Adding 4″ of insulation to outside walls
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| Posted in Green Building Techniques on
My contractor wants to apply framing to the outer walls, then the 3 ” of board insulation into the framing, then the last 1″ layer placed on top of the new wall assembly. I think that the 4″ insulation can be applied to the wall using only strapping glue and 6 or 7″ heavy duty Head Lok screws. by Fastenmaster.
Is this a good method to do this or should I look into other methods?
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Replies
Fastening Furring Strips to a Foam-Sheathed Wall
you should find several diagrams on this site on a common method
fasten foam sheets, generally screws with big washers / possibly some glue. tape edges
then apply furring strips/battens in line with the studs on top of the foam using HeadLok type screws
then siding choice on furring strips
there are specific details for corners, windows, doors, etc you can find on this site
if you run framing on the outside of the walls, you'll be creating a thermal bridge which dramatically minimize the Rvalue gains you could achieve as all that lumber is R1-ish per inch
Thank you for all the information and the very quick replies!
There is an even better way developed by John Straube at Building Science Corp. First install exterior studs on top of, but spaced away from, the interior frame. One good way to do this is to use pieces of PVC pipe as spacers with long screws running through them. When the framework is in place, apply as much closed cell spray foam as you need to achieve your r-value. The assembly should be deep enough to allow a ventilation space behind your siding. The spray foam will give you a continuous air barrier much more effectively than the many pieces of individual foam board.
You can find information at buildingscience.com, for example Insight #48 "Exterior Spray Foam". There is also an article in the latest issue of Journal of Light Construction on the topic.
Spoken like a true spray foam contractor.
Torsten,
The answer to all green building questions is NOT spray foam- which you so obviously believe.
Sprayfoam may be an answer but here it is prohibitively expensive.About 100 feet o basement sill is about $3000CDN
Martin, I had 300' of sill joists sprayed for $500. Open cell Icynene. The best attribute of spray foam is how well it air stops an assembly. The worst is of course it being far from green compared to cellulose.