The Old FRT is Gone, but Truss Damage Remains by John Bouldin

Remember the 1990's and the older-style FRT problems we were constantly writing up? Once in a while, we see reminders of that old FRT and may overlook the implications of it. The below photo shows a town home roof where the old FRT was replaced long ago, but there is still clear evidence of truss and connector damage that are a significant concern.

At least two major issues have way outlived the FRT plywood itself; first, the deteriorated top chord of the truss itself – this was what caused the original plywood failure - and second, the corrosion of the gusset plate. A third possibility is the nails that secure the replacement sheathing to the top chord may continue to corrode from the FRT chemicals. The combined effects of this residual damage are difficult to quantify, but that is not our job. We do, in my opinion, need to inform our clients that such trusses are deteriorated, and may not perform up to original design specifications.

This is another example of the law of unintended consequences. While the original risk of plywood sheathing failure may no longer exist, structural compromise of the roof support system may.

About FRT Plywood
FRT stands for "Fire Retardant Treated" plywood. Only the earlier generation of this product line was highly problematic, and most of that has long since been replaced, as it was installed from the late 1970’s through the mid 1990’s. The current FRT plywood in use today does not have the same problems as this older style. The older FRT tended to cause wood fibers in the plywood to deteriorate prematurely (when exposed to high temperatures such as are found in attics), causing plywood failure – usually within four feet of the party walls in attics of multi-family structures. The older FRT tended to darken in color to a dark chocolate brown color, and it is common to see it shedding wood fibers onto the insulation of the attic. It also caused the tips of the roofing nails to corrode. As the article shows, this wood deterioration and metal corrosion can spread to the trusses and gusset plates as well.

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