Moisture in sleeper bays over T&G roof decking?
HoweeLookin
| Posted in Building Code Questions on
8 years ago. The existing clerestory low slope roof had 2x sleepers over T&G decking with insulation between with sheathing and a membrane roof over. the new addition duplicated this and the entire roof was re-roofed with a new membrane. the 2X T&G decking is exposed to the living space below and is dry…no leaks. the owner is complaining of a “Soft” roof and suspects that interior moisture is trapped in the 2X sleeper bays and rotting. any thoughts? EPD
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Replies
Ed,
Well, the only way to confirm the homeowner's report is to visit the site and investigate -- either by walking on the roof (and saying, "Yikes! This sheathing is spongy!") or by removing a section of roofing and checking out what's going on.
It certainly sounds like a classic mistake: using tongue-and-groove boards as a finished ceiling without installing an air barrier above the boards. If that's what was done, air can easily leak through the cracks between the T&G boards, as well as between the 2x4 sleepers and the rigid foam. Once that warm, humid interior air gets in contact with the cold roof sheathing (or cold membrane roofing) above the rigid foam, you'll get condensation and rot.
This type of roof assembly always needs a bulletproof air barrier between the T&G boards and the underside of the insulation if you want to avoid condensation.
A thermal imaging scan will most likely identify a leak if there is one. Contact a building inspection company or a thermal imaging organization for a referral.
http://www.flir.com/cs/emea/en/view/?id=41393
http://projects.flircs.com/distributors/?app=Building
National Association of Home Inspectors
http://www.nahi.org/