I’m trying something new on an addition I’m building (I’m a DIYer). The addition has a shed roof and no joists. I’m in Canada and am venting the roof by installing XPS panels (cut down from 24″ wide) to fit between the 24″ OC rafter bays held off the underside of the roof deck by 1″ (using 2″x2″ blocks of 1″ XPS). The vent is Cor-a-Vent’s Roof2Wall thingy.
I’ll then add FG batts to insulate the rest of the rafter depth (x8’s) and drywall.
It’s cold now (around freezing) and I noticed that when I opened the door to the addition and let house heat in the XPS panels immediately started to squeek. Some sort of differential expansion thing. It happens right away and is very noticeable. Quite surprising.
Does XPS have a much different thermal coefficient of expansion than wood? Is there any risk that I’ll hear squeeks coming from the closed-up ceiling at dusk when temperature drops bring cold air through the soffit vent into the day-warmed vent space? I have visions of my DW and I sleeping in our new addition on the first night after completion and her saying “Hey, do you hear that squeeking sound coming from the ceiling?”! 🙂
Edited 11/19/2007 8:22 pm ET by canoehead2
Replies
If the squeaking is really immediate upon entering the room, I'd bet that it's due to air pressure changes when you open the door and not differential thermal expansion. Once you get the bays snugged up with fg batts, the XPS panels won't be able to move around and squeak. I've used XPS panels the way you have described and have never heard squeaks after the assembly is buttoned up.
Good thought about air pressure but although it is immediate it also keeps going for many minutes.
Good to know that others have done this too and haven't had problems with it.
Idon't believe it is the foam that is expanding from heat. It is the limber that is doing the moving.
Once you get finished and moved in, the temp will remain at a steady state and not move.
However, you need to seal the edges of this foam vent system to the rafters with caulk or spray foam, IMO
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
Why do you think the panels need to be sealed? To improve air flow from soffit to roof vent? I will have fg batts below the panels, then poly barrier and sheetrock.
Several reasons.The idea of the kind of venting you are doing is to cool the roof surface. If you create a drafting flow of air there, and the ceiling ios less that a perfect VB finish on the interior, you will suck warm moist air up into that cool space where it will condense and make moisture. Personally, I am not a fan of this style of roof insulation/ventilation. It requires perfection. I'm good but I don't do perfection.I like to run the sheet of foam on the face of the rafter so it becomes a VB where you need it and eliminates the thermal bridging. Lot less work than what you are doing, tho you should still provide the vent flow through
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Got it. Thanks.
Ya know, I was just flipping thru the FHB from this moth or last, and there is an article in there that touches on this. I didn't read it so don't know what he has to say, but it might be of value to you.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Thanks. I'll check it ouy.