Foam board in place of osb for wall sheathing.

[vhehn]

Foam board in place of osb for wall sheathing.

--------------------------------------------------------------------------------

http://www.dow.com/styrofoam/na/res-us/

http://www.dow.com/styrofoam/na/res-us/installations/foam_over_stud.htm


dow is advising using foam board with metal strap bracing instead of osb for wall sheathing. does anyone have any experience with this method? looking for pros and cons, advice. would hate to have a problem later. it would be hard to fix.

[David]

What climate are you in? How do you plan to insulate your wall cavity? What cladding or exterior finish do you plan to use?

Yes, foam board is a great technology to have. But it has limitations, such as let-in bracing in your framing. You need to tape joints and flash properly.

Not sure about the metal strap bracing. I've only seen capped nails.

Tell us more about your specific location/design, and we can guide you further. Also, do you have an architect or engineer working for you?

[vhehn]

What climate are you in? How do you plan to insulate your wall cavity? What cladding or exterior finish do you plan to use?

Yes, foam board is a great technology to have. But it has limitations, such as let-in bracing in your framing. You need to tape joints and flash properly.

Not sure about the metal strap bracing. I've only seen capped nails.

Tell us more about your specific location/design, and we can guide you further. Also, do you have an architect or engineer working for you?

i am in a cold climate. gets -20 here in winter. it will be a single story ranch 2/6 walls. with brick exterior. i havent decided on insulation type yet. thinking maybe cellulose or blow in foam. dow seems to promote this way of building but i am not sure if its worth taking a chance to save $1000 worth of osb.

no architect or engineer. i am just a smalltime owner builder used to older stick built methods looking at newer ideas.

[rabadger]

I have seen it done but don't like it. Just seams like they are cutting to many corners.

[David]

I'd highly recommend you use the foam sheathing. I'd say probably 2" worth. Being a small town owner builder, I'd highly recommend getting Joe Lstiburek's book Builder's Guide to X Climates (for you, X = Cold, for me, X = Hot-Humid). You don't have to take his word for EVERYTHING, but let's say you'd be well served to understand the principals in play. Air barriers, moisture barriers, vapor barriers, drainage planes, insulation, ... all add up to a lot of information to processs. Get his book. Another good help, though I don't have these yet, are the JLC fieldguides.

If you really do live by "that's not the way they used to do it," then you wouldn't consider the product. And, to top it off, you can use both!

Richard, it may feel like they are cutting corners, but from what I understand, it helps homes up north to push the condensation point past the wall cavity, helping elimate mold issues; the R-6 helps too.

An added benefit, it establishes a drainage plane that you need behind brick. Down here, we keep a 1" gap behind brick to allow some air between the brick and dp, helping it dry. Up there, I believe protocol is to keep the brick next to the dp, but I am not sure. Check here http://www.buildingscience.com/designsthatwork/cold/default.htm for some helpful info, IMO.

Perhaps you understand all this and I am just rattling on. Either way, I wish you best of luck and welcome to the forum.

[vhehn]

I'd highly recommend you use the foam sheathing. I'd say probably 2" worth. Being a small town owner builder, I'd highly recommend getting Joe Lstiburek's book Builder's Guide to X Climates (for you, X = Cold, for me, X = Hot-Humid). You don't have to take his word for EVERYTHING, but let's say you'd be well served to understand the principals in play. Air barriers, moisture barriers, vapor barriers, drainage planes, insulation, ... all add up to a lot of information to processs. Get his book. Another good help, though I don't have these yet, are the JLC fieldguides.

If you really do live by "that's not the way they used to do it," then you wouldn't consider the product. And, to top it off, you can use both!

Richard, it may feel like they are cutting corners, but from what I understand, it helps homes up north to push the condensation point past the wall cavity, helping elimate mold issues; the R-6 helps too.

An added benefit, it establishes a drainage plane that you need behind brick. Down here, we keep a 1" gap behind brick to allow some air between the brick and dp, helping it dry. Up there, I believe protocol is to keep the brick next to the dp, but I am not sure. Check here http://www.buildingscience.com/designsthatwork/cold/default.htm for some helpful info, IMO.

Perhaps you understand all this and I am just rattling on. Either way, I wish you best of luck and welcome to the forum.


thanks. my thinking is that if you use 1 or 2 inches of foamboard as sheathing and then spray a couple of inches of foam you can achieve the same benifits as using sip panels at a fraction of the cost.

[David]

For the most part, I believe you are correct. SIPs I believe are better, but more expensive. What you are doing, I think, will work.

How do you plan to spray a few inches of foam?

[vhehn]

For the most part, I believe you are correct. SIPs I believe are better, but more expensive. What you are doing, I think, will work.

How do you plan to spray a few inches of foam?

i will sub it out. local foam insulation companies will spray 2 inches of polyurethane for 1.85 a sq ft.

[David]

Whew, that's not cheap!

[vhehn]

Whew, that's not cheap!

no, but considering that sips will cost 6-7 a sq ft it seems like the way to go if results are similar.

[TnAndy]

2" of foam board (R-12 ) and regular R-19 fiberglass will give you an R-31 wall.....and for less money than the spray in foam. Pretty darn good wall.

Personally, I like BOTH the OSB and the foam. OSB for structural ridginess, and the foam for insulation.....though I never use more than 1" here. With a well insulated stud cavity, the stud itself becomes the source of heat leaking...foam across the outside cuts that loss a lot.

On the bracing.......I've used the metal strap bracing before....it's ok, and understand you have to "X" brace, because if you don't, and use a single brace, it works fine in one direction and will give in the other......but if I was trying to avoid a panel type sheathing like OSB or plywood, I'd use old fashioned 1x6 'let in' bracing, where each stud is notched 3/4" deep to accept the angled 1x6......makes a HECK of a stout brace.

[pegasush]

The main concern with removal of the ply/osb sheathing is the loss of racking resistance to wind induced loads on the wall. Common construction techniques to overcome these loads are let-in bracing, metal strap bracing, and ply sheathing to walls at corners. Paul Fisette has written a very understandable article addressing the shortcomings of each of these -

http://www.umass.edu/bmatwt/publications/articles/bracing_foam_sheathed_walls.html

For example, the article indicates that metal strap bracing delivered 1,500 lbs lateral resistance, while FHA minimum standard is 5,200 lbs.

I know that metal strap x-bracing with foam sheathing was reasonably popular here 20 years ago, and is very rarely found now. I will not construct using strap bracing.