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Old 09-29-08, 12:16 PM   #1
Daox
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Default Attic ventilation and insulation

One of my projects that I am really wanting to get done before it gets too cold to work outside is adding additional insulation to the attic. It currently has about 1.5" of rockwool insulation and 4" of fiberglass over it. This gives me roughly an R-17 value for attic insulation. This is fairly low compared to the recommended R-50 rating it is suggested to have! So, I have spent the past few weekends and extra minutes here and there cleaning up the mess that the roofers made while replacing the roof this year.

Now I'm getting to the point at which I need to start doing something about the ventilation. The roof currently has a ridgeline vent put on, but nothing else. So, I was going to replace the current soffit with soffit with vents in it.

However, this now brings about another problem. My roof is a bit odd. It sits lower than a normal roof and creates a chamfered angle in each of the rooms similar to a 1.5 story, but no nearly to that effect. The chamfer is about 1.5 ft down from the top of the ceiling. See the picture below for a wall section view. My problem is that I need to insulate that small area the best I can. I'd really like to use some rigid foam in there to get higher R-values, but I have to leave room for venting. Ideas?





I also have another idea/problem. I'm planning on blowing cellulose over the fiberglass. This is going to pack the fiberglass down to some degree and decrease its insulating value. I'd like to avoid wasting what I have and preserve this insulation. I was thinking of laying down some plastic over it and stapling it down, or cardboard or something to prevent the cellulose from derating the fiberglass. Got any ideas for me?

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Last edited by Daox; 09-29-08 at 12:18 PM..
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Old 09-29-08, 02:50 PM   #2
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Do you have any soffit vents at all? I had some and then added probably 50% more but our roof construction was a bit more typical. Adding the air channels was the hardest part. I used a sawzall to remove the existing boards and then added vents. I made the channels out of radiant barrior OSB cut to fit. They do make foam channels that you may be able to use. You then might be able to fill underneath with spray foam. You may also be able to build your own channels using 1 or 2 inch rigid foam. Are your rafters 2x4 or 2x6 construction?

As far as covering the insulation in the attic, you may not want an impermeable surface since you want moisture to be able to escape. At least that is how insulation is set up here. If that is true for you, you could probably try window screen. It comes in rolls and would be pretty easy to install.
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Old 09-29-08, 03:09 PM   #3
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Nope, no soffit vents at all. I'm sure some air leaks in from around the trim, but no actual vents.

I was planning on using those foam or plastic chanels if need be. I might have to put two together to extend up far enough, but we'll have to see.

The roof is 2x6 construction, so I at least have a few inches to play with for insulation.

I like the screen idea. I will have to see how that compares to the plastic. I had thought about it being a vapor barrier. I just forgot to mention in my post that I would just poke a bunch of holes in it so it can breath.
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Old 09-30-08, 04:04 AM   #4
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Quote:
Originally Posted by Daox View Post
I would just poke a bunch of holes in it so it can breath.
How large of an area are you talking about?
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Old 09-30-08, 06:07 AM   #5
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The attic is right around 700 sq. ft.
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Old 10-08-08, 10:44 AM   #6
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Well, this is the week and weekend I'll start doing the work. The first concern is getting the soffit ripped out. There is aluminum soffit material on it currently with wood above it. So, it all needs to come out so I can get access to the highlighted roof area from the picture above. With that all ripped out, I'm planning on cutting up some foam board insulation to shove up there and lay on top of the ~1" of rockwool that is currently in there. This is about as good as well insulated as I think I can get it.
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Old 10-08-08, 12:00 PM   #7
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Daox- I found this product last week. Products :: Wraptor Plus :: Insulation Solutions
It claims to be used as a house wrpa but I don't see why you couldn't use it for what you're wanting to accomplish