[Greenbuilding] Exterior insulation retrofit

jfstraube jfstraube at gmail.com
Mon May 23 18:56:37 PDT 2011

They sure can work but they seem slightly inferior to the standard furring over foam solution.
The biggest concern is that the OSB cannot dry out very well as it is cold and on foam.
1x3 furring strips are able to dry out much better because of the ventilated gap that is formed, and the three sides of drying possible. Solid wood tends to be more durable  than OSB.
Using a single layer of EPS without special joints means you have joints that open up when the EPS gets cold.  Two layers of foam with lapped joints ensure there are no breaks.
The 1x3 has stronger nail withdrawl resistance than 1/2" or 7/16" osb which can matter for high wind loads. 
You can replace EPS (R4/inch) with polyiso (R6/inch) and have a 33% reduction in thickness for the same R-value.

All of these disadvantages are small, and not show stoppers. But all of them add up to being less desirable. And the cost for half SIPS tends to be higher, while the availability is less than standard board stock and 1x3's.

Never could find a reason to spec them or use them myself

On 2011-05-23, at 9:18 PM, Chris Koehn wrote:

> Along a similar vein: this just popped up in Green Building advisor: <http://preview.tinyurl.com/3umzxjq>
> While nailbase is available in different thicknesses, this would appear to be perhaps just a couple of inches. And while I'm not a big fan of OSB, this is attractive from an air sealing and ease of installation standpoint.
> Any comments or experiences?
> Chris Koehn
> TimberGuides Design & Build
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John Straube

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