Proper way to staple up insulation batts in flat roof?

Question

Hi all:Asked this before but didn't get a reply that specifically addressedthe question so I thought I'd try again.I'm putting up fiberglass batts in a flat roof, i.e., the ceiling isremoved so I'm working inside the house.  The roof joists are nominal2 x 10's.  The insulation that was there before had been pushed upinto the cavity between joists and the flanges on the faced batts wasstapled to the wide face of the joists, just above the lower edge ofthe joists.My instinct is to staple the flanges on the narrow edge of the joists,overlapping flanges to create a more secure moisture barrier.Is one way of doing the stapling better than the other?  If so, howcome?Thanks.Tom Young

dpb · Accepted Answer

...You already answered your question albeit the difference is minimal.--

Tony Hwang · Answer

Hi,Main thing is to keep the air leak(thru any gap) to minimum.Whatever makes air tight.

Bob F · Answer

I'd be tempted to add a layer of plastic before re-installing the ceiling to really seal it.Would that meet code?

Tony Hwang · Answer

Hi,Vapor barrier?

Rudy · Answer

Thats the proper way unless the air space above the batts is vented somehow. You dont want to create an unvented air space above your batts which might be the case in a flat roof. If the batts are placed up against the roof sheathing, you dont have to worry about venting.

When they built our home in the AZ desert, they "wired" the R-30 batts up against the roof sheathing between the web trusses.

Joe · Answer

You didn't get the answer you wanted so you're asking again? Rereadthe replies.Joe

TomYoung · Answer

No, I said I didn't get an answer that really addressed my question.Go read the *one* reply at see if you don't agree.Tom Young

Bob F · Answer

Yes. And seal out any potential leaks.

Proper way to staple up insulation batts in flat roof?

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