Rigid Foam Insulation

THP

I am working on a house plan right now with brick veneer exterior walls w/ 2x4 studs. I typically just draw in 1/2" or 5/8" gypsum on the inside, studs, 1/2" sheating ply., 1" air gap, and then the brick veneer. The builder asked me to change the 1/2" sheating ply. to 1 1/2" rigid foam insulation. I haven't drawn a house with this and I dont really know much about it. Can I just replace the 1/2" sheating with the 1 1/2" rigid insulation, or does it nail to the sheating? Any type of information and help about rigid insulation would be greatly appreciated. Thanks.

-Rainer

Grumpy

The rigid insulation IS NOT going to offer the stability you would receive from the ply. I highly doubt this would meet any code. I MUST be misunderstanding your question.

THP

...that is what I was asking. I figured this, but I have never worked with this material and I wasnt sure. Thanks.
-Rainer

Grumpy

Keep the 1/2 ply and put 1" rigid foam ontop of it.

Marker

One of the drawbacks of foam board is that it provides no barrier to termites, they eat right through the stuff, much easier than you might think. Stay with what works.

eidaj

First I'm not an expert but I did have experience with the exact same situation. I am building a home and found out that the builder uses celotex, foam board, instead of OSB or Plywood. Surprisingly it meets code, at least in michigan it does, but I didn't care I paid extra to have OSB sheathing. Even though I'm not an expert I know it the osb offers way more structural integrity.

Glasshousebltr

Built a 3500sqft home in Roanoke Va. Customer asked the same thing, replace OSB with Rigid foam. We did so, against my advice. Afterward, I could shake the truss webbing and knock crap off the walls.

Bob

PipeGuy

Between 1978 and 1995 the area I live in changed dramatically. One of the things that took place was the invasion of the townhouse. 100's of thousands were built. Except for some of the oldest, which were built in sprawling "planned communities", most consist of aluminum siding over foam board. When wood sheathing was used, which was only up until the late 80's, it was used only at the corners of the end units and around substantial wall openings. I've often wondered what this place will look like if a hurricane ever comes through without losing too much steam. Maybe the gypsum firewalls will hold everything together?

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jscoob1

Weigh the cost and then think about someone being able to braek in your house with a utility knife!

Teetorbilt

Good thing that I missed out on this one.
jscoob, all that it takes to break into a house is a rock. It's not a high tech manouver and cheaper than a utility knife.

NormZ

I'm not a contractor, but both of my brothers are. Around here rigid foam is pretty much the standard. OSB is only used when specifically requested by the homeowner (at an extra cost). Stability is provided by thin metal bracing nailed to the outside of the studs before installing the foam. OSB is usually used near outside corners and around garage doors. Fiber cement siding has also become the standard in recent years.

bountyhunter

I am just north of Andover and have never heard of not using OSB for the exterior boxing. I guess if you are on a tight budget and will not be in the house for more than 10 years, than go for it.

One rule you can ALWAYS live by: "You get what you pay for"

TimWieneke

Just saw this.

THP - here's what you do. You use one sheet of 1/2" plywood (not OSB) at each side of the corners and wall ends and use rigid foam in between. That way the plywood will keep the walls together and square, the corners rigid and you can still use the rigid foam.

Works perfectly fine this way.

Tim

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As Steve the Foreman would say, "Forgive him Lord, for he doesn't know what he's doing."

mdshunk

Around me they often do 2x4 walls with 1-1/2 foam outside so that they can get the required R19 for the walls without framing with 2x6's. Cover that with vinyl siding, and you've just built yourself a big Igloo cooler. Like Teeter says... throw a big rock between the studs and you've just broken into the house. This isn't exactly one of the best construction practices I've seen, but it does completely meet the current IRC for a great portion of the country. Areas with different wind speed considerations wound obviously need fully plywood sheathed.

TimWieneke

Whoa.... hold on. I assumed I read 1/2" sheathing and 1/2" rigid foam - just re-read the first post. 1-1/2" rigid foam? That's very odd....and it eliminates my solution (pays to read the architects specs I guess... ). Yeah - I can't see anything beyond Grump's recommendation of 1/2" sheathing and 1" foam on top (or do that at the corners and have 1-1/2" foam in between corners) if you really want to accomplish that....

Works here in Chicago where we get no hurricanes (ok ok - tornados now and then I guess).

Tim

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As Steve the Foreman would say, "Forgive him Lord, for he doesn't know what he's doing."