question pertaining to constructing a flat roof.

(Shannon C. Trahan, Sr.) #1

when constructing a slope (0.25 /12) onto an existing flat roof’s plywood deck, using tapered 2x4 lumber at 24" on center and 1/2" plywood (with plywood H clips) nailed on top of the tapered lumber … Is it necessary to reinforce the entire perimeter (seams perpendicular to tapered lumber) of the newly sloped 1/2" plywood decking… To strengthen for potential sagging (hence ponding) on top of newly installed torch-down roof covering??
4:27 am

(Russell G. Cloyd, KY LIC #166164) #2

2x4 rafters? How far is the span on the rafters?

(Dave Fetty, CMI) #3

Sounds like trouble.

(Bradley K. Toye, CMI) #4

Sounds like tapered sleepers were used to create a slight pitch on an existing flat roof. I see no reason to block between the sleepers at the long seams of the new roof decking, as long as the plywood is laid perpendicular to the sleepers, and the sleepers are placed over the original joists.

(Shannon C. Trahan, Sr.) #5

2x4’s are approx. 8’ length. Just to reiterate, they are tapered from 2" down to nothing. they’re only being used to create a slope on an existing well built, flat roofs 3/4" plywood deck, supported by 2x8 joist @ 24"oc. Thank you. Best regards, Shannon

(Shannon C. Trahan, Sr.) #6

how so Dave? can you please explain. Thanks for your time. Respectfully. Shannon.

(Shannon C. Trahan, Sr.) #7

Thank you Bradley. That makes perfect sense. I appreciate your input. Respectfully. Shannon.

(Kenton Shepard, CMI) #8

Yep. It’s basically an overlay. Forget the sleeper dimensions, they bear on the underlying roof structure, they’re fine. As long as the ½" sheathing is rated for whatever roof-covering material is being used, which covers about everything but slate, it’s fine. The clips will help support the plywood edges between joists (sleepers), just like on every other roof with 1/2" plywood (or OSB) and H-clips.
I’m pretty sure that blocking the edges of all panels on a roof (or floor) are to improve its performance as a structural diaphragm. Since the primary roof structure is underlying the sloped roof you describe I doubt blocking would be necessary.

(Alan Singer, #16000058241) #9

Next time try tapered insulation, made for just this scenario