GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Upgrading Insulation in an Old House

mmallozz | Posted in Plans Review on

I’ve really learned a ton from this site so far, thank you all so much already, and now it’s time for my first post!

After moving in almost two years ago to my 1912 house with 2001 addition in Massachusetts, we had MassSave tackle the low hanging fruit at no cost to us – air sealing the attic floor, blowing in a ton of cellulose to the attic, and insulating and sealing all the rim joists. During the winter I used a thermal camera and smoke pencil to seal up and better insulate all the weak spots that I could, and took notes on weak spots that I’d have professionals address. Now is the time for me to bring in the pros, and I want to make sure that my plans make sense.

One of the biggest steps will be replacing our painted wood siding with Cedar Impressions shakes, and I decided to get 1″ of exterior foam insulation underneath that, which I believe for my climate zone and 2×4 framing is appropriate to avoid problems with moisture in the walls. The old wood shakes will be torn off to examine the framing and the sheathing for any moisture issues. I’m very excited for +R5 and breaking the thermal bridging on most of the walls (some parts of the downstairs have stucco on the outside). This part is verbally confirmed (no deposit or contract signed yet), and awaiting our other insulation improvements to get started in the next few weeks.

In advance of that I’m hoping to have the following weak spots addressed:
(1) Cavity above front porch and below shed roof. The knee wall between this space and the bedrooms on the second floor has some access doors (I’ve already permanently sealed all but one, greatly improved the sealing on the accessible one, and insulated all), some recessed drawer cabinets (were previously wrapped in plastic sheeting and fiberglass, pretty leaky, I sealed off the drawer fronts with removable caulk for the winter but would like them to be usable), and cellulose in the stud bays. There doesn’t seem to be any intentional ventilation in here (no soffit or gable vents).
(2) Cavity above family room and laundry room and below shed roof. This bit of the interior ceiling (like 5 feet) is insulated with fiberglass, but there is one can light and a laundry room exhaust fan sticking up into this space, both are leaky. I assume that the laundry room exhaust fan, and the adjacent full bathroom exhaust fan, just dump into this space and rely on its soffit vents (shed roof so I assume no ridge vents) to get rid of moisture, which is obviously not ideal. The knee wall shared with the bedrooms above are insulated with fiberglass too.
(3) Cantilevered floors, upstairs is larger than downstairs by about 16″ above the front porch (full length of house) and on the other side of the house (maybe about 10 feet long).
(4) Stud bays that showed as empty, sagging, or patchy in IR scans.

Here are my current thoughts for each based on a couple conversations I’ve had with insulation contractors:
(1) Pull off the plastic sheeting and fiberglass from the recessed drawer cabinets, close them in with rigid foam board and can foam all the edges and seams. One contractor proposed 1 inch of polyiso for this (R 6.5?), and nothing else for the rest of that wall since it already has cellulose. Since this space isn’t useful for anything (too small for storage), is it worth taking up a bit more space and getting say 2-3 inches of open cell foam (this guy proposed all open cell elsewhere) sprayed over the entire knee wall once the rigid foam boxes are in place, to better seal the wall especially where the wall meets the cabinets, and of course to break thermal bridging? Is open cell okay as the outermost layer of the envelope in this spot, as it’s protected from direct water by the roof? The other contractor proposed 3″ of closed cell foam over the entire wall and cabinets, but he didn’t realize that some of the cabinets just have framing and don’t have rigid panels yet, so spray foam directly on those wouldn’t work without an additional step. With these approaches should I add some ventilation to the gable ends or to the soffits? The alternative here would have been to bring the entire cavity into the envelope, but that would have involved insulating up between the rafters as well as the cavity’s floor (above the porch ceiling), and tackling just the knee wall seems simpler with less surface area.
(2) In this case since there is conditioned space to the side of (bedroom knee walls) and below (laundry room and family room ceilings) the cavity, my thought here was to foam the entire roof deck and gable walls, and seal off the soffit vents to bring the cavity into the conditioned space. Before that happens, of course I would make sure that the bathroom and laundry room exhaust fans are routed to proper vents in the nearest gable wall. I believe the rafters are 2×6. One contractor is proposing filling the rafter bays with 5.5″ of closed cell foam to be flush with the rafter bottoms, the other is proposing 9.5″ of open cell foam – though nominally a similar R value (R 36-38), if my math is correct then the open cell approach has over double the effective R value because of 4 inches of foam breaking the thermal bridging (R32 vs. R15, assuming R1 per inch of the rafters occupying 25% of the surface area – 10% seems to bring it to R35 vs. R23). Am I thinking about this correctly?
(3) One contractor proposed 5.5″ closed cell foam, the other 7.5″ open cell foam. Getting a little extra nominal R value out of the closed cell here, but the difference (and the overall effectiveness of both) will be greatly reduced by the thermal bridging here. I’m not seeing a great way to break the thermal bridging in this case, as one has the porch ceiling below it so no space to put anything without that part of the ceiling being out of flush with the rest. On the other side of the house theoretically the entire board could come down and we might be able to sneak in say 1 inch of foam board before it goes back up, or even just foam board plus the aluminum cladding that the siding guy will be using on a lot of the trim if that’s enough to protect the foam, but unfortunately that’s for the 10 foot section of the cantilevered floor rather than the 30+ foot section.
(4) Before the new siding goes on, drill and fill from the outside in each stud bay that I mark for them on the inside with painter’s tape, making note of any blocking or hurricane bracing that I saw in the IR scans. For the part of the downstairs with stucco on the outside, we’ll have them drill and fill from the inside as we luckily haven’t painted those rooms yet. In total there are maybe ~10 completely empty stud bays, another ~10 with some slumping at the top, and ~5 that don’t look as dense as they could be. There are also a few of those stucco walls outside of rooms that we plan to remodel down to the studs in the near future – I won’t have them touch those rooms, and instead when we later remodel I’ll sacrifice a couple inches of room space and have those contractors fur out those walls in a way that breaks the thermal bridging (Bonfiglioli or Mooney or something like that, depending on what contractor prefers) and gets us a little extra cavity insulation depth.

So far I’m leaning towards the open cell contractor for his proposal and the cost, but I want to make sure the plan is mostly reasonable and to make any necessary updates to his proposal before getting it on the schedule. What do you all think? Thanks in advance!

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. user-2310254 | | #1


    I'll give your post a bump, but I think you are more likely to gather some responses if you create shorter, individual posts.

  2. PAUL KUENN | | #2

    whoa Matt!
    I think you were drinking too much coffee before you began the typing fest. How about a few photos of the house so we know what you are diving into.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |