pat man
3/16/2009
Hello I have been doing research on metal roofing installation with rigid insulation on top of T&G decking. Have Cathedral ceiling below, with open beams and deck. Will apply ice shield at the eaves and then the rest of roof with Resistor Plus underlayment directly over deck. Nail 2x4's parallel with roof slope 24 inches apart and snuggle fit 2 inch thick Cladmate(2ft x 8ft sheets) in between, seal all joints and then nail 1x4 strapping across 2x4's creating air space required . Then procede with installing metal panels , flashing ,etc. Would you say this would be an appropriate technique. Thx Pat
Guest User
3/18/2009
Before we put the ISO (rigid insulation) on, we band the roof with the 2x4's, you have to have them going up the rake also. We cut our ISO in half length wise using a table saw. We then put on the ISO butting it against the 2x4 at the bottom. We then butt the next 2x4 against the ISO going across the roof. We alternate it to the top. This keeps you from having to cut the ISO to fit between the 2x4's yet it is still inbetween the 2x4's.
pat man
3/18/2009
What? why would I cut the rigid insulation? they are already 24 inches wide by 8 ft length. If I am nailing my 2x4's 24 inches apart I do not need to cut them, right? BUT the real question is, do I put the synthetic underlayment under the rigid insulation directly on the T&G deck? My ceiling underneath is open beams and the roof deck planks will be left exposed , why i want to insulate from outside the roof..thx
Guest User
3/18/2009
some rigid insulation comes 4x8 sheets. just guessing!
pat man
3/20/2009
Can we put synthetic underlayment directly on top of T&G deck and is this type of underlayment a vapor barrier. thx
Guest User
3/21/2009
Any underlayment works as a vapor barrier. All I have ever seen or used is ISO in 4x8 sheets.
pat man
3/23/2009
Hi Wade In my area in Quebec we have a product made by the DOW company called Cladmate sold in sheets of 2ftx8ft to deal with our harsh cold climate. This product is more permeable than most extruded polystyrene products, and is not classified as a vapour barrier. Would you recommend putting the underlayment directly on the roof deck then the rigid insulation on top?
Guest User
5/25/2009
Hi, I have the same type of roof and I was told it's ok to put 30#felt directly over the T&G roof deck. And then install 2" ISO rigid insulation(no 2x4 purlins or strips), another layer of 30#felt and then install standing seam metal roof. I live in Seattle area and have 2:12 roof pitch. Although felt is moisture barrrier(not vapor barrier), I was told it's ok to use felt in pace of vapor barrier. Also my roofer says I don't need a 1" air space since it's going to be water tight and there is no chance of water/moisture trapped under the roof. Does it make sense to you? Thank you for your insight.
Guest User
5/25/2009
H.K. What your contractor told you is fine. You do not have an attic but also, what you have is like a sealed attic and so there is no vents. I saw on another post on this website where Todd addressed this not too long ago. We do use purlins because of the compressibility of the ISO board. Without base plates under each screw it is extremely easy to overtighten a screw and cause more oilcanning in your roof. The purlins give you a solid surface. [email protected]
Guest User
5/27/2009
Do I still need a ridge cap installed even though there is no attic and soffit? Thanks again.
Todd Miller
Isaiah Industries, Inc.
6/1/2009
The roof will require some kind of ridge cap, yes.
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