I'm trying to decide how to insulate the 'triangles' on the sides of my finished attic. The house is 100yrs old and is made of ceramic tile covered with brick on the outside. The tiles are covered at the top with some plywood but are likely still acting like chimneys. My current attic insulation is about 2" of cotton batts loosely placed between the roof trusses (I.e. Nothing). We live in Illinois, and like many other places, winter was very cold this year. The space I'm trying to insulate is at the edge of the attic behind a knee wall and out to the edge of the house walls. I've read that foam would seal against all air flow but that it's expensive. Alternatively I could blow cellulose into these spaces but I'm worried that it would settle and that it wouldn't stay up against the roof. Have any of you used the DIY foam kits from the box stores? With thanks in advance for your advice.