From: John Rose <jrose36(--nospam--at)earthlink.net>
Date: Mon, 07 Feb 2000 22:22:03 -0800
Well, Ed - let me take a shot at some answers.
1. Certainly the roofing manufacturer may have his own specs for min. thickness of roof decks. Could be based on attachments for wind uplift. If Factory Mutual Research Corp. (FMRC) is involved (this organization traditionally used by roofing manufacturers), their specs for wood roof decks call for min. 3/4 in. sheathing thickness. But less thickness would be acceptable, in
my opinion. After Hurricane Andrew, where roofing tiles often blew off roof decks due to inadequate attachment (mortar bed "adhesive"), mechanical attachment of tile became more common. Tile attachments in wind uplift tests often call for min. 19/32 in. plywood sheathing. But it all goes back to the roofing manufacturer's warranty and installation recommendations; if
anything less is used, the builder/homeowner risks having the warranty voided. The roof sheathing attachment for wind uplift depends on the wind uplift pressure, and roof deck area where highest pressures occur. The min. attachment schedule is 6 in. o.c. at panel edges, and 12 in. o.c. on intermediate supports, regardless of the type of fastener used; more fasteners might
be required for high wind zones. APA has technical info on roof sheathing attachment for high wind zones.
2. If common wood screws are used for sheathing attachment, the NDS calls for predrilling of lead holes. Do you think any contractor would do that? The best system if screws are to be used, is for self-drilling screws like deck screws. There are several that have ICBO ES approval, even for diaphragm applications.
John Rose/APA, Tacoma, WA
Ed Fasula wrote:
> Today I had two questions the APA couldn't help me out with:
> 1. What is the typical sheathing used for slate roofs with wood trusses @ 2' o.c.? 19/32 will handle the load fine with L/360. But I contacted CertainTeed Roofing, the only ones I could get ahold of, and they have a lighter slate substitute which they require 3/4" sheathing for. Is it controlled by fastening requirements that may vary based upon mfgr.?
> 2. The Architect wants to use screws in the floor. APA says use code approved fasteners... and suggested browsing the ICBO website. Well, isn't that just proprietary screws? What about woodscrews per NDS? I don't need much for shear so all I want is what is typically used as an equivalent to 8d nails. Or does this mean something questionable like sheetrock screws?
> Ed Fasula EIT