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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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  1. 29 Responses  to “Adding Wall Insulation”

  2. Kath Morgan
    Sep 6, 2014
    Yes, retrofitting wall insulation can be costly and needs proper planning. To maximize its efficiency, I would have to agree with you that reducing drafts is a great way to do it. Thanks for this very informative article. There are lots of old houses that need proper adding of wall insulation and this article is a good guide. _________________ Tiptop Insulation In Home insulation installers Adelaide
  3. Aug 8, 2014
    Hi. I am completely ignorant about this topic. My daughter and I own rental property in Southern California's valley area and there is a 400 sq guesthouse built in 1947. In the 70's the owners took it from a pool house with a long porch to a guesthouse that has no roof insulation, wall insulation etc. I bought new energy efficient windows but the house sides go up only 6 ft and the roof peaks at 10 ft. If its 90 degrees outside, its over 100 degrees inside. How do I go about insulating this guesthouse? I can't afford to lose 10 inches of roof space with the short side walls and I was told by a contractor that anything less than 10" in attic insulation wouldn't be worth the money. Is there a paint that helps insulate? Any ideas because the a/c bill is outrageous. Jo Anne
  4. Apr 7, 2014
    The last thing you want is to have insuffieient insulation and have warm air leave your home in the winter, and cool air leave your home in the summer. Not only is is frustrating because you want to be cool in summer and warm in winter, but also because it wastes energy, which wastes money!
  5. samuel
    Mar 21, 2013
    You are right we have to check heated air leaving for improving efficiency. This is really an informative post about insulation. Insulation is really a crucial thing for homes, many thanks for sharing this article. insulation fenton mi
  6. Julio
    Feb 1, 2013
    what type of insulation should I add to a 1840 home?? Regards
  7. Aug 29, 2011
    Polyurethane foam roofing saves our roofs and walls from a great damage. I like the post. Thanks so much for posting.
  8. Aug 29, 2011
    Evangeline, I think you're confused - this isn't TOH (This Old House). Look up at the top of the page. Unlike TOH, I don't write anything that's an attempt to convince folks to waste their money. Unlike TOH, OHW lets me write about what I've learned is best for preserving historic buildings, without being concerned with product advertisers.
  9. Evangeline
    Aug 29, 2011
    You say wall insulation is not recommended but you or TOH advises it in several places at your site.
  10. merrilee
    Aug 29, 2011
    We are renovating a family farm house that was built in 1912, as with the above family.. No insulation at all. we are more than willing to remove the inside of the exterior walls to put in the insulation and then put the walls back in place.(the entire house is made of planks) The attic is enormous, so not so worried about insulating it.. plenty of room to move around in. This house has never had heat/air, so we will be adding a unit in the attic, that will be the easiest to run the duct to each interior wall. Our worry is the floor. The house is on pier and beam, how do you insulate the floor?? Just underpinning? Is that going to be enough??
  11. Aug 29, 2011
    Great post,all rooms except one in our Victorian solid walled semi have been gradually insulated internally over a long period, some nearly 24 years ago. The insulation boards used were either 50mm polyurethane foam / plasterboard laminates (with an aluminum foil layer behind the plasterboard as a vapour barrier), installed by myself, or 30mm phenolic foam / plasterboard laminates (without an aluminum foil vapour barrier), installed by a contractor. However, both foams are closed cell and, AFAIK, impermeable to moisture vapour anyway. As belt and braces I have painted it all with 2 coats of Gyproc Dry Wall Sealer which is claimed to act as a vapour barrier in itself. Clearly vapour can still enter the wall round the edges of the boards and through any perforations. Brian Sound Insulation