attic insulation 101

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  #1  
Old 12-14-09, 06:16 PM
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attic insulation 101

I have a 1 1/2 story house, with multiple side attics, and 1 top attic. As for the top attic, the insulation only needs to be on the ceiling of the room below, obviously with the vapor barrier under the insulation. But, what about side attics? Are they insulated the same way? What about the exterior walls of the side attics. Do these side walls that are exterior walls need to be insulated and have a vapor barrier as well? Thanks.
 
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Old 12-15-09, 06:48 AM
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You need to choose between insulating the slope all the way to the eaves, or insulating the slope, kneewall, and floor/ceiling. Both are options, just use only one.

What do you have for venting, ie soffit, and gableor ridge?

Here is a good link related to capes with those darn slopes.

Welcome To Home Energy Magazine Online

Bud
 
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Old 12-15-09, 08:41 PM
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there are a couple of gabel vents, but not sure if they actually are doing what they are supposed to.
As for you options, just to be sure that I am correct, I can insulate the floor/ceiling & the knee wall, or the knee wall & the slope, up to the eaves, correct? Or did i not understand this correctly? Also, what about over insulating? Is this possible?
 
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Old 12-16-09, 07:19 AM
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There are two areas of slope. One is exposed to the side attic, the other is the sloping ceiling for the conditioned room. The options are, the ceiling of the room, down the slope ceiling of the room, down the knee wall, air seal below the knee wall (see link), and then the side attic floor/ceiling from below. No insulation is required in the exterior side walls with this.

OR: the ceiling above, down the slope ceiling of the room, and then continue down the slope ceiling inside the side attic. Yes, all exterior side walls would need insulation here.

Do you have soffit venting?

Bud
 
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Old 12-16-09, 05:43 PM
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From what you are describing, it sounds like I have the first option that you are describing. The only issue is that some of the knee walls in the side attics do not have insulation in them. As for this, is there any way to install a vapor barrier on a finished wall, since the vapor barrier goes on the warm side of the wall? Finally, I do not believe that I have soffit vents. I have looked several times, and only found 2 gable vents, and no soffit vents. So I also think that some attic vents maybe needed as well.
 
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Old 12-16-09, 06:18 PM
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If you have an overhanging eave with solid soffits, then vents can be added. If your home style has no overhang, then other options are required.

Do your side attics have a floor above the joists forming the ceiling below, or are they open beams with insulation (maybe) in between them. The air block directly below the kneewall is very important to prevent cold air from circulating in the cavity between the floor and the ceiling below, across the entire room.

To add insulation to those kneewalls, seal where the wall rests on the floor and around any electrical outlets/switches. Also seal all holes where wires or plumbing pass through. Then fit kraft insulation between each stud with the kraft towards the warm side. Don't fold the staple ears out, just rely on a tight fit. You can cover the exposed insulation with tyvek, but not plastic. Anything that has a high permeability can be used.
Article on vapor barriers and vapor diffusion retarders: Energy Savers: Vapor Barriers or Vapor Diffusion Retarders
I'm not concerned about the kraft not being a continous barrier as the sheetrock is an air barrier and the paint provides the vapor resistance.

Make sure your access door to these side attice is well air sealed and insulated.

Bud
 
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Old 12-17-09, 05:01 PM
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some areas of the roof I believe have an overhang, where soffit vents could be added. What about the areas that do not have soffits? would regular roof vents work? Secondly, the attics in which I have looked in, (I have 3 total) have a floor, and the areas in which I can see through the cracks, I can see insulation in there. As for the access doors, I do know that these need some serious improvement, I just need some type of reference to look at for this. One door, i think is a board, with a box attached to it, the box faces the attic side. I am willing to guess that the "box" is full of insulation. As for the other access doors, they are just a piece of wood. I am thinking of adding weather strip to these as well as stapling insulation to these as well. Any thoughts?
 
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Old 12-17-09, 05:18 PM
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Roof vents will work. There are edge vents that go where the drip edge is, never used them but may require some shingle work. (warmer weather). Attic doors all seem to be different, so most have to be built to fit. Air seal is #1 and insulate. They need as much insulation as possible.

Of key importance is the air block that will keep cold air from circulating under the kneewall, in the joist cavity where it will cool off the ceiling of the room below. If you have boards, you may need to remove a section to get something into that space to block it.

Bud
 
  #9  
Old 12-20-09, 08:13 PM
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how far down in the knee wall do I need to go to seal the point of concern? Do I need to go down to where the knee wall meets the joists for the room below? As for venting, do you know of any diagrams available? Do I simply need roof vents, or would a combination of soffit and roof vents work better to give the attic areas a "flow through effect"?
 
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Old 12-20-09, 09:09 PM
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The space I am referring to below the kneewall, is below the wall, in the joist cavity. Their pictures aren't perfect in the link above, but what they are trying to illustrate is open joist cavity from the ceiling below, as it passes under the kneewall, it can circulate warm air out into the cold area below the side attic and return cold air into the space above the ceiling below. Any fiberglass insulation in the floor below the side attic will not block air flow, so a solid block needs to be placed directly below the bottom of the kw to divide the cold joist cavity from the warm.

A combination of roof and soffit vents would be a must to function in a cape with side attics/slope/upper attic. Here is another link:
http://www.crrel.usace.army.mil/libr.../MP02-5778.pdf

Bud
 
  #11  
Old 12-22-09, 07:17 PM
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what type of solid block needs to be placed below kw? Are we talking a vapor barrier, framing, etc? Secondly, as for the attic venting, I see how the proper venting will isolate the attic air from the conditioned room air. Would proper venting make a substantial difference in the house temp during the summer months as well? Currently, during the summer months, my second floor is EXTREMELY HOT!!! Thanks for the advice
 
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