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Retiring and will be building a down sized home for wife and I

My question is about construction of the exterior wall. I plan on 2x4 wall on 2' centers, with exterior strapping of horizontal 2x4s on 2'centers. The spaces between the strapping will be filled with cut to fit 1.5" sheet foam, sealed and taped. Then 2 layers of taped and sealed sheet foam, folled with vertical 1x4s attached through foam to strapping (for rain screen), finished with horizontal siding. I haven't built houses since undergraduate school (many years ago), but have been following more current discussion about energy efficiency/green construction. Do any of you with the experience and expertise see a problem with my plan? The home will be in Montana, dry, cold and hot.

Asked by Michael Parnell
Posted Fri, 04/13/2012 - 17:09

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6 Answers

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1.
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Michael,
Lots of people are building wood-framed houses with exterior foam sheathing. The only unusual layer in your wall assembly is the layer of horizontal 2x4s with foam infill between the 2x4s. That's a fussy, unneccesary layer.

I think you don't need the exterior horizontal strapping.

Answered by Martin Holladay, GBA Advisor
Posted Fri, 04/13/2012 - 17:21

2.
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Martin, after reviewing my question I realized I left some information out, sorry. I'm using the strapping in lieu of the traditional ply or osb sheeting layer, to provide structural stability and a simpler/cheaper way to allow my rain screen to attached to the framed wall. Also, I plan on leaving the internal stud cavities empty except for some fire blocking.

Answered by Michael Parnell
Posted Fri, 04/13/2012 - 17:55

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Michael: First off, I am just a diy guy. May I ask if your 2x4 "sheathing" idea has been approved by your code officials? IMO, the time it takes to nail in a couple of 2x4's is not significantly different from nailing in a sheet of 1/2" CDX, and the cost is not that much different, either (especially easy for me to say when it's YOUR money). I would guess that you would need a bunch of horizontal 2x4's to get the racking resistance of a sheet of plywood. And cutting, fitting, and sealing all those pieces of foam? Have you considered a double-stud wall w/ dense packed cellulose? Foam is hardly "green", but it certainly can make a warm house. Have you Googled "Remote wall", if you are headed in that direction? Just thoughts. My wife and I are also building new, but the numbers in my area say dense packed cellulose and a double-stud wall is cheaper (per R value) than foam, and far more Earth friendly. Good luck, whatever you decide.

Answered by John Klingel
Posted Fri, 04/13/2012 - 23:04

4.
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Michael,
The horizontal 2x4s will not provide racking strength. You need diagonal bracing for that.

Answered by Torsten Hansen
Posted Sat, 04/14/2012 - 09:06

5.
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Martin, John, &Torsten
Thanks for the input, I'll be rethinking some of my plans and i'm sure i'll be back for more advise. I'll keep reading all your input to others as well.
Mike

Answered by Michael Parnell
Posted Sat, 04/14/2012 - 19:21

6.
Helpful? 0

michael, the product you want to use is horizontal bracing made by any of the hanger manufacturing companies. it comes in steel rolls and is hammered in flat across the 2x4s and should be code approved. hit their web sites and grab one of their sales catalogs for details. you can also use some of the brackets and hold-downs they make if strength is important or code required, like say keeping a heavy windstorm from lifting the wall off the foundation.

you can also put 2x4 braces horizontally in between each stud inside the cavity, generally one halfway up.

then you can lay foam flat on the wall.

as far as the rain screen, you then just screw in some 1x3 or similar on top of the foam to use as a base to provide a rain screen gap and to nail your exterior siding onto. this strapping would run vertical in the same spots as the studs.

your idea is not only a lot of work, but each board in between the foam is not good for thermal contact lowering the r-value of the wall, wood is R-1 per inch.

Answered by bob coleman
Posted Sun, 04/15/2012 - 12:28

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