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Wall Insulation - Existing Construction

Hi There!

I've gotten a few quotes to insulate the outside walls of my house (1902 Victorian). The price tag for blow-in insulation is $4,500+ potential expenses caused when they pull the boards etc. to drill the holes.

My question is: What is the expected Energy Savings of insulating the walls? I've tried to find on-line resources, but am either too dense to find what I need, or it's just not easy to find.

The contractor told me that the primary reason to do the insulation is to cut on drafts. We don't have any (many?). And that he expects a 15% energy savings. So if we spend about $2000 on oil (I live in New Jersey) and another $500 for AC (window units). We would be saving $400 per year, or it would take us 11+ years to recoup the cost. Doesn't seem worth it to me. And with the advances in insulation, maybe something better is available in 10 years.

Am I missing something here?

Re: Wall Insulation - Existing Construction

As the cost of oil and electricity goes up, you will of course recoup your investment much sooner.

There is also the comfort factor as the drafts are eliminated and one thing I don't see mentioned much but is a nice benefit is the reduction in sound transference.

Blown in insulation is good but the expanding foam is even better.

Re: Wall Insulation - Existing Construction

What are your electric rates? You could go to a heat pump and go all electric or dual fuel.

THe 15% might be optimistic. IF you still have air movement in the alls, the actual insulton value will be lower. Moisture issues can also be a concern.

The R value of the wall caivity with no insulation is often underestimated as well.

Re: Wall Insulation - Existing Construction

There is a book "From the Walls In" by Charles Wing that would be perfect for answering your question. Unfortunately it is out of print but you might have on in your local library of you might find a used book ******. It explains how to calculate the true R-value of your walls and how much they are costing you each year. It also gives an excellent explanation as to why most people are very disappointed in the savings they actually get from an insulation job.

An uninsulated wall actually has an R-value close to R-5. Filling the wall cavity with R-11 does not bring the whole wall up to R-11. More than 10% of the wall is studs which are unchanged by the insulation. The studs will actually "short circuit" the insulation by conduction heat around the insulation. The end result is a wall with about an R9 to R10.

In a typical house, about 20% of the total heat loss is through the walls. Windows and doors account for about 20% as does infiltration. The floors are good for 10% and the ceiling 30%. Your losses may be different, an actual survey would determine that. If your house is typical, then you would be looking at a possible 10% energy savings by insulating your walls. The 15% figure (even more) is possible if you have a two story house and you have already put a lot of insulation into the attic and have upgraded the windows, doors and the weatherstripping.

Something you should consider is having someone do a thermal image of your house this winter. Often very small heat leaks account for very large losses. For example, you might have a lot of heat loss through your plumbed walls. Heat and warm air can enter those walls through conduction and the holes for the supply and drain lines, rise up to the attic through holes in the top plates for the vent pipes and out through the attic vents. This can account for a large percentage of heat loss in a house that has had the insulation upgraded. It is often overlooked. And that is just one example.

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