Insulating Out Side Walls?
we’re renovating a room in the rear of our house (south facing) and redoing all the walls, windows, ceiling etc. Just wondering about what we should do to insulate between the new sheetrocked wall and the outside brick? There’s just the standard plaster/lathe there now. could i spray foam that or will that cause some…
we’re renovating a room in the rear of our house (south facing) and redoing all the walls, windows, ceiling etc. Just wondering about what we should do to insulate between the new sheetrocked wall and the outside brick? There’s just the standard plaster/lathe there now. could i spray foam that or will that cause some kind of moisture problem (or other problems)?
thank you all for the great responses! the brick is in great shape all around our building…but i think i’ll go with ‘young archi’ advice and do a little rigid in as
well…doesnt seem like it would be too much more of a hassle.
This is actually a really good question that is relevant to any old brownstone or masonry building renovation.
1. Vapor difussion is always an issue but i don’t see any issue with this assembly, from a vapor perspective.
2. The larger issue is that you are changing the thermal gradient within the masonry. Here’s what I mean:
Insulating the interior side of the wall decreases the overall temperature of the wall (less heat is escaping the building and warming the bricks). Before you insulated, the exterior wythe of brick (the best brick in the wall) was subject to freeze/thaw cycle. Now, depending on amount of insulation, you’ve subjected the entire wall (and the weaker bricks) to freeze/thaw.
So, the question becomes, what shape is the masonry wall in to begin with?
I know my company has been retrofitting the interior of existing masonry walls for years and never had any problems, yet other professionals swear this can destroy the masonry – it really just comes down to the quality of the existing masonry.
3. If you’re going to insulate, take Emperiums advice but take it a step further: Put 1″ polyiso rigid insulation against the masonry wall. Face the foil face in to the building, tape the seams. Then mount the stud wall and spray foam on the inside of this, and finally gyp board.
This is an excellent retrofit assembly and can add up to R27 for a 3.5″ stud or R21 for a 2.5″ stud.
Best of luck!
you can also consider the more “natural” cellulose alternative (no chemicals in your house). it can be blown wet and will fill the cavity like the foam does but it’s all recycled paper… R is around 3.5 per inch. see video of installation here: http://www.youtube.com/watch?v=FOFoKSnKvZY
closed cell spray foam is expensive, but is indeed airtight and has a great r-value (5+ per inch). If you can afford it, go for it. But do make sure non of your metal studs touch the brick wall, if they do, these thermal break will diminish you r-value drastically and you might as well have insulated with batts (not really, since you are still airtight, but you did throw hald you r-value out the window)
Closed cell spray foam is the way to go if you truly want to seal the wall. You use less space, seal it tight and get a good R-value. It is more expensive. You could do a composite of 1″ closed cell and batt insulation over that.
Since the walls will be open, why not use rolls of fiber glass with a vapor barrier?
you do have to think about moisture when you insulate, but i would love to hear from an hvac person about this one myself.
with no air ducting or air exchanger, i have been wondering if insulating outside walls will make the house into a co2 coffin. as it stands already its quite hard for me to get rid of errant odors and i have no insulation except the roof. ironically that is the problem floor.
hopefully someone knowledgeable can chime in.
I specified sprayed foam insulation in a warehouse conversion to condominiums in Manhattan: we used between 4″ and 6″ of closed cell sprayed foam between the brick and the interior sheet rock, for a minimum r-value of 19 (the 2″ difference is because of the irregularity of the brick wall).
The sprayed foam insulation has the advantage of creating a continuous vapor barrier since it creates an air tight installation. Therefore there is little chance that moisture can migrate from the interior warm space of the house and condense within the insulated wall. Additionally, if you are using metal studs, the sprayed foam gives the added advantage of filling gaps between the studs and the brick wall, eliminating thermal breaks for loss of heat through the wall.
I believe that this is the best option for insulating masonry walls. In addition to the high r-value, which is measurable, sprayed foam gives the immeasurable added advantage of filling all the gaps, resulting in much less heat loss than with batt insulation.
Thomas Barry, RA, LEED AP
http://www.opera-studio.com