Insulating kneewalls in a 1910 balloon framed Cape
Let me start off by saying that if my employer looked at my browser history and saw how many hours I’ve spent researching this predicament I’d probably be fired. As an avid DIY’er in a single income house I’m really hoping to take care of, or at least alleviate the summer time heat problem in my upstairs bedroom without calling in the pros.
– 1910 construction in St. Louis, MO
– Zone 4, but just south of Zone 5.
– 10/12 hip roof with 2 full window dormers.
– Balloon framing. 75% of the exterior walls are insulated with batts, none of which have insulation extending into the top of the stud cavity in the attic space.
– 6′ large knee walls on both sides of the home that is intended to be storage space. 3′ sloped ceilings before flat ceiling.
– All of the band joists have fiberglass bat insulation, about half of them have wood blocking as well, but are not air sealed.
– There is HVAC upstairs.
I bought the house in August of 2018. The upstairs was hotter than Haiti until until October-ish. The upstairs/roof/attic was completely sealed aside from a white 750 slant back installed towards the bottom of the roof on the attic side of 1 knee wall. There was R11 and R19 fiberglass batts installed on the roof deck, but with almost every rafter exceeding 24″ OC, the guy essentially stapled the batts to the roof deck. This significantly compressed them and left a 1″ uninsulated gap on each side of the rafter cavities. The dormers also had the same insulation stapled to the roof decks.
Based on research and advice from others, I removed as much of the fiberglass batts as possible from the roof deck, fully vented the soffits on the two long sides of the home, and added 2 turbine vents near the roof ridge. While installing the roof vents I was able to pull off the roof deck stapled batts that were previously unaccessible and lay them on top of the flat ceiling. I was also able to ensure a clear path from the soffits to the roof ridge, and laid radiant barrier on top of the flat ceiling insulation.
Fast forward to this week. I have since face stapled a perforated radiant barrier to the rafters from the top plate/soffit to the top of the knee wall and added R10 foam board to the knee walls. I have not air sealed the foam board yet since I wanted to test its performance before making it more a “permanent” install. I’m starting to think I should’ve installed the foam board on the rafters.
Today was mostly sunny with a high ambient temp of 80ish. At 7pm my upstairs was 87 degrees. The walls, sloped ceiling, and flat ceiling were all low to mid 80’s, but I did find a few hot spots on the top of the walls and sloped ceiling that were pushing mid 90s.
I have started pulling up the attic floor so I can add blocking and air seal the floor joists under the knee wall, but decided to seek more advice before trying anything else.
Based on what I’ve described, does anyone have any recommendations specific to balloon framing/cape cod? I’m almost inclined to blow both the knee walls chock-full of cellulose and drywall over the access doors.
I do realize I’ll probably have to sacrifice some of the 2″ foam that I currently have on the knee walls, but at least I can use that for other insulation purposes.
Sorry for the long winded post and any help appreciated.
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