Insulating and Air-Sealing Balloon-Framed Masonry House
My apologies if this topic has already been covered elsewhere on here and I would be grateful to be pointed to those discussions. Several searches of mine unfortunately did not give me a clear answer.
2-story balloon framed, brick facade, house built in 1900, an hour NE of Toronto, Canada (Climate Zone 6)
My wife and I are currently renovating half of the 2nd floor and are doing a lot of the work ourselves. In those rooms where we are down to the studs and the back side of the original plank sheathing is accessible we want to take the opportunity to air-seal and insulate as best we can.
Aware of the risks when sealing/insulating an an old house (trapping moisture, mould, rot etc.) I did a fair bit of reading (GBA, FHB and some books) and consulted a professional building scientist to come up with what is hopefully a well thought out plan. However, because of the diversity of historic homes and our consultants limited experience with retrofits we are looking for some “GBA-hive-mind-input” so that we don’t overlook anything major and get the details right.
While the partial air-sealing/insulation might not make a big difference in the short term, if/when we renovate other rooms in the house we would then continue the air-barrier and insulation strategy with the opportunity of eventually having an overall tighter and better performing house down the road.
The Exterior Wall:
Here is a list of the layers of the original exterior walls going from the outside to the inside (a rendering showing a cross-section of the wall is attached to this post):
* 4″ thick brick facade
* 3/4″ – 7/8″ air gap
* 1″ thick horizonal plank sheathing
* “true” 2″x4″ studs — stud cavities filled with the following:
** 2″ earth/soil/mud stud-bay cavity filling – REMOVED
** 1″ thick boards in between studs to hold back cavity filling (boards held in place by 1″ x 1″ blocking/furring strips) – REMOVED
** 1″ air gap (in between 1″ x 1″ blocking/furring strips) – REMOVED
* 3/8″ thick lathe – REMOVED
* 1/4″ – 3/8″ plaster – REMOVED
The components marked “REMOVED” will be replaced by strategically (and hopefully correctly) chosen modern materials to allow any moisture in the wall to diffuse either to the inside or to the outside.
The IMPROVED WALL will have the following layers (see also the attached rendering):
* 4″ thick brick facade
* 3/4″ – 7/8″ air gap
* 1″ thick horizonal plank sheathing (gaps “sealed” as well as possible)
* “true” 2″x4″ studs — mineral wool filling the stud bays (approx. R14)
* Intello Plus smart air/vapor barrier
The gaps, cracks, knot-holes etc. in the plank sheathing allow quite a lot of airflow and will likely render the mineral wool insulation fairly useless unless we seal them. So that our plumber could install the bathtub, I started the air sealing and insulation process in that corner by filling the voids in the sheathing as well as the edges of the stud cavities with spray foam, followed by the insulation bats and Intello Plus membrane (see attached images). I’ve not continued with any more sealing of the sheathing as I’ve been wondering whether my approach would be a problem down the road.
1) Are there any major flaws/risks to our air-sealing and insulation retrofit strategy and if so, what are they?
2) It is my understanding that even if the gaps, cracks, knot-holes etc. in the plank sheathing and stud bays are sealed, any moisture in the wall would still be able to diffuse out through the Intello and drywall (to the inside) or planks (to the outside). Is that correct or would I be creating a “mould incubator”?
3) Is the spray foam flexible enough to move with planks? If not, what alternative sealants recommended for an application like this to achieve a good and lasting seal?
Site note: the job site air temperature is currently roughly 3°C – 9°C (37°F – 48°F) and the sheathing itself has dropped below freezing several times this winter, so it would be necessary for an alternative sealant to be able to cure at low temperatures.
4) Will my efforts do a sufficient job to prevent wind-washing of the insulation or does the historic plank sheathing make it a lost cause anyway?
5) If sealing the gaps, cracks, knot-holes etc. in the plank sheathing is not a good strategy, what is? Would I have to line the sheathing side of the stud bay with more Intello Plus or, a 1/2″ or 1″ layer of foam board and seal that to the studs/plates?
6) Am I overthinking this?
Thank you all in advance for your thoughts and input!!
Long live our buildings!
1) Rendering – original wall assembly
2) Rendering – improved/sealed/insulated wall assembly
3) Sheathing that I already sealed with spray foam
4) Detail view of sheathing that I already sealed with spray foam
5) Example of sheathing that I have yet to seal
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