Hi- I'm redoing an upstairs room in my 1950's brick home.  the existing interior walls are rock lath attached directly to the brick (w/ some type of black coating on it) via 3/4" wood strips.  Since the room never had insulation, I though this would be a good time to do so, though it would require removal of the existing walls and starting from scratch (which I'm willing to do if it's worth the effort).  I'm trying not to make the room much smaller, so my thought is to frame out the walls with 2x3's and then place R??? batts in between each stud.

Is this the proper way to insulate or is there a better method?  I've been reading about foam board insulation, but the R value seems low.  This is my first home, so looking for any guidance from the experts.  Thanks!

Brick stores substantial amounts of dew/rain water, and releases it to the interior as water vapor when the sun hits it, or via capillary draw from matetials in direct contact with it. Batts in a studwall as your solution could be a disaster, since high moisture drives from the brick will likely create mold conditions on the studs. Any insulation want's to be perfectly air-tight, and/or all of wood in the assembly needs to be on the conditioned-space side. You also need to preserve at least a 3/8" ventilation cavity between the brick and the interior assembly. For about the space than a 2x3" studwall you can use dual-layers of 1" XPS foam sheathing to get there, and end up with 1.5-2x the true R value.

Brick | spacer for mainainting the cavity | 1" XPS + 1" XPS | wood furring | 1/2" gypsum

The cavity can be as narrow as 3/8", but the spacers need to be moisture tolerant (plasic, ceramic, metal, whatever. Cement-board or PVC furring works.) The first layer of XPS can be cut to fit and held in place with blobs of foam-board construction adhesive (which uses solvents that won't eat into the foam). Use duct mastic, FSK tape, or foam adhesive to air-seal the seams, and stagger the seams of the second layer by at least a foot. Seal the interior layer of foam similarly, and use 1-part foam to air-seal the edges. Long-screw the furring into the masonry, and hang the gypsum on the furring. To meet fire code the gypsum needs to be 1/2" minimum (as a thermal barrier against ignition for the foam.) Interior wall finishes should be at least semi-permeable to water vapor or even through 2" of foam you could end up with mold on the furring. (No vinyl or foil wall paper. Standard latex paints are fine.)

With no studs thermally bridging the insulation layer, with XPS you'll end up at a true R9.5- R10 (whereas R7-R8 batts in a 16" o.c. 2x3 studwall perform more like R5-R6, if installed PERFECTLY, with no gaps/compressions.) If you need to go higher, a dual 1.5" (3" total) of foil-faced poly isocyanurate with FSK-taped seams & foamed edges can get you up to ~ R20 for an additional inch of depth over the XPS solution.

Hi, I have a house built in 1956 with the same walls as nyjets77 and I am starting a major reno. My plan is to build 2x4 wood stud interior walls butted up to the existing drywall with spray foam insulation applied directly to the existing drywall/plaster. This will leave the original cavity to breath but my concern is will there be a water vapour/condensation issue with the old drywall? I would like to avoid removing all the old drywall if possible. Other parts of the reno include new windows and complete roof replacement, new furnace and complete basement build out. Thanks.

I should add this is located in Scarborough, Toronto and is zone 7A so we do experieince both ends of the temperature scale from around -20F in winter to 90F in summer.

Scarborough/Toronto is actually more like a zone 6A climate (the warm edge of 6A at that):

http://www.greenbuildingadvisor.com/sites/default/files/Climate%20Zone%20map%20including%20Canada.jpg

It's better to gut the existing wall and take a hard look at what's there before proceeding than to just build over it. There could be issues with the brick to fix before moving forward, and the exact materials of the furring & lath may be a problem, especially if the masonry cavity is not vented to the exterior with weep holes near the bottom and vents near the top.

With as little as 1/2" of air gap between the brick and 1.5" of foil-faced polyisocyanurate or 2" of EPS on the exterior side of the new studwall would allow you to skip the interior vapor barriers with a fiber-insulated studwall, since the interface between the rigid foam and the fiber insulation in the studwalls would average above the dew point of the interior air in winter. If you're not going to gut the existing wallboard, put 1.5" polyiso or 2" EPS snug up against the old studwall. But don't just putting the new studwall up against the old stuff without the foam is riskier, and it would be well below IRC 2012 code-min for zone 6A.

