Rigid Foam Insulation Panels/siding
Hi, my garage gable has a southern exposure, and receives a beating from the elements in the winter. I am replacing the old 4×8 panel siding with a similar product (Pre-primed LP Smart Side). The garage is currently an un-insulated 2×4 structure, but I do intend to insulate it in the next few months. My question is:
I wanted to increase the R value of the gable wall by:
1. Applying 4×8 OSB panels to the raw exterior studs
2. Applying Tyvek vapor barrier.
3. Applying rigid foam insulation panels on top of the Tyvek covered OSB
4. Applying furring strips to act as a venting system prior to applying the final exterior siding.
Is this a good idea? Or should I just add to the exterior of the 2×4 studs to create a deeper interior cavity to insulate the gable wall?
If the rigid insulation idea is viable, does anyone know of a product specifically recommended for this purpose, all the hardware stores that sell DOW or Owens Corning rigid panels say they are not sure if the product is intended for this application.
Thanks.
Replies
Greetings Seattle,
This post, in response to your question, will bump the thread through the 'recent discussion' listing again which will increase it's viewing.
Perhaps it will catch someone's attention that can help you with advice.
Cheers
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Seattle- If you are going to put foam insulation over your OSB, you can forgo the Tyvek. Tyvek is meant to keep cold winds from getting into the walls, while still allowing water vapor out of the house. If you're going to use foam insulation, that will block said wind from getting in. It will also block water vapor from getting out, which means that your Tyvek will be doing nothing but costing you money.
You mean forget the tyvek and use building paper instead right? Because in Seattle, he's going to need something to keep the rain out besides rigid insulation.
I never liked putting foam on the exterior. Instaed I fur out the interiors with 2x(to catch interior panels) 16" o.c. and the foam between that. I like that way also because you can stand your sheets of rock vertically and all you have to do is tape your troughs and corners, no butt seems at all. Assuming at least that your walls aren't taller than your rock is long.
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In a climate like Alaska's, you are smart in keeping the foam on the inside as most of your vapor drive will be from the inside out. In Seattle, foam on the outside is just as effective as it would be on the inside.
Eliminating butt joints is a good thing too--
Your basic idea is fine. Plenty of houses being built with exterior foam. As someone else said, you can skip the tyvek. Use polyisocyanurate foam panels (these are typically foil faced on both sides) and have a slightly higher R-value than the blue or pink foam. Use at least 1" thick, preferably 2" or more. I'm not familiar with the siding panels you are planning to use but the furring is a great idea to create a drainage plane. Felt over the foam can't hurt, but probably isn't necessary if the siding does its job.
Thanks
Spray foam (icynene) between studs.
In Seattle I'd just put the Tyvek on the outside and fiberglass batts (followed by drywall/OSB) on the inside. (This is a garage, after all.) Your main comfort improvement will be from cutting out air infiltration.