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Going to reside house. Good time to reinsulate exterior walls…but with what?

user-1035959 | Posted in General Questions on

I’ve got some plugs in the siding now that indicates blown insulation was used. I don’t know if cellulose or fiberglass was used, but my walls are COLD. I have already talked to my siding contractor about 4 inches of foam board and a layer of house wrap. Would it be overkill to add additional insulation inside the walls either on top of the existing insulation or by removing and replacing it? Spray foam insulation is all the rage right now, but the cost is substantially higher than cellulose or fiberglass. Are the benefits of spray foam inside the wall cavity negligible if I already have 2 layers of foam board taped well at the seams and a layer of house wrap? Thanks!


  1. GBA Editor
    Martin Holladay | | #1

    It's hard to know why your house feels cold. It could be because your wall insulation has defects, as you suspect, or it could be due to a different problem entirely -- for example, air leaks in your basement and top-floor ceiling.

    If you want to know more about your home's defects, you should hire someone with a blower door and an infrared camera to perform an energy audit of your home. That's always a good idea before you invest in new insulation.

    A blower door test might reveal that air sealing work is the most important measure for your home. A thermographic inspection might reveal flaws in your wall insulation -- or might reveal that your wall insulation is just fine.

    After your energy audit, you can proceed with your plan to install 4 inches of exterior rigid foam and new siding on your walls if you want -- and if the energy audit confirms that your plan makes sense. If you go that route, I doubt if it will make any sense to remove the existing cellulose in your walls.

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