Attic conversion knee walls
nc116
| Posted in General Questions on
I have a 24′ x 35′ attic that has roof going all the way to floor but with steep pitch. I have t&g ply for the floors, but I am wondering about futureproofing. I will have approximately 4′ knee walls making about 3′ of floor space between soffits and knee wall. Should ply go all the way to the soffit? Or can I leave some insulation exposed for easier underfloor wiring? What’s the best practice here?
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Replies
This article should answer all of your questions: https://www.greenbuildingadvisor.com/article/insulating-behind-kneewalls
If the attic conversion is still in the planning stage consider not doing it for a few reasons.
1 Making the room in the current first floor for a code legal stair is no small feat. Generally, to make it fit the rise of each step is made taller than code allows and the width of each step is shorter than allowed. So, the stair is a trip hazard.
2 Since you are reading this web site energy efficiency must be important to you. Retrofitted half story building like you have preposed tend to be the leakiest building style and very inefficient.
3 The sloped part of the ceiling is almost always so shallow that fitting in code min insulation is the only time I see value in spray foam insulation.
4 How many square feet of this space will have 7 feet of head room after you subtract the stair case? Less than 400 is my guess.
5 If you are lucky, you have a window in each gable wall but they are very unlikely to be large enough to count an egress window so the space can’t legally be used as bedroom.
This article may interest you.
https://www.greenbuildingadvisor.com/article/insulating-a-cape-cod-house
Walta
I tried to ask with more detail a few days ago but noone replied.
This space already has a door to it from the second floor so staircase is not an issue.
Pitch is very steep. Over 500sqft of 7' space.
Rafters are 2x10 but will convert to unvented and use closed cell. Easy to achieve r49 that way.
Collar tiers are 8' long and are at 8' from joists. Windows should be adequate.
Malcolm responded to your other post.
I hate half story building but if you must have one, I say you need the other two things I hate because they all go together so nicely.
Spray foam the roof sheeting from the peak to the soffit and have a conditioned attic.