stamp and a treatment stamp. The grade stamp is the one he already knows. The treatment stamp is the one the building official is going to ask about, so it is worth knowing what it says and what it does not.
The report behind the stamp
The stamp points to DrJ TER 2504-101, the technical evaluation report for MFB-34 EPA Safer Choice Fire Retardant treated wood. The report is what lets the lumber be accepted as an alternative to pressure-treated FRTW under the IBC and IRC. The numbers behind it come from ASTM E84 run on the extended, thirty-minute schedule and from ASTM E2768: a flame spread index of 25 or less and smoke developed of 450 or less. That is the Class A line.
Hand the report to the inspector at rough frame and the conversation is usually short. Hand it to your risk manager and the conversation is usually shorter.
Why the wood is not incised
Pressure-treated FRTW has to get the chemistry into the wood, so Douglas Fir is typically incised to get it in and the design values take a reduction for it. MFB-34 is a topical coating applied at the mill. The wood is not incised. Allowable design stresses in dry use are the same as they were before treatment, which is why the engineer does not have to touch the framing plan when a project switches over.
Bright uncoated steel nails are permitted under the report's conditions of use. Your crew cuts, nails and hangs the material the way they always have. The only thing that changes on the jobsite is the stamp.
What the stamp does not cover
The stamp covers the stick it is on. It does not cover the field cuts, the blocking somebody grabbed from the untreated pile, or the exposed interior lumber after the walls go vertical. That is what the second layer is for: the framer you already hired sprays the interior with MFB-31 before windows and mechanicals go in. The application record for that spray goes in the close-out package next to the evaluation report.
If you want the stamp, the report and the test standards on one sheet, the spec sheet has them. If you want to talk through how it fits a specific framing package, send us the takeoff.
