Hello!
We have an addition coming up that will be sided with cedar shingles. As we want to superinsulate, we are considering 2×6 24oc advanced framing with 2×3 horizontal strapping on the exterior. This would give us several advantages-provide a horizontal nailbase for the shingles better than just the osb, allow 1 1/2″ foam foundation insulation to plane out just behind the shingles, etc. I wonder why the strapping is always detailed to the interior when this seems like a better location for it. Are we missing something? I guess maybe less racking resistance because the osb is not nailed directly to the studs, but it is easy to let in a few braces.
Thanks
Martin
Replies
Strapping was traditionally applied to the interior to allow running electrical wires and limit perforations in the air/vapour barrier without moving it too far into the insulation. Strapping is often used on the exterior when foam over 1" thick is used but is sometimes called nailing strips.
Depending on your location exterior foam may or may not be a wise choice - the question is still open to debate. You may want to include a detail that allows some space behind the shingles to allow them to breath and extend their lifespan.
When foam is applied to the exterior creating an air barrier, the interior air/vapour barrier needs to be re-thought so that the wall has a way to dry and does not trap moisture.
The exterior strapping you suggest will provide a base for the osb, but I don't see how it helps the shingles as it would have to be placed at their exposure (ie 5" to 7") to provide a horizontal nailing base for them.
Hope this helps.
Edited 6/14/2009 6:58 pm ET by fingersandtoes
A lot depends on your climate location.
use advanced search here to read up on Mooney walls
you do need to design for shear resistance = racking
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Take a look at this discussion. It explains how and where to use furring, sheathing, vapour barriers, foam board, and strapping in wall construction, and why.
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