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Benefit of lath

Currently my husband and I are demolishing a 100 years old brick house to install insulation. So far we chipped off plaster and there are laths an inch off from the exterior wall. I am thinking of installing insulation on top of the laths in order to minimize garbage. Does having the laths benefit of keeping the mold free? Or just wasting space? If I decide to remove the laths, can I put insulation on the exterior brick wall directly? Please advice.

Re: Benefit of lath

It sounds to me like what you're calling lath is what the builder used as exterior sheathing... you do not want anything up against the brick... it needs an airspace because water/condensation can build up behind the wall.

Re: Benefit of lath

I think my original explanation was poor and might have caused a misunderstanding. Allow me to explain again.

I need to make an insulation decision on a 100 year-old home that has double brick exterior walls. I need to insulate the exterior walls.

Starting from the outside, working in: 1) double brick exterior walls with a 1" air space between the 2 brick walls, then thin wooden studs nailed vertically into the interior brick, with the horizontal lath nailed onto those studs , and then the usual plaster on the laths.

Before gutting the inside completely, I would like to know if I should keep the lath as it is, and add 2x4 framing which will back onto this lath. (The lathe would hold the new insulation from the brick by 3/4" or so) Then I'd put Roxul into the new 2x4 stud wall, and vapour barrier and drywall the new wall in today's standard method. I think that doing it this way, the 1" gap that the between the double brick exterior walls and the lath that I leave in-place, will allow the brick to breathe and remain mold-free.

I acknowledge that this will shrink the room by the width of the new 2x4 studding and drywall surface.

Anyone have any experience with this, or comments about my proposal?


Re: Benefit of lath

I don't see a need for the lath if they (the lath) are already firred out with the vertical studs. Even 1/2-3/8ths is enough for air movement, IF there is any air movement. If you have a vapor barrier and such, the wall won't be breathing much anyway, but it's better than no space.

You're probably using foam board insulation, which is rigid anyway, meaning that you'd get the air space. If you are using fiberglass or other fiber insulation, I think leaving the lath is a good idea.

Remember though, for all that work, you will still only have your 4" wells to insulate, so not a lot. Id stay with foam board insulation to get the highest R out of the space. Get the stuff with the reflective side to kick back IR into the living space. I'm sure you're on top of this though. With foam board, you can get away with less air movement because it's less likely to compress and even a small amount will let the brick breath because it has a small gap in between the brick layers anyway.

Personally I'd remove the lath because it's going to be a hassle to deal with while you try to plumb the studs and build out. It's going to crack and shift and generally get in the way. If you tore out the plaster, what's a few cubic yards of lath?

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