I am looking for some advice on insulating my knee wall space. This will be out third winter in this house. The past two winters we’ve notices quite a bit of ice damns and parts of the ceiling around the knee walls on the first floor are quite drafty. Currently there are baffles in-between each rafter with batt insulation over the baffles stapled to the rafters, the knee wall floor also has batt insulation and the interior wall is insulated with batts. There are heat pipes in the space feeding the second floor bedrooms so I imagine we’re loosing quite a bit of heat to this space making the insulation on the interior walls unnecessary and maybe even having a negative impact.
I currently only have access to one side, when I’m ready to start working I will be cutting access holes inside of a closet to get into the second knee wall area as well as the space above the ceiling. So my plan is to bring the knee wall space into the conditioned envelope since the heat pipes are there and we could use the space for storage. My question is should I leave the batt insulation between the rafters and put rigid foam over top of it, as far as I can tell from the research I’ve done it doesn’t look like we can get enough R-value with just the rigid foam for the Upstate New York winters. We don’t have a huge budget for the project but I want to get something done for this winter so are there any reasons against putting 2" foam up and adding another layer of ridged foam on top of that in a year or two. Also any suggestions on products would be appreciated.
Thanks for the response Marcell. I did see that graphic during my internet travels. I guess my question boils down to whether to leave the batt insulation under the rigid foam, that’s the piece of info that cannot find. I didn’t find a forum where a couple people were arguing about it but neither really had any substance to their argument.
I don’t know if you know this or not, but the #1 reason you get ice damming is due to conditioned (warm) air infiltration, not lack of insulation. You can have R60 insulation… and still have plenty of ice damming if you have poorly sealed attic from the rest of the house space.
as far as the foam, what type is it?
My opinion would be to climatize the knee space and install the foam in the roof rafters with an air space to allow the ventilation from the soffit to the ridge.
I would also install batt insulation to fill the remainder of the space to maximize your R factor.
I have done that before in a new build and has proven well up here in this area.