While 3.5" of closed cell polyurethane between studs comes close to meeting IRC code for center-cavity R, it dramatically underperforms code on a U-factor basis due to the high thermal bridging of the shallow 3.5" framing. It's truly a waste of foam, and it carries a significant envirnmental hit due to the blowing agents used. (XPS has similar issues, dramatically worse than EPS, polyisocynaurate, or open cell spray foam.)

If you're re-roofing it may be necessary to install rigid foam above the roof deck with more insulation between the rafters to hit the IRC prescriptive R49 for zone 6A. In zone 6 as long as at least 50% of the total R is on the exterior of the roof deck, the roof deck is well protected from interior side moisture drives. If the rafters are milled 2x6s, R23 rock wool with 4-5" of polyiso above the roof deck works great. The polyiso can be done as 2-3" of fiber or foil faced goods with a top layer of nailbase panel (where one facer of the polyiso is OSB), through screwed to the original roof deck per the manufacturers' fastener type & spacing specifications.

On the basement build out, again, put 2" of EPS or 1.5" of polyiso against the foundation before installing the studwall, and skip the interior vapor barriers. Put an inch of EPS (but not polyiso) under the bottom plate of the studwall as a capillary and thermal break to keep moisture from wicking up from the slab into the wood, or adsorbing from summertime humid ventilation air.

If the local building inspector insists on seeing vapor barriers despite the exterior side foam, use 2-mil nylon (eg Certainteed MemBrain) rather than 4 - 6 mil polyethylene. When the proximate air to the nylon is below 40% relative humidity it meets Canadian code definition for a minimal vapor barrier, but if moisture ever NEEDs to get out and the air in the cavity is north of 60% RH, it becomes more vapor open, and allows the moisture to dry toward the interior. With a reservoir cladding such as brick on the exterior this is a critical difference. There are many brick homes in Ontario with insulated studwall interiors that have summertime condensation problems inside the walls due to polyethylene vapor barriers (especially but not exclusively in homes that are air conditioned.)

Hi Dana1, thanks for responding so quickly. I agree Toronto is not extremely cold, especially this year, but we do get a fair variety in temperatures. I got the 7A from a different table, apparently it was for plants. Anyway I agree with demolishing the existing 1st floor interior walls but I'm torn and didn't really want to. I am never a fan of taking short cuts and I used this post to basically re-inforce what I already thought. I have had other people suggest that if I were to seal and insulate the attic really well I shouldn't need to demo the walls and rebuild for insulation purposes. I don't agree with that but it has been said. The thing is this is my Mom's house and the reno is to bring it up to full value and sell it. I will not do anything that would pass a future problem on to anyone else. I have been out of residential renovations for many years now and have not really kept up with the building code, the insulation requirements have changed drastically. I do agree with the insulation and sealing everything air tight but I'm also trying to balance a good job with a budget. I would use either your option 1 or 2 depending on the building inspectors point of view on what he would pass. 2x6 studding is an option but is kind of intrusive in a small bungalow (750 sq ft). There is a possibility I will leave the walls as is. For the roof insulation I am considering a radiant barrier using 4" Silver Glow and blowing insulation on top of the ceiling joist, again the inspectors opinion being vital. I will build the basement as you have specified and hopefully the inspector agress the wall does not need any further vapour barrier. Thanks for the 2 mil polyethelene suggestion if the inspector insists, I probably would have used 6 mil. I am not a fan of vapour barrier in contact with drywall but if the inspector insists theres not much I can do about it. Thanks again for your very detailed response, I really do appreciate it.

That's 2mil nylon vapor retarder, and definitely NOT polyethylene. Nylon's vapor permeability changes with the humidity of the air next to it, and can behave something like a relief valve- it can't trap moisture, whereas polyethylene's vapor permeance isn't affected nearly as much, and will trap moisture, even at 2 mils.

In your climate a simple radiant barrier has vanishingly small value, but SliverGlo is foil-faced graphite loaded EPS, which could be useful if properly applied. It needs an air space between the shiny facers and the adjacent layers for the facers to add any benefit, but in combination with fiber insulation there can't be an air-gap between the fiber and the panel. If the panel is on the exterior side of the foam/fiber sandwich the panel has to be at least 50% of the total R, so it gets a bit complicated. It's not clear to me where/how you were planning to install the panels relative to the blown insulation.

IRC 2012 or newer code min walls would be the equivalent of R20 continuous insulation. The thinnest wall that would deliver that with reasonable moisture handling would be 3" foil faced polyiso, with a 1/2" cavity between the polyiso and brick, with no interior studwall, but that makes electrical routing difficult.