Lol!! “the outer layer of the ply charred and the rest survived perfectly.”
The joist (troopy1 is correct, don’t know why I said beam) is then 2.5mm thick, after the fire has charred the outer laminates; thinner than a hard back book cover! But it will probably have destroyed the cheap pine top and bottom runners, so there’ll be no torsional strength left. It will just buckle.
The glue failing over time was my mate’s first comment, mine was that we need to be careful with the blowtorch. I can see why they’re strong, that it’s a clever design, but I looked at all the knots, felt the breeze flowing through, and thought “too clever by half”.
