What is best practice for insulating the typical story and a half, where the second floor walls that parallel the roof ridge are built maybe 3 or 4 feet inboard from the exterior walls on the main floor below?
In my case we’ve got to build a short pony wall of about 3 feet in height to get its top plate up to where the rafters will bear.
Do we insulate the 2×4 wall at all, if we are insulating the pony wall and the rafter cavities above the “attic?”
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Replies
you'll probably need to clarrify, are you building 2 short walls? Typically only one wall is required to finish the bottom wall of the room and take to reduce the rafter span. Is the rafter cavity spray foamed, or how is it vented. You need to decide what you want conditioned draw the line in the sand and start v.b. and insulating from there ..
So what you have is a classical half-story, possibly an attic conversion. It has a cathedral ceiling of sorts, and you have kneewalls several feet inboard of the lower floor's exterior walls.
The hard part is insulating the "cathedral ceiling". Once that's done you can either continue that insulation down to the eave, effectively insulating the area behind the kneewall, or you can stop the insulation at the kneewall and then insulate the kneewall and the bit of the lower floor's ceiling that's between the kneewall and the exterior wall.
Which way you do it has to do with several factors: How is the roof being ventilated? Will there be storage access through the kneewall? Is this retrofit or new work?
"The hard part is insulating the "cathedral ceiling". Once that's done you can either continue that insulation down to the eave, effectively insulating the area behind the kneewall, or you can stop the insulation at the kneewall and then insulate the kneewall and the bit of the lower floor's ceiling that's between the kneewall and the exterior wall."That's how both the houses I've owned were done, and IMHO it just plain stinks. Hard to detail, and leaky.
OTOH, it's pretty hard to get the r-value just insulating typical rafter spaces, and even if you do, preventing leakage at the eaves would be very hard.
Full foam in the rafter bays and a cold roof above.......
I have a bunch of Knee Walls in my house that I just re did. If you are using fiberglass it needs a air infiltration barrier on the outside. Also usually the plywood subflooring stops just outside the Knee wall. The area below this needs to be plugged so any air leaks from the first floor ceiling below the second floor don't find a path out that opening. I researched this site and found lot's of details on what to do.