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Foam insulation in existing stud walls

I'm thinking of having my home insulated with the foam that is inject into the stud spaces. I am in northeast Ohio and the house was built in 1977. I am told that my current insulation is fiberglass R-13. So far I've talked to one contractor and the cost is considerable. Any input that anybody has on this would be appreciated.

Re: Foam insulation in existing stud walls

Inject foam means that holes are drilled into the wall and the foam is piped (injected) into the holes where it expands to fill the void. You cannot do that if you have any other insulation in the void. This can only be done to an empty void.

You can have the sheetrock ripped out, the fiberglass removed and then have the stud bays sprayed with a foam, then you have to install new sheetrock, tape and mud and paint. That gets expensive.

And what do you get for all this in return. Your current wall is 90% R-13 and 10% R-5. The studs make up at least 10% of your wall and they are an R-5. So the simple math says your walls are an average of R-12.2. It is actually a little less due to lateral conduction of the sheetrock, but it takes calculus to figure that out, 12.2 is close enough.

Now with a spray foam, you might get an R-23 in the cavity. I think it will actually be lower than that but this would be the best case. Average R value would then be about R-21 so you would see a 42% improvement in the heat loss through the walls.

Heat loss through the walls only accounts for about 20% of the total heat loss in the average house, so you are seeing a 42% improvement on 20% of your total heating bill, about an 8.4% in all. Keep in mind that heating the house is only part of your utility bill. And heating is not year round, just winter.

So for every $1000 you spend on heating, you could save $84 per year. If you spend $2500 for heat annually, thats a total savings of $210. How long will it take to get your investment back.

Seriously, if you want to save money on your utility bills, have a whole house energy audit done. Look into the hot water and water use in general as part of the audit as well as lighting and appliance options. Ask for an infrared scan to see exactly where the heat is being lost. You may find that you are losing more than that 8.4% through some very small and easily (cheaply) fixed "holes" in your insulation.

Re: Foam insulation in existing stud walls

What was the bid you got from the contractor?
How long do you intend to live in this home?
There must be other less expensive ways to prevent heat loss. An energy audit will show you how.

If it takes many years to recover an initial investment, and you don't think you'll stay in this home long, then don't do it.

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