Windows: exterior rock wool vs. exterior rigid foam
Tauntaun_Guts
| Posted in Green Building Techniques on
Hi All,
I would like to know if there is any consensus on using exterior rockwool vs exterior foam on new construction. Which favors the most straightforward window detail? Which gives you the most flexibility in choice of siding?
Thanks,
Josh
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Replies
Josh,
I am not an expert--just a home owner but I can tell you that in designing our home we felt that rockwool was a better bet. It has a little more "give" unlike rigid foam so it compensates along uneven surfaces. Foam requires over-lap and rockwool does not. Mice and insects like foam and may tunnel through it. The fire resistance and hydro-phobic qualities of rockwool are also very attractive to us.
Cheers!
Lisa
The higher rigidity of foam makes it generally easier to install with reasonable wall-flatness even in thick layers. But you can get there with rock wool too.
With rock wool an "innie mount" on the windows is a lot easier to get right than trying to set them "outie", so if you're looking to have the glass roughly co-planar with the siding rather than co-planar with the structural sheathing foam is a safer bet.
I haven't priced rigid rock wool recently, but a couple of years ago it was a huge up-charge per R-foot compared to foil faced polyiso. But even foil faced polyiso is substantially more expensive than using reclaimed roofing polyiso.