T1-11 Siding as Roof Sheathing

[JennyNakamura]

Hi Everyone,

Background:
I have designed a simple patio canopy that is 20'x20'. It's like a deck in the sense that it is attached to the existing house wall framing by a ledger and the joists are attached to the ledger. I currently have the roof designed as 2x6 T&G decking spanning the joists at 12" oc with 1/2" plywood on top. The canopy will be roofed with built-up roofing.

Question:
The owner's architect friend was reviewing the preliminary drawings for him, and now the owner is asking if we can replace the decking and the plywood both with T1-11. Is this feasible?

Thoughts:
The framing will be exposed, so I thought the 2x6 decking would be nice. I added the plywood to provide diaphragm action and to provide a surface for roofing. I don't see an issue with the T1-11 because it is plywood with sufficient shear value for this application. Also, the joists are at 12" oc so the span shouldn't be a problem either. I just wanted to get some other opinions in case I am overlooking something, since I've never seen T1-11 used in a horizontal floor/roof type application.

Thanks in advance.

 

[LonnieP]

Jenny,

Yes you can use T-111 for roof sheathing, just make sure it's at least 5/8" thick to insure you have at least 3/8" left for structural purposes and the grooves run across the rafters. NOW a reality check. How are they planning to fasten the roofing down? If they use nails they need to be less than 5/8" long or you'll get what they call shiners (tips of the nails sticking below the sheathing). Not a pretty sight.

Lonnie

 

[Ron]

Jenny...flip the T1-11 over and use the smooth side for the roofing. As for the fasteners, if you don't want them to show from below, use asphalt adhered insulation, provided you don't have significant uplift considerations for the roof.

 

[msquared48]

Problem here...

Normally T-111 is placed with the grooves parallel to the wall studs. For strength here, as the roof usage is more likely to see higher load than a wall usage, place the grooves normal to the trusses/rafters and upside down as Ron suggested.

Mike McCann
MMC Engineering