Adding Wall Insulation

By: Bill Kibbel , Contributing Writer
In: Old House Construction, Home Improvement Tips

Is it worth all the effort?

We live in a home built in 1915.  Of course it doesn’t have any insulation.  I was doing research and just read your tips on insulating a finished attic.  Do you recommend adding insulation into walls of old homes?  If so, what type is best?

If an older home is undergoing major renovations that include opening up the exterior walls, adding wall insulation can be done rather easily and inexpensively. It can also be installed properly to prevent issues with uneven distribution and moisture condensing. If you’re considering blowing in insulation into finished wall cavities, then no, I don’t recommend it.  Given the opportunity, I try to talk folks out of doing it. That doesn’t mean that I don’t recommend any improvements to increase efficiency. I just try to advise efforts that are cost effective and don’t significantly alter the historic character of old homes.

We know an older home like yours was obviously built without insulation. The people that built it knew it too. It’s possible that your home has some design features that optimize heating efficiency to some extent, considering the limited technology of that time. A study by the Energy Research and Development Administration (now part of the Department of Energy) showed that buildings with the poorest energy efficiency were built between 1940 and 1975!

Distribution and Cost Effectiveness
One of the issues with blowing in wall insulation is the distribution. It can be quite uneven and with certain methods of old wall framing it can result in significant pockets that don’t receive any product. I’m also concerned about an insulated wall assembly that doesn’t have a vapor barrier.  There’s considerable moisture in the air of a home and without a complete barrier, the moisture can condense inside the wall–not a good thing for the wall or the insulation. The hundreds of holes in the walls that need to be patched isn’t a big plus either.

The other issue with adding wall insulation is the return on the investment. Most studies I’ve seen show that retrofitting wall insulation is so costly that the return is measured in decades, not years, like other home efficiency improvements. For example, I was at a seminar that presented a study using an average size home in Minneapolis, MN. The cost of blowing insulation into the walls would be over $4000.00. The annual savings would be around $160.00. Math wasn’t my best subject but I know if I invest four grand, I’d want to break even before a quarter of a century passes.

Start with Reducing Drafts
For improving efficiency, my personal efforts and money are first spent on reducing drafts. If you can feel cold air coming into the heated area of your home, there’s heated air leaving somewhere else. If you really want to find the points of air infiltration, you can have a firm that uses a “blower door” test your home. The blower creates a negative pressure and air comes in all the leaky points. Using a smoke puffer, the leaks are identified and sealed.

Open attics are the next to focus on. Unlike finished walls, there’s usually access to most areas.  Before adding insulation, be sure to seal any air leaks through the ceiling below, then insulation can be added. Blown-in can usually be easily sprayed or batt insulation rolled out to cover the entire attic. I suggest getting it up close to a depth of 12 inches. Don’t forget to insulate over the access hatch or put an insulated cover over the stairs.

If continuing your improvements, consider adding storm windows, if not present, have your heating equipment serviced, and look into updating/upgrading your heating system if it’s an ancient mass of cast iron bigger than a mini-van.

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