Add insulation over concrete?
seiyafan
| Posted in General Questions on
The walls of the first floor of my house is half concrete half drywall (picture attached). It’s finished on the inside but I don’t know how much insulation was there on the lower part.
I am planning to add Roxul Comfortboard IS (R8) directly to the outside of the concrete surface. And to make things even easier for me I just want to use polyurethane glue instead of concrete nails/screw. Does this plan sound okay? Is there anything else I need to consider before doing it?
Any suggestion is appreciated.
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Replies
Joe,
Most people would use rigid foam (EPS or XPS) in this location, but I suppose that mineral wool would also work. Regardless of which type of insulation you choose, the above-grade insulation has to be protected from physical abuse with a protective layer like pressure-treated plywood, fiber-cement panel siding, cement board, or stucco over wire lath.
I don't think that you can attach mineral wool insulation with an adhesive. I would use TapCon fasteners to hold the insulation in place. These TapCon fasteners would also hold the protective material in place.
Don't forget that you will need metal Z-flashing to make the transition between the bottom of your siding and the top of the rigid foam / protective material.
Thanks for your suggestion. I am just curious what's the purpose for the metal flashing? water drainage?
I think glue would stick to mineral wool really well, but I think that the mineral wool would pull apart and fall off.
Yup, Z flashing so any water running down the siding or landing on top of the insulation runs off the flashing not into the insulation. Make sure its angled down a bit away from the house so the bottom of the siding doesn't sit in a puddle.
I think mineral wool is a good idea in this application to help allow any moisture wicked up from the ground to evaporate.
I see, so I should insert the Z flashing under the siding and secure with screws right?
Joe,
In many cases, friction alone is all you need to secure this type of Z-flashing.
I just had an idea, instead of using the flashing can I fill the gap with spray foam?
Joe,
Canned spray foam is not waterproof. You need metal flashing in this location.
Great, thanks!