I need help insulating a kneewall
I recently had an energy audit done, and, not surprisingly, big issues were found with the knee walls on the second floor. This is a “contemporary” Cape in Massachusetts.
I’m in the middle of rectifying the problems. Here is a description of the issues.
The knee walls themselves have zero insulation, except for one room where they have R19 in the wall. The floor of the knee wall space has what looks like R13, except for this one room where it looks like R30. There are no ventilation baffles on the sloped ceilings at all. There are soffit vents, and a ridge vent in the top attic, as well as gable vents in the top attic with thermostatically controlled fans. No gable vents in the knee wall space. The rafters are 2 x 8, 16″ on center.
The sloped ceiling on the north side has R19 fiberglass. Half of this knee wall is 7 feet tall, and the rest is about 3 feet tall. There is a skylight in the sloped ceiling. For the 7′ wall part I basically have full access to the sloped ceiling, but for the rest only a few feet. This rest makes up cathedral ceiling in the house.
The sloped ceiling on the south side has what looks like R11 on top of R13. This wall is only 21″ tall, and there is a dormer, as well as a skylight in the sloped ceiling. I have access to only a few feet of the ceiling, and the rest is cathedral in the house.
The thermal boundary is clearly ambiguous.
What’s the best way to go about solving this?
How is this for a plan? (I realize this continues the thermal ambiguity.)
1) insulate the knee walls themselves with R13 covered with radiant barrier, and air seal under the knee wall
2) put R30 in the floor of the knee wall attic space
3) leave the sloped ceiling insulation and install ventilation baffles behind it as best I can. I’m not sure I can get the baffles all the way up to upper attic because of the cathedral part of the house. On the 7′ part of the knee wall I definitely can, though.
The thermal boundary is already ambiguous because there is insulation on the sloped ceiling, floor, and knee wall.
Or is it better to try to get closed cell foam on the sloped ceiling? Can I really get the desired R-value with 2 x 8’s all the way up through the cathedral (and skylights)?
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