I am planning on insulating a 100+ year old brick house located in Ontario Canada. Existing Wall Construction: brick, 1" air space, air barrier / waterproof membrane, wood sheathing, 2x4 (actual) wood studs, lathe and plaster wall finish. I think the best way to do this would be to remove the existing lathe and plaster, then install batt insulation between the existing studs, complete with a poly vapour barrier, and then drywall. What are everyone's thoughts? Thanks,

If the plaster is in reasonable shape it's better to install blown dense-packed cellulose drilling from the interior. Since it's balloon framed you'll have to block the floor joists near the wall, which is typically done by drilling a hole in the ceiling near the wall, inserting a woven burlap or woven plastic bag (of the type used for large animal feed), and dense-packing the bag in place to form a plug. You'll also have to retrofit air barriers at the plate-less top of the stud bay, and often at the bottom at the foundation sill.

Most 100 year old plaster has multiple layers of oil paints, with a vapor retardency sufficient to meet the Canadian code definitions, but if your inspector balks, painting over it with "vapor barrier latex" guarantees it.

Most 100 year old houses were built with full-dimension lumber, and not always on standard spacings. Either way, there are no batts designed for a perfect fit on either width nor depth. That makes installing batts adequately a much more time consuming and error-fraught solution. Blown fiberglass would work, and be somewhat higher-R than blown cellulose, but cellulose offers significant hygric buffering- it shares any humidity load from incidental air leaks or vapor diffusion with the structural wood, which limits the moisture content of the structural wood. It's borate fire retardernts are also anti-fungal anti-mold, which protects on yet another level. Insist on "borate only, sulfate-free" grades of cellulose, which is a miniscule cost-adder, but limits the potential damage should it ever get wet.

Before insulating any 100 year old framed building it's important to verify the presence & quality of the window & door flashings. An empty balloon frame drys quickly after incidental bulk wetting, but once those cavities are full of insulation it takes orders of magnitude more time. If there are roof overhangs of a foot or more per story of building height direct bulk wetting is much less likely and you may be able to get away without window flashing, but in high wind areas maybe not.

Dana you are a champion for knowing all this. It's insane!

Posted By James02 on 08 Dec 2015 08:15 PM
Dana you are a champion for knowing all this. It's insane!

Naw, it's easy- I just make it all up as I go along...

...and sometimes get lucky when it happens to be right! :-)