Rigid foam insulation
Can I use rigid foam insulation to insulate the interior walls?
The house has block walls that the mortar in places are uneven on the interior. There is brick on the exterior. The wood frame on the interior has cedar wood about 1 x 3 inches I am guessing. I live in New York City. It is a town house connected to a row of homes. At this time I am not able to insulated from the outside.
If we can use rigid foam insulation, what else would I need to do besides framing the foam in between the wood studs?
Also under the window there is at least a 3″ gap between the block and the bottom of the window sill. What do you suggest to fill in that gap if it needs to be filled in?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
> framing the foam in between the wood studs?
Yes, you can use foam on the interior side. Put it over the studs (not between them) and it will perform better. Also consider "flash-n-batt".
https://www.greenbuildingadvisor.com/article/why-flash-and-batt-makes-sense
Esther,
You can fill in the gap between the concrete block wall and your rough window sill with rectangles of rigid foam, sealed at the perimeter with canned spray foam. But if you are asking questions like that, I'm wondering if you are in over your head -- whether you might need to hire a contractor.
One question to consider, for example: Do your windows have proper flashing to protect their rough openings? Have you addressed the possibility of bulk water entry into your walls?
Hi All
Thank you for your response. I read the articles. I definately do not want freeze/thaw damage. I enclosed some pictures of the wall and under the window sill. I hear what you are saying. There is not much space. We was going to try the 1/2' rigid foam. Jon suggested covering the wood studs instead of going in between. I was trying to find the right way to insulate the interior walls just the front and back of the house. The other walls are attached unless you suggest in your experience to do the other walls as well. I reached out because I wanted to do it right.
I second Martin on calling for an experienced contractor. Retrofitting insulation onto masonry walls can be a very delicate operation, and if done poorly can lead to freeze/thaw damage to the structure. GBA had Joe Lstiburek on a podcast to talk about it a few years ago: https://www.greenbuildingadvisor.com/article/insulation-retrofits-on-old-masonry-buildings-building-science-podcast
This article also provides an overview of some of the issues: https://www.buildingscience.com/documents/digests/bsd-114-interior-insulation-retrofits-of-load-bearing-masonry-walls-in-cold-climates
Hi All
Thank you for your response. I read the articles. I definately do not want freeze/thaw damage. I enclosed some pictures of the wall and under the window sill. I hear what you are saying. There is not much space. We was going to try the 1/2' rigid foam. Jon suggested covering the wood studs instead of going in between. I was trying to find the right way to insulate the interior walls just the front and back of the house. The other walls are attached unless you suggest in your experience to do the other walls as well. I reached out because I wanted to do it right.
Esther,
Doing this properly without the potential for damage requires more information about the assembly, specifically how it handles bulk water. Relevant information includes:
-Is there a gap between the brick and the block wall? If so, how large?
-Does that gap have openings in the top and bottom to allow ventilation? Is it mostly unobstructed by things like brick mortar?
-How old are the cement blocks and bricks? Are they of good quality?
-Is there any sign of freeze/thaw damage anywhere in the assembly already?
-Is there any sort of WRB on the exterior surface of the blocks?
-Are the windows and other openings flashed properly? Where does the flashing direct the water?
-Are there overhangs, parapets, and drip edges protecting vulnerable areas from water penetration?
And so much more. There is no good one-size-fits-all approach for these old masonry buildings. Understanding the moisture risks of these assemblies and formulating effective insulation strategies involves "experience and judgment", as Joe Lstiburek puts it.
All that said, 1/2 inch of foam is not worth the effort in any circumstance, especially when thermally bridged. Any insulation strategy should also include strategies for insulating areas between floors as well, and any basement requires special attention. Spray foam is commonly used for these purposes, usually 2" of closed cell. You'll need a contractor for that.
The good news is that there is probably a gap between the brick and the blocks, and with any luck it is large enough and detailed to provide ventilation and drying. That will make things easier, and might give you some more wiggle room. How much wiggle room, I don't know -- this is not my specialty, I'm just some guy on the internet. The best thing to do is call up some contractors who specialize in this thing and get some quotes. Perhaps NYC or the state has an energy retrofit program that might be able to help, and provide subsidies to boot.
Thank you