Exterior Foundation Insulation: How to finish
Hi,
We are building a small cottage up in Maine. Our foundation wall consists of (working outwards) 2″ Roxul Comfortboard insulation, 8″ foundation wall, and 1 1/2″ Roxul Comfortboard again. Does anyone know of any products that are compatible with region 6 climate to protect our outer layer of insulation? Originally after extensive research and calls, we figured a fiber cement board would work, but after further discussion, concluded that it’s has a very short lifecyle and a poor decision.
Does anyone have any recommendations that are both, aesthetically pleasing and logical for this climate.
Past possibilities that have been mentioned and not an option: pressure treated plywood, fiber-cement panel siding, stucco and surface bonding cement.
Thanks for your help,
S
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Replies
Sarah,
I'd be interested in hearing the suggestions from GBA readers. One approach -- not particularly easy or cheap -- would be to install cement backerboard with TapCon fasteners. After the cement backerboard is installed, it could be covered with stucco.
Most cement backer board for tile isn't rated for exterior use, and could be damaged by freeze/thaw spalling.
Faux-stucco fiber cement siding would probably work, assuming it's suitable for ground contact.
Sarah,
Why not avoid the problem, additional work and expense by moving all the mineral wool to the inside? Concrete is a tough, maintenance free material which is ideal for the demands of ground contact.
Agreed - why are you bothering to insulate the exterior?
I'm not sure how well cement backerboard would hold up under ground contact and multiple freeze-thaw cycles. But if you do go that route, you could probably attach it at the top to the sill before backfilling and have the soil keep it tight to the Roxul.
Otherwise, how about chicken wire & stucco? Or build a cedar screen with a sacrificial layer at the bottom. We did that in a job a few years ago in Falmouth. From the rejected choices I assume you're trying to avoid products with nasty content.
I don't think moving it to the inside is a good idea. That will result in cold concrete. Interior moisture will go through the mineral wool and condense on it. In fact, I'm a little worried about that even with the design as is. I'd be more comfortable with foam in the inside.
Decided to bounce this thread to see if anybody has a solution.
I'm in Climate Zone 5 and I would like to cover 4 inches
of Comfortboard on the exterior of foundation; I could have a maximum of 3 feet of exposed
concrete above grade on one side of the home.
This is a detail that we used on a recent home in Western Massachusetts, Zone 5. The foundation in this case was slab on grade, with 4" XPS rigid insulation under the slab and 2" at the slab exterior perimeter. Exterior walls were double framed.
I used the gray FRP recently, available at the Home Despot, I put it inside out so it is a dull finish. Urethane adhesive [sikaflex] at edge trim and urethane construction adhesive for foam to wall and FRP to foam[it doesn't melt the foam]
I happen to own a 'T nailer' which I use to attach the foam to concrete while the adhesive sets
A really under utilized tool for semi structural attachment to concrete
After 4+ years, how has the FRP held up?