Insulating Knee Walls in Michigan Bungalow


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Old 12-24-13, 07:54 PM
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Insulating Knee Walls in Michigan Bungalow

I'm purchasing a home in michigan and I want to make sure the attic spaces and knee walls are insulated well. It has roof cap vents only, no ridge vent no soffit vents, and no gable vents. The insulation is currently in the rafters and on the floor but not on the inside knee walls.

I've read a couple things showing that you can have either a) conditioned space with soffit vents and a track up each rafter to a ridge vent or b) insulate the knee walls and the floor and seal below the knee walls essetially turning the attic space into a very cold winter space or a very hot summer space.

Can plan A be done without soffit and ridge vents. That is somehow create a "conditioned" attic space with just the cap vents?
 
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Old 12-25-13, 06:40 AM
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Not awake yet, but you say the rafters are already insulated. If fiberglass or any permeable form of insulation, it can't be sealed and needs venting top and bottom. Because the shingles are water proof, no drying through them. Thus you end up with a VB on one side (top and wrong side) and either a second VB (bad) on the inside or no VB on the inside which allows moisture to migrate through and accumulate. For a sealed rafter configuration there needs to be a low permeable insulation, like spray foam or very well detailed rigid foam (called cut and cobble) installed to a thickness that will insure the inside surface remains above the dew point.

That last part comes into play when you consider insulating the knee wall after the rafters are already insulated. Those side attics will get very cold even with the rafter insulation, thus surfaces may drop to below the dew point. IMO, with a knee wall, cover the back with an air barrier, insulate it well above code, remove the rafter insulation and vent soffit to ridge. How that fits what you have is to be determined. Later I can pull up some links to help you decide. Xmas to attend to. We just got our power back so I need to find out where we will be celebrating. Three families have been enjoying themselves in a hotel, while I kept the generator filled. They owe me.

Happy holidays
Bud
 
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Old 12-26-13, 10:44 AM
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I've attached a picture to show the attic.
That is R-13 fiberglass batts shown in the rafters and side walls.
Also attached is a shot of the louvre vent in the front of the house as well as a gable vent.

Should I just take the fiberglass batts off the rafters and put them on the knee walls?

Also I do not really want to mess with the ventilation too much, this is a 1940s house that I assume has been vented the same way for 60+ years, is it adequate?
 
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Old 12-26-13, 01:26 PM
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Ouch, one way or another you have a project in front of you.
That one roof vent looks like it is venting a side attic. If so it is helping to keep the roof cold, but any insulation in those rafters would not be keeping the house warm. Note the snow over that area.

Some tough issues here. You do not have sufficient venting to comply with a vented solution and the insulation in place cannot be used as part of an unvented approach. My guess is that the question you are asking is how to make some improvement without taking on a major project. We see that approach often, both at home and on the forum.

Of the two major approaches, no venting (called a hot roof) and vented (called a cold roof) you can probably rule out the hot roof. The trick to "no venting" is a perfect air seal and lots of r-value. You must prevent inside air from reaching any cold surface and the r-value must be high enough to keep the first cold surface above the dew point. In your climate that would be about 3" to 4" of spray in foam plus 6" of high density batt insulation. I like Roxul. But that would be the entire length of the rafter from soffit to ridge, major, major.

That takes you back to kneewall or rafter, but does not address the slopes or attic above. but does require some venting.

Let's wait for some of the pros with lots of experience to see what they can suggest.

Bud
 
 

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