What is the best way to insulate an old home from the outside?

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Is insulating an existing home from the outside a good solution?

Cate Prichard June 26, 2021Last updated: July 6, 2021

We bought a home that had been recently remodelled - everything about the interior is to our liking. However, we firmly believe the insulation is inadequate. We have been told that blown-in insulation only works for empty walls - our walls have insulation but it does not seem to be enough. Is insulating from the outside by building out something we should consider exploring with a contractor? We have one brick wall and the rest is siding. It seems a shame to waste all the interior fixtures to insulate. Thank you for any advice!

Responses (3)

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Terry Chemij Feb. 19, 2022, 10:26 p.m.

Hi Mike. I'm curious to hear if you tried this method and if it worked? I have ugly yellow siding on the second level of my home on three sides AND our house is freezing in the winter, so we are looking to remove the siding and insulate it from the outside. Best. Terry

Mike Reynolds Feb. 21, 2022, 12:34 p.m.

Hi Terry, which method do you mean? There are a few safe ways to insulate the exterior, which depend on quite a few factors -

Where you live (your climate zone),

How the existing wall is built (is it insulated and is there an interior vapor barrier)

How much space you have to insulate (do you have close neighbors or a driveway limiting how much insulation you can install)

The point being – it’s most common to see people put foam on the exterior, which will conserve heat, but 1 or 2 inches may trap moisture depending on the existing wall assembly, while putting 6 or 7 inches may alleviate that problem. The short story on that is - there is what is referred to as the ‘2/3s rule’ for home insulation. In cold climates you should have at least 2/3rds of your insulation outside of the vapor control layer, which would be the inside of the foam. That keeps the vapor control layer reasonably warm, which prevents moisture from condensing on it. So if you have 3 inches of insulation and put on 6 inches of foam that's exactly 2/3rds and allows your wall to stay dry. If you have 3 inches of insulation and add 1 inch of foam to the exterior that foam will be cold, and moisture can condense. If you give me a few of those details above I may be able help you come up with a plan.