(04-17-2022, 06:37 PM)Thronester Wrote: Does anybody know why the county is requiring plywood sheathing on roofs now? Is it a structural thing? I read the code and can’t find it anywhere. I figured I’d ask here before calling the county directly. Thanks in advance.
Three or four decades ago, the plywood decking wasn't required at all. It was just rafter/truss + perlins & add tin. Then several decades ago, we had some hurricanes and everyone went nuts about roofs flying off. So, loads of Simpson fittings and then plywood decking.
However the decking was expensive and folks didn't like it. A contractor used the criss cross metal strapping and that was a good replacement for the roof decking for awhile. I thought it was a bit odd that they never really had very many dimensions for the strapping. It wasn't like at 4' o.c. or anything, just some metal strapping up there somewhere. Some roofs had the strapping at 4', some at 6' some just had one big 'X' and called it enough. Now, the County has decided that's actually not good enough and we're back to the plywood decking again.
The rafter/ truss spacing has been getting smaller, although a lot of that has to do with what's used to span between them. Way back when, it was 2x4 rafters at 5' o.c. w/ 2x3 perlins @ 3' and aluminum roofing. Much lighter than the current metal roofing. The old galvanized tin roofs were much heavier so the rafters became closer together. The current metal roofing is pretty light, but the rafter/trusses haven't gotten any further apart. However, the numbers used to size lumber have changed in the past twenty years so now the same dimension of lumber can't span the same amount that it used to. Probably the difference between old growth timber and the newer faster growing species of trees.
Other than the roof decking, the foundations have changed a lot, too. Along with more engineered hold downs and shear walls. About every ten years there's usually some sort of upheaval in required construction methods.
After the Maui fires, I'm expecting to see residential fire suppression systems required sometime soon.
Kurt Wilson