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Community and Q&A

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 sheathing intact, we will simply cover the boards with foam board. These are 1″ x 8″ rough-hewn boards. 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 sheathing, 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 | | #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. richmass62 | | #8

      Akos, I followed your suggestion and used a peel and stick house wrap to protect the polyiso from the weather and form a better air barrier. I will confirm that that Vycor Env-S sticks very well to the fibre faced reclaimed polyiso on our house. We even stuck put Vycor on the overhangs. In those areas it helped to put down 1/2 inch foamular with screws first, to insure that there was a surface that the wrap would stick to. The cost of the Vycor was $250 plus tax per 400 square feet, from someone who had surplus on eBay. (If you order from Amazon it would cost about $375 per roll.)

      We didn't use the 2-inch polyiso everywhere because the foam is flexible and needs a flat surface in order for the end result to look professional. Some of the walls had a very uneven surface, given that the sheathing was from 1930. On those walls, on the south side of the house, we added 1/2 inch or 1/4 inch Foamular pieces and chunks of rock wool to fill out any depressions in the wall surface. One of the gaps was big enough to be a shelter for mice, so we were sure to fill that up. Once the wall was free of big bumps, we installed Zip system, the insulated kind, to end up with a totally flat exterior surface. We also uses these Foamular pieces on the west wall to fill some of the depressed areas, prior to installing 2" polyiso.

  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:

  3. richmass62 | | #5

    Quick update on what we ended up doing:

    Each wall was updated differently, the decision was based on what was already installed there, how much room we had for insulation, etc. On the bottom of the wall we screwed some pressure treated strips of lumber into the sill with rubber material in between to act as a base for the external layer and top keep insects out of the foam.

    Here are the sections completed:

    1) small laundry room: removed all sheathing, closed cell spray foam inside the wall, 3", covered this with sheathing and 1" of additional exterior foam. The 10 foot section is under an overhang and there should not be an issue with water getting into the assembly. Since the studs had to replaced with 2x6 in this area, we added a layer of rock wool to fill the cavity before sheathing.

    2) rest of the south wall: installed half inch or quarter inch of foamular with some gaps to level out the wall, then put zip R6 on the wall, so that we effectively have zip r9. Original sheating left in place.

    3) west wall: installed 2 inch reclaimed polyiso. The sheets are separated by 1/4 inch and held on with a This has a carboard backing so we are covering it with Grace Env-S as a weather barrier as was suggested by a commenter

    4) north wall: installed 2 inch reclaimed polyiso and then covered it with 1" of foil faced foam. This is getting covered with Grace Env-S. Because we left on the thick sheathing this section required 5 inch screws to reach the studs.

    5) east wall: removed all the insulation and sheathing and installed foamular within the bay for air sealing the wall, 1/2 inch with foam. Then added 3.5" of rock wool to fill the 4" stud bay. Covered this with Zip R-6.

    Sheets of insulation have been sealed with spray foam and covered with opaque tape. Zip system where the sheets meet wood, and lighter 3M tape where there is a foam to foam seam.

    This has made a huge difference, eliminating the draftiness we had before and also making the house a lot quieter. Also we found numerous insulation gaps. We won't see a savings in our energy bill this year because a section was left to be done in the summer, in the area where we plan to attach an addition.

    The most significant improvement so far was on the west wall where the drywall was completely exposed to outside air, and in the kitchen where there were several gaps in the cellulose. We also found a little "crawl space" under the upstairs bathroom that was uninsulated.

  4. katiesharrowreabe | | #6

    Rich, I am in awe of the work you're putting into this house. I hope the effort to date has been more rewarding than tedious! Will look forward to following along.

  5. richmass62 | | #7

    Sharing a couple of photos. Also I did review our bills. Heating cost came down but we will see the real impact once we get to February 2024. That is because our envelope upgrade was at around 50% complete in January and is probably at only 80% now since we didn't yet touch the corner of the house next to our front door.

    First photo is a front view of the house a few weeks ago. You can see that we have one R30+ wall on the south of the house, this is the laundry room with an extra 1" foam covering up Zip r-6. That is not necessary for wall insulation but the added thickness was needed to cover up the sill and make it consistent all the way around the building. Rest of the wall you see (south wall on left side) is just a standard 4" cavity wall (using old school 2x4 studs) that had board sheathing. Added on top of those boards is Zip R-6 (which includes 1 inch of poly iso) which acts as our air barrier. Most of the effort went into the overhangs which were insulated with 3" of closed cell spray foam after 2" poly was inserted into the rafter bays, so this is an additional R20 or so on in place of what was ineffective leaky fiberglass. After this was done rock wool was added just to fill up empty space before the overhangs were boarded up.

    The second photo shows the rear of the house during the installation of Vycor Env-S. There is a great video that I played for my contractors before installation on the Ana White Youtube channel; she and her husband installed the product on a new home in Alaska. You can see the fiber-faced polyiso that I got second hand from on the left side of photo #2. I covered all of the penetrations and dings in the material with little squares of zip tape. (This is a very important step IMHO because the screws embedded in the wind-lock plastic washers would be exposed to the air otherwise, and would transmit more heat through the wall.) We overlapped the corner of the house around 8". There is already zip tape under the corner.

  6. richmass62 | | #9

    Just a quick update: We finally ordered and installed the windows to finish off the south wall. These are triple pane windows from in Toronto, Canada. Cost of each window was around $550 including shipping. There was one single hung window that was less and a casement window for the kitchen that was more. You can see that we now have giant window sills, thanks to the new thickness of our walls and placement of these windows at the exterior on top of zip system insulated sheathing.

    Also we installed a convertible dryer vent, it switches from an outdoor dryer vent in the summer to an indoor dryer vent in the winter. The hole in the wall for the outdoor vent uses a PVC pipe to traverse the wall and metal on each end so there is no thermal bridge. The indoor dryer vent (Funmas brand on Amazon) would cause the window in the laundry room to sweat like crazy when it was just a double pane window. Now that it is triple pane and we have a super insulated wall the indoor vent works well. We just run our dryer on low for the first 30--45 minute for all loads to better distribute the humidity throughout the house. The dryer exhaust is now triple filtered so I am not worried about plastics getting dispersed through the house, and I am also avoiding the release of the micro plastics into my yard during the winter months.

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