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Update #2 on 1930 house in Northern MA (adding many kinds of exterior insulation all at the same time!)

richmass62 | Posted in Energy Efficiency and Durability on

Well it is time for another update and question on my home upgrades. My last major post “Update on 1930 house in Northern MA (fieldstone wall, insulating, heat pump water heater in basement)” described how we had improved the insulation in the basement and attic and added a heat pump. This greatly reduced our natural gas usage.

Now we have gone one step further by pulling the gas meter entirely and starting an upgrade of our exterior walls.

Removing the meter wasn’t that important to save money, as we had a low gas bill anyway. But it was 100% necessary because we would like to use the location of the gas line for an addition. And it was necessary if we wanted to move in the direction of a net zero home. I have added info on our new replacement heating system as a comment on the original post. But this is only half the story.

The other half is that we still needed to improve our insulation. Even though MassSave thought our insulation is good, the energy auditors don’t bother to actually verify that the existing insulation is continuous. We knew that it wasn’t. The main sources of leakage were the bottom of the first floor wall, where many rodents were able to breach the siding and mess up our cellulose insulation, and the gap between the first floor of the house and the second floor.

The problem is that these areas were inaccessible to firms that do insulation. To access them and see where the real problem lies we had to do some major demolition.

 So after some asbestos testing was completed we hired a firm  to rip off multiple layers of siding so that we could see the original boards cladding our house. Once this was done (completely filling a 20-yard dumpster), we realized what needed to be done to improve the exterior before reapplying siding.

Also we needed to get a better view of the situation from the inside, so we picked a room with an old ceiling and completely gutted it so that we could see our rim joists on the 2nd floor. We ended up with much cellulose on the floor and plaster in the air, so the demolition was followed by a visit from a clean-up company with a HEPA machine, who vacuumed the 92 year old rafters and removed even more cellulose from those old overhangs and soffits that no longer serve any purpose (since the area above the living room has not been an unconditioned attic for over 18 years).

So now we are ready to build our walls back up using the following strategy:

1) on the walls with original siding intact, we will simply cover the siding with foam board. The material of choice is reclaimed 2″ polyiso, which is available locally for about $16.50 a full sheet including the cost of renting a vehicle to pick it up. It will be attached with foam board fasteners and screwed into the pine siding, before furring is applied and screwed into wall studs.

2) in the areas where no original siding ever existed, like a room that used to be a 3-season porch 50 years ago, we will remove all exterior cladding (like plywood as well as 1 inch x 9 inch “ledger boards”) and then remove the old cellulose. Finally we will fill the wall cavity with 3.5″ Rock Wool and cover everything with new sheathing. The sheathing of choice is Zip-R9, but we may have to settle for Zip-R6 because it is much easier to acquire. This gives an R22 wall. that is air sealed (replacing a leaky wall that was around R-13).

3) on the bottom of the wall we will be able to air seal the insulation board directly to the sill of the house. At the top of the wall we have a large overhang so we shouldn’t really need to worry about water getting into the wall.  And our walls can still dry to the inside if there was ever an issue. We plan to use cold cell spray foam to fill up areas in the overhang and around the 2nd floor rim joist that are now uninsulated or badly insulated.

4) removing all these exterior layers is an opportunity to remove windows and reinstall or replace them.  In the end we decided to close off one window and enlarge several others, taking advantage of the original house framing that has much larger windows than what has been installed inside those frames over the years. So we will end up replacing three failing windows with a U factor of 0.30 with brand new units that have a U factor of 0.19 to 0.21.

If people have suggestions about mixing different types of exterior insulation  and then taping the seams properly, please send them. We need to choose sealing tape that is able to handle the seam between fiber faced 2″ polyiso (to be held in place by strapping) and insulated ZIP-R6 , which is to be held in place mostly with screws or nails.

I can send some photos of the house before demo and after demo if people are interested, along with updates as construction proceeds.

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  1. Expert Member
    AKOS TOTH | | #1

    The hard part of the original house is air sealing. Houses that age have plank sheathing, which is pretty hard to air seal without either peel and stick WRB or spray foam. Since you are looking at Zip R for the rest, it would make sense to have the WRB outside the foam, so this is getting complicated.

    The roofing polyiso is usually fiber faced so it won't hold tape well, I would not try to rely on this for an air barrier.

    Your options are:
    -SPF for air seal, polyiso, WRB
    -peel and stick , polyiso, WRB
    -foil faced iso taped as air barrier, WRB

    I know it is not cheap, but I think doing the whole house in Zip R or nailbase for the old section might be simpler.

    The hard part for these types of retrofit is tying the wall air barrier into the rest of the house. Make sure to figure out how you are doing the wall to foundation and wall to ceiling transitions as well.

    If you have air sealed continuous exterior insulation, your rim joist leakage is a non issues, you can save the SPF there and insulate with batts.

    1. richmass62 | | #4

      Thanks for the WRB suggestion. How does that compare to blueskin I wonder? I googled and found this:

      Does WRB save me a step of having to apply a lot of sealant to the gaps between sheets of reclaimed polyiso?

      Regarding the spray foam on the 2nd floor rim joists, that is an interesting idea. But I did not remove any siding from the 2nd floor (that floor is good, it was built in 2004). Just using WRB won't prevent cold spots in floor 2 (fiberglass insulation) from radiating down the exterior wall or from coming into the rim joist area through gaps where the subfloor on floor 2 meets the edge of the house.

      But perhaps WRB is a perfect solution to cover the old soffit area. We have a large vinyl-clad overhang of 14" on 3 sides of the 2nd floor. See attached photos. Under the vinyl is some old plywood style material that is full of holes. Some of the holes are full vents, about 4" x 12", with an attach metal grille to allow air in without allowing mice in.

      So to use WRB in this area we might have to cover the holes from the inside with 2" foam board -- attach some 3/8 plywood to the underside of the foamboard to match the thickness elsewhere -- and finally use the WRB to create a fully sealed surface.

      My goal is not to have a completely tight home because it would greatly add to the expense to strip and re-side our second floor. I think we will be good enough to have a spray foamed basement ceiling, spray foamed attic ceiling, and a first floor that has a continuous air barrier.

  2. nynick | | #2

    My project is similar. Right now we're planning on Blueskin on the sheathing and CC SPF inside.

    What kind/brand of windows are you buying?

    1. richmass62 | | #3

      hi, in response to your question about windows here is my current plan:

      north wall: Paradigm window, efficient option has 0.21 U factor

      south and east walls: reuse and reinstall one window which is still in great shape (Silverline), order 3 new triple pane windows from Canada at for the south wall that offer better solar heat gain

      west wall: uninstall and reinstall existing picture window on top of new zip system (or install the zip around it, if we can make the wall thickness perfect for doing that)

      Blueskin is an interesting product. I googled it and am requesting a sample.
      here is a link to the product for others reading this thread:

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