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Peter Shepherd 09-15-2009 10:17 AM

Insulating brick above & close to grade
I'm renovating a second floor bathroom in our 100 year old solid brick semi, and would like to insulate the inside of the wall and the joist bays in the floor. I've heard different methods recommended by CMHC (Canada Mortgage and Housing Canada) and elsewhere, but have slight concern about freeze/thaw of old brick wall - in our case sand-blasted, which doubles the surface area & absorbency. I like the idea of leaving the space between strapping to allow heat to penetrate from below, but then add 2" of extruded styrofoam over the strapping, as one green architect did recommend leaving the strapping space empty to help dry out brick wall with fugitive heat. The existing assembly had no vapour (unless 1985 paint job was oil) or air-barriers, just 1/2" or 3/4" expanded styrofoam flopping around between strapping.

Typically for insulating brick I put 15 lb felt or Typar against the brick & build in a 2 x 4 steel stud wall offset inwards to allow for 5 1/2" (R-22 of Roxul). I suppose the steel stud may be slightly susceptible to condensation on outer edge, as there would only be double-brick, then 2" of Roxul (R 8) before outer edge of Roxul, but I prefer working with steel.

As for insulating headers, our Eco-energy Ener-guide report gives a mixed message on insulating between basement joists set in masonry pockets, saying that they'll give you a rebate if you do insulate, but to beware of air-sealing and insulating too much close to grade, as joists may rot out with rising damp from (in our case) old coursed rubble foundation (ours is damp-proofed inside & out, & exulated at basement level) or perhaps with driving rains through brick from outside. The basement joists are18 - 24" above grade, & moisture above interior Delta MS membrane is readily visible just at grade but not much above that. I think that one part of the Ontario Building Code says its okay above grade (as does CMHC’s “Keeping the Heat In”), but doesn't say anything about insulating headers close to grade in masonry pockets. OBC 1997 (1) stipulate leaving 1/2" airspace around joists "at or below ground level" and (2) "not blocked by insulation, v.barriers or air-tight materials".. It would be good to have more clarity on what constitutes a susceptible foundation/joist intersection or wall over-all.

One friend has spalling brick at grade after her 100 year old solid brick basement was well-insulated from inside (don't know how close to grade basement joists are, though there were 6 steps up to porch at front so I suspect it they are well elevated), though everyone else (home inspection teachers) have said to go ahead & not worry about brick if insulating above grade. The wall of our second floor bathroom is far from the 6" perimeter of the brick wall at top, bottom & outer edges that receive the strongest driving rains, and the adjacent house is 7' away, so would stop some rain exposure.

Any advice or experience with insulating brick either above grade or close to it?

stuart45 09-16-2009 06:41 AM

If you use internal insulation on walls with old, soft porous bricks there will always be a chance of the brickwork spalling, depending on your climate. The chances are increased if the brickwork is repointed with a strong cement mortar.

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