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Community and Q&A

Airsealing and adding rigid foam over old clapboards with no sheathing but under vinyl siding

Rob Wotzak | Posted in Energy Efficiency and Durability on

I’ve got an old (1871) balloon framed two-story house in Connecticut with blown-in fiberglass (probably done in the 80s) behind the old clapboards. The old siding has no sheathing, and the previous owner put vinyl siding on.

I’d like to add at least a WRB/air barrier to the outside and possibly some sort of rigid insulation–either foam or Roxul. I don’t have the money to do new siding, but I feel that it’s reasonable for me to pull the vinyl off without damaging too much of it, adding one or more layers of material to provide insulation and airsealing to the exterior, and then putting the vinyl back on. I’ll figure out the best way to deal with the flashing details around windows and doors, but I’m looking for feedback about cost effective exterior insulation assemblies. I’m mostly concerned with material costs and finding assemblies that are safe and effective from a air-sealing and water-management perspective. I’m not as concerned about labor/time since I’ll be doing the work myself, but I would consider choosing time-saving options if the cost difference isn’t huge.

Here are the ideas I’d considered, but I’m completely open to suggestions:

– some sort of house wrap (what kind?) over the old clapboards with 2-4inches of rigid foam and furring strips over the foam
– some sort of house wrap with 2-4 inches of rigid mineral wool and then furring strips
– Zip-R or other similar “one-step” process
– any other suggestion?

For the rigid foam option, I would consider buying recycled foam, even though I know that the condition and thickness of the foam could lead to a more challenging installation.

I’m open to suggestions, but I figure that I might pull or cut back the clapboards around the perimeter of each wall and add strips of wood or plywood there to make airsealing to the old wall easier and more reliable.

Please offer advice about what I have considered, plus point out any details I’ve missed. Thanks!

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  1. GBA Editor
    Martin Holladay | | #1

    Since you're a former Taunton employee who used to work here at GBA, I'm guessing you know the answer: The right way to proceed is to strip everything to the studs, and install sheathing. But your budget is tight.

    Of the options you listed -- all of which are worse than stripping the siding back to the studs -- the best is the Zip R option, because at least it includes sheathing. But of course the best way to attach the Zip R is to the studs, not through a layer of old clapboard.

    The next best option would be to use rigid foam. Rigid foam is preferable to mineral wool for three reasons: (1) You can tape rigid foam, so rigid foam reduces air leakage more than mineral wool, and (2) mineral wool introduces a new problem, insulation squishiness, which complicates the job more than you need, and (3) rigid foam usually costs less than dense mineral wool.

    Don't worry about what brand of housewrap you buy. The brand isn't very important. What matters most is conscientious installation.

    Are you planning to install new windows? If you will be saving the old windows, you need to come up with a window flashing plan.

    1. JZohio | | #7

      What would the correct order be if it was just ridgid foam? Foam board nailed to clapboard, then wrb, then vinyl?

  2. seabornman | | #2

    I renovated a house with the same issues. I started one side leaving the clapboard and sheathing over it. Big mistake. It took more time, made it hard to nail, and made a wall that varied in thickness, making detailing a pain. After the first side I started taking the old clapboard off. Turned out to be easier than I thought it would be.

  3. GBA Editor
    Rob Wotzak | | #3

    Martin, you're right--I'm quite familiar with what the best options are. And really, when it comes down to it, it probably wouldn't be that much harder to strip the clapboards while keeping the fiberglass in place (from what I've seen in my various remodeling projects over the years, it's packed in there pretty well). I guess I was just hoping to find someone who had success with a simpler solution. After living in this 40-foot-tall, drafty old house for 15 years and not having the means to do a proper insulation retrofit--especially when I spent many of those years documenting the high-quality work of quite a few GBA contributors--sometimes I sure wish I had bought a nice simple ranch house that I could easily strip and wrap with rigid insulation. :-)

    And of course if I take this project on, I'll be pulling the windows and re-flashing.

    One question though: Do you see any problem with doing a partial retrofit? What I mean is that there are some walls on my house that are much easier to deal with (either small 1-story additions, or simple walls with no windows), and it would be convenient to be able to treat each wall as a separate project, eventually getting to them all though.

  4. GBA Editor
    Rob Wotzak | | #4

    Thanks for the feedback, Joel. Yeah, a lot of times we cut corners to "save time" and end up spending more in the long run. I try to remind myself of this every time I start a new project. I guess I'll be stripping my walls down to the studs. Luckily, because of the various jogs in the floor plan of my house, I might be able to do the retrofit in stages, one or two small walls at a time.

  5. GBA Editor
    Martin Holladay | | #5

    I see no problems with doing one wall at a time. (Here is a link to a GBA blog written by an owner, Christopher Peck, who did something similar, one wall at a time, over a period of years: The Big Rewards of a Deep Energy Retrofit. I don't necessarily endorse Peck's argument justifying his big investment, but I'm inspired by his example and perseverance.)

    You wrote, "I guess I was just hoping to find someone who had success with a simpler solution." There are always simpler solutions -- including doing nothing. Sometimes an argument can be made in favor of doing fewer home repairs and spending more time camping and fishing.

  6. GBA Editor
    Rob Wotzak | | #6

    Thanks again, Martin, for considering my problem. I especially like your last statement about the argument for spending less time working on my house and more time doing other rewarding stuff. I'm actually in the middle of restoring an old Kawasaki motorcycle that spent the past 40 years in my aunt's basement. I'm trying to dedicate more time to projects like that these days, and spend more time hanging out with my family too. ...but those house projects are always tugging at my sleeve.

  7. JacobTig | | #8

    I didn’t see this commented yet: by adding insulation to the exterior you are making your walls longer, for lack of a better word, which means your existing siding may not work unless you do custom made corners that make up the difference.

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