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Cedar wall shingles and rain screens

Wondering what's the better way to make a rain screen is. First option- on the exterior of the studs I'll have 2" of polyiso then felt paper. Then I was thinking of ripping 3/8 plywood into 2"or3" strips and attach them vertically thru the foam into the studs. Then ripping plywood for the horizontal battens for the shingles every 5". Seems like a long time at the tablesaw. Never done this before, might make details around the window tricky?
The other thought- 2" polyiso, felt paper, 3/8 plywood sheets,home slicker then cedar shingles. Two question- will the shingles hold nailed to 3/8 plywood? Any trouble with the plywood on the exterior side of the foam board? Need it there to skip all the furring strips.

Asked by Seth Kelley
Posted Mon, 05/05/2014 - 11:42

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2 Answers

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3/8" plywood isn't likely to have sufficient fastener hold. If you used a high grade baltic-birch plywood it might, but unless you live next to the mill in Estonia it's not going to be cost-effective. Half inch CDX should be fine though.

With a rain-screen gap between the plywood and foam it isn't a problem for the plywood- the plywood can still dry into the gap.

If you made up some 6" square spacers out of 1/4" XPS, gluing them to the polyiso centered on the studs at a 24" spacing, then through-screwed the plywood to the studs 24" o.c. with pancake head timber screws you can minimize the thermal bridging, and have a sufficient rainscreen for keeping the half-inch CDX dry. With 36 square inches of pad at each timber screw you won't have to worry too much about over-torquing the timber screws and compressing the foam, but you still need to pay SOME attention while installing the plywood.

When installing the shingles be sure to use nail lengths that won't penetrate into the polyiso.

Answered by Dana Dorsett
Posted Mon, 05/05/2014 - 12:13

2.
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I would install your 2" polyiso over the sheathing and then another layer of 1/2" CDX over that using long screws into the studs. Then, felt or wrap as you install your windows, then Homeslicker, then shingles.

The time spent ripping plywood or playing around with other small pieces is questionable, and when nailing/stapling shingles you want 100% backing. It will also be a lot easier to install and flash your windows.

As far as nail/staple length, I would be using 1-1/4" or 1-1/2" fasteners (stainless medium crown staples) and they do some through the back of the plywood. As far as I can tell, virtually any exterior foam application gets a LOT of fasteners into the foam as the furring and/or additional plywood AND the siding/trim are installed. Not sure how this can be avoided, or why?

Answered by David Meiland
Posted Mon, 05/05/2014 - 15:56

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