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Wall insulation in an historic home

bHqUcamKme | Posted in Energy Efficiency and Durability on

I have another question on behalf of a customer of our utility. They have an historic home that they are in the process of restoring. They just completed the installation of a geothermal heating/cooling system, and their next goal is to figure out insulation strategies.

There is currently no insulation in the exterior wall cavities. They were planning to not add any insulation during the renovation because they had heard that putting in insulation will cause the paint on their original wood siding to peel. I think there’s probably a way to insulate without that issue occuring, but I’m hoping that someone on this forum with more knowledge and experience with older homes will have suggestions. Thanks in advance!

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  1. GBA Editor
    Martin Holladay | | #1

    1. What's your climate?
    2. What's the wall thickness and wall construction type?
    3. What's the siding?

    In general, the customer is right. Paint lasts longer when walls are uninsulated than when walls are insulated, because escaping heat helps keep siding dry.

    There are ways to make paint last longer: install a rainscreen or install those little wedges at the clapboard laps.

  2. Danny Kelly | | #2

    They installed their HVAC system and THEN are going to decide on insulation strategies? How did they size and design their HVAC system? Bet it may be a bit too big...only a guess though...

  3. bHqUcamKme | | #3

    Martin: We are in climate zone 6A (northern Iowa). I have not actually been in the home...just talking with property owners over the phone. It was built in 1880, so I have to assume it's balloon framing with 2x4 exterior studs. The home still has the original wood lap siding that they have already begun to repaint (see attached picture). Inside walls are plaster and lathe. Total square footage is 4,283 on 1st-3rd floors; 1,640 sq. foot basement that they will also be finishing/conditioning.

    Danny: I told the property owner that their geo system is probably going to be oversized if they insulate and air seal. They installed a total of 12 tons of geothermal; 6 tons of water-to-air where there was existing duct work in the first floor and basement; 6 tons of water-to-water for the second and third floor where they had an old boiler system providing the heat.

  4. GBA Editor
    Martin Holladay | | #4

    I would recommend that they install dense-packed cellulose in their walls, and to be prepared to paint a little more frequently than they did in the past.

  5. Riversong | | #5

    I agree with Martin that the house should be dense-packed and that they have probably oversized the heating system (144,000 btu/hour).

    Too bad they've already begun to repaint their clapboards, which probably have multiple layers of oil-based paint on them.

    If they scrape off all existing paint and repaint with a good water-based primer and water-based finish, the cladding will be able to breathe and the paint will last much longer.

  6. bHqUcamKme | | #6

    What about foam instead of cellulose? Any advantages or disadvantages?

  7. Roy Harmon | | #7

    If you look at the point at which the bottom plate of the house rests on the foundation from the outside, you suould be able to see the bottom edge of the house sheathing. Most likely 1" thick boards installed diagonally. Trim boards and siding installed over it. I have found that the small amount of spacing between diagonal sheathing pretty much eliminates concerns regarding paint adhesion issues after insulating with cellulose. You would have to look under the bottom edge of the siding to see the end grain of sheathing for verification. I've restored many similar homes using cellulose with no paint problems.
    As Robert indicated in post #5~ the more removal that can be accomplished during prep work the better. A good paint job for an old house = 80% prep work & 20% application in my opinion.
    Foam will be difficult to have installed evenly / accurately in this situation.

  8. 2tePuaao2B | | #8

    Here's a product that works incredibly well for old home paint jobs. Peel Bond

  9. Danny Kelly | | #9

    Don't forget to wear your Hazmat suit and follow the new EPA lead renovation law

  10. 2tePuaao2B | | #10

    Absolutely, if you are a contractor doing the work CYA. Home owners are not held to these standards.
    I built a new porch on an historic old house, all new material. A couple of weeks after the project was complete, the owner called me to find out how she should clean heavy dirt off of the new work.
    Turns out the State was doing a Main St. revitalization project and phase 1 was the milling of many layers of built up asphalt. The dirt ~dust from the milling was dark gray and covered the new white paint. When I brushed it with my hand a bit of a sheen appeared. Looked like lead. Took out my EPA approved lead test kit and 8 tests lead positive. Turns out that the lead that used to be in gasoline was a part of vehicle emmissions for many years. Small towns with Main Sts. and cities accumulated the largest amount of these lead contaminated emissions. Overlaying roadways encapsulated the nasty stuff but milling them up with no EPA requirement or regulation contaminates entire facades with levels of lead from early emmissions. I believe that more kids were poisoned by lead from auto emmissions than any amount of lead that used to be in paint. Paint became the scape goat ,and currently the States using road milling processes without lead regulation of any sort are the largest violators/ contaminators regarding lead issues. No one knows though so mums th word.

  11. Riversong | | #11

    My high school sweetie in Michigan went on to start the first Urban Garden movement in the US in Boston in the 70s. To convert a vacant urban lot to garden required removing all existing soil and replacing it with lead-free soil.

    The pleasures of the automobile culture.

  12. GBA Editor
    Martin Holladay | | #12

    Many studies have backed up your observations. Soil in the yards of homes near busy intersections are usually high in lead, and researchers attribute the high levels to the former use of leaded gasoline.

  13. 2tePuaao2B | | #13

    Funny thing about it was that when I recorded this event into the job log and contacted the EPA for advise as to how it should be cleaned up they told me that since there are no laws or rules that apply to roadwork, they could not give a recommendation. How strange was that?It's recorded in my job log that I can not give my client advise about cleaning up the toxic mess that was created by the State of MD. Who is responsible in a situation like this?
    Sorry for getting off topic Curtis. I was mis-LEAD.

  14. Riversong | | #14


    Remember, it was the EPA which insisted that the air in Manhattan following 9/11 was safe to breathe, for the emergency responders and for the public.

    Clearly, the answer is: When the gov'mint is involved, no one's responsible. But the gov'mint can fine a small-time local painter $20,000 for scraping more than 6 SF of interior paint in a 30-day period.

  15. 2tePuaao2B | | #15


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