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austinbirdman 12-11-2006 10:27 AM

Best Ext. Sheathing: Rigid Foam An Option?
I am working with a handyman adding a 2 story addition to my home in Austin, Texas. (Started as a 500 sf one-story, then we decided to go up another floor.) As this is a homeowner's permit job, I am acting as the GC (key term: acting). The guy I'm working with suggested using rigid foam insulation (the 1/2" kind you can get at Home Despot) for the exterior wall sheathing, which we will be putting up in about a week. Anyone know if this the best option, or even a good option, for Austin—or for anyplace else for that matter? I had been assuming we'd use OSB or something like it. We're a very warm climate, with moderate to high humidity (not as humid as Houston or Louisiana).

I'd appreciate knowing what others have used -- material, thickness, and wrap options -- especially in warmer climates.


wolffhomerepair 12-15-2006 06:18 AM

How do you plan on siding it? I know for up north that won't fly. I would suggest you use a plywood or OSB to give the walls some rigidity. The sheeting is an integral part in giving the wall strength.

austinbirdman 12-15-2006 08:32 AM

We will be siding it with 8 1/4 Hardiplank lap siding. For stability, I've seen suggestions (from links on this forum) of using steel t-braces on diagonal (a form of let-in bracing) on the corners. I guess some people also use OSB on the corners and foam on the rest, but that concerns me about creating different levels of insulation and how that make create pockets for moisture.

austinbirdman 12-15-2006 09:02 AM

Order of Operations - Foam Board, Tyvek, Siding
One more thing - I saw where AtlanticWB said "Actually, the Tyvek (or any brand of 'house wrap') goes on first, then the foam insulation on top of that." Is this true for all cases? He was writing about a particular situation where someone had a bunch of layers of existing material to deal with. But I thought it was the opposite for new construction.

Actually, my question has more parts than that. We are using 8 1/4 smooth Hardiplank lap siding on a new addition. In this case:

- What is the right order: Sheathing (foam), wrap, siding, correct?

- If I put up foam board insulation for the sheating, and tape the seams as instructed, do I even need Tyvek or another kind of house wrap?

- Is Tyvek the best option? I've read posts on the Contractor forum where people say tar felt is better for under fibrecement siding.

- Finally, should I use furring strips on top of the foam board (or OSB if I changed course) to create an 1/2" air barrier between the sheathing and the siding? This is a technique some people advocate, nailing the siding through the furring strips into the studs.

As you can tell, I am bit confused with what's the best practice here. Any advice would be appreciated.

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