Insulating a Balloon-Framed House
I have read many articles on this website but none that reflects my exact situation I feel… or maybe iIhaven’t read the right one yet?
I’ll keep on reading but your advice would be of great help!
So here it is…
We just bought a house in Sutton, Qc (just north of the Vermont border), in climate zone 6 (for now).
It’s an old 19th century home with balloon frame structure and lath-and-plaster walls.
On the outside of the walls, the studs are covered of 2 crossed layers of hemlock planks, then clapboard siding and finally a vinyl covering. No air gap or weather barrier behind the clapboard.
We plan on leaving the vinyl for now and focus on insulating from the interior…
but since our budget is limited, we planned on renovating the upper floor first and doing the rest in a year or two.
We demolished all lath and plaster on walls and ceiling of the second floor and got rid of the old loose wool insulation in the attic. We now see the interior side of the hemlock planks of the roof but the walls have a second layer of lath-and-plaster in between the studs (probably to create a double air gap “insulation”).
We plan on removing this additional lath-and-plaster layer since it is falling apart on certain walls.
(picture of the inside of exterior walls attached)
We then plan on building a new stud wall on the inside, with a 1/2″ gap between the old and the new studs in order to reduce thermal bridging. This new cavity would then be filled with cellulose. My main concern now (as evevrybody who is insulating an old house) is condensation inside the cavity.
My contractor suggests to install a smart vapor barrier on the inside and fill the wall cavity with cellulose. Though i like the simplicity of it, would that be enough to allow the humidity to dry to the inside since there is no weather barrier on the outside and no air gap between the hemlock planks and the clapboard?
I was thinking of using a variation of the method described in this article: https://www.greenbuildingadvisor.com/article/insulating-walls-in-an-old-house-with-no-sheathing
By recreating the existing air chamber behind the hemlock planks with 3/4″ spacers nailed to the studs and then fasten a layer of insul sheathing to the spacers. We would do this ourselves because cutting and fitting and sealing the insul sheathing boards inside the stud bays will be time consuming.
The contractor would then insulate the remaining “double stud” wall cavity with cellulose and finally add a layer of EPS rigid foam with aluminum foil vapor barrier on the inside. A double layer of crossed furring strips on the warm side of the aluminum foil would then allow the electrician and plumber to do their job without having to cut any holes in the vapor barrier.
This “new” air gap behind the hemlock planks would then allow the whole outside cladding assembly to dry if necessary, and the insul sheathing would now serve as “weather barrier” if humidity gets in from the outside and also allow the insulated cavity to dry to the outside.
Same approach would be used on the first floor in a year or two when we renovate the rest of the house.
So am I being too cautious here by recreating this air gap?
Will the Smart Vapor Barrier be enough to allow condensation to dry on the inside?
(Wall assembly options attached)
Any other wall composition idea would be appreciated but what’s for sure is that we will not insulate from the outside for now and we do not want to use spray foam and as little rigid foam as possible.
Thank you in advance for your help on this!
Felix & Melody
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