Half inch plywood battens for rain screen?
My contractor put up the first three quarter inch 1x4s today and there isn’t quite enough room for my siding around the windows and doors. If I had another quarter inch I’d be fine. My question is will I have a strong enough wall if I use 1×4 half inch 5 ply fir plywood battens over inch and a half roxul using the heco topix therm screws made for inch and a half foam board? I would use three inch siding nails that would go through the battens and into the studs a half inch. We are into this project and the contractor wants to keep going tomorrow morning so I would really appreciate help from anybody out there that can give me a reliable answer. Thanks. Craig McCormack
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Replies
Craig,
Lots of people have used 1/2-inch plywood furring strips to create a rainscreen gap. In most cases, though, the 1/2-inch furring strips are installed on OSB or plywood sheathing (with intervening housewrap, of course), not on continuous exterior insulation.
The problem (as you evidently realize) isn't whether the 1/2-inch gap will be adequate for the rainscreen. It will. The problem is siding attachment.
You haven't told us what type of siding you are trying to install. In theory, most types of siding can be installed through continuous exterior insulation, as long as there is sufficient penetration of the fasteners into the studs, and as long as the siding manufacturer agrees with your fastening method.
So you need to call up your siding manufacturer to figure out whether your plan meets their installation instructions.
This is Craig again. My siding will be LP Smart Side which is structurally strong enough according to some codes to be installed directly over studs with no sheathing. Eight inch lap with six and a half inch reveal. Also the studs are 16".
Craig,
Here is a link to the installation instructions for your brand of siding: LP Smartside Installation Instructions.
According to this LP document, "Penetrate structural framing or wood structural panels and structural framing a minimum of 1-1/2 in."
So, as far as I can tell, your plan for the siding fasteners to go "into the studs a half inch" is insufficient.
Craig, didn't we have a whole discussion about this before you started? It's very common to add exterior extension jambs and sill extensions when doing exterior insulation. You should be able to find lots of details online. It's not that hard to do. I have no problem with 1/2" rainscreen strips, but I would never use them over Roxul.
Michael,
What do you use over Roxul?
Keith, I've only used exterior Roxul on one project. On that project we (Mike Guertin was the builder, for the 2016 Fine Homebuilding ProHome) used 1x4 vertical strapping. A company near me, GO Logic, uses thick exterior Roxul and 2x4 strapping. If I were to do exterior Roxul again I would plan for 2x furring.