Insulating walls on a brick house

[brian89gp]

I have a 2 story solid brick house, 3 wythe (3 brick thick), with plaster directly on brick on the interior. Heat loss and gain through the walls is significant once they either heat up in the summer or cool down in the winter just due to the thermal mass. HVAC-Calc shows a drop from 160k BTU to 95k BTU heating and from 7 tons to 4.5 tons cooling with insulating the walls (160k and 7 tons is with everything sealed up and the attic already insulated)

I was planning on building out a metal stud 2x4 wall on the inside of the brick walls leaving 1/2" gap between the studs and the brick then spray foaming the whole thing including the 1/2" gap with open cell foam. Metal studs because my ceilings are 10' and straight 2x4 of that length are hard to find and open cell foam vs closed cell because open cell is vapor permeable so it would not trap moisture in the wall. The foam directly on brick would not allow a cold surface for condensation to happen, a problem with batt or cellulose insulation.

Thoughts/opinions? Am I better off leaving well enough alone for the sake of the brick? It is the old soft brick with lime mortar that is sensitive to moisture and freezing.

 

[G-rott]

My thoughts, first open cell foam is the right product for this situation. I would look for 2x3 studs to minimize thermal bridging, leaving more space behind the steel framing. Going through this much trouble to insulate correctly be sure to address rim joist and sill plates too.

I don't see how this could negatively effect the brick, it will be subject to fewer freeze thaw cycles as it will be outside the insulated space.

What did you do to insulate the attic?

 

[brian89gp]

Its an old house, built in 1890, so a lot of things were built differently back then.

I would look for 2x3 studs to minimize thermal bridging, leaving more space behind the steel framing

I'll try and find some 2x3 metal studs, good idea.

Going through this much trouble to insulate correctly be sure to address rim joist and sill plates too.

No sill plates and no rim joists. The wood floor joists sit in pockets in the brick wall, I haven't decided how I am going to handle it but I am just considering leaving that section un-insulated so that the ends of the floor joists don't rot out.

I don't see how this could negatively effect the brick, it will be subject to fewer freeze thaw cycles as it will be outside the insulated space.

I just worry alot because this old brick is really soft, it doesn't take much to cause damage. Something as simple as repointing with cement based mortar can destroy a wall in a decade. My thinking was that I am no longer pumping heat into it from the inside it might be subject to more freeze thaw cycles as the outside temp here normally swings above and below freezing all winter.

What did you do to insulate the attic?

The attic, otherwise known as the 3rd floor (12/12 slope roof with the peak about 15' above the attic floor), has R30 fiberglass batts in the floor joist cavities and I am in the process of putting up 4" of foam board on the inside of the roof. 2" is inset inbetween the rafters and then 2" more on the inside face, this gives continous R10 with R20 inbetween the rafters while still alowing 4" behind the insulation for roof venting. Its unfinished now but I wanted to leave the option open in the future to finish it off since it is 1200sq/ft of very usable space.

 

[semipro]

OP, ever considering building exterior walls with thermal insulation and air/vapor control outside the brick?
Sounds crazy I know but many deep energy retrofits include building out instead of in.
Thermal mass on the interior is a good thing.
If the brick is old and crumbling continued exterior exposure would only make this worse.

 

[G-rott]

Good thought...I like the thermal mass on the warm side of the wall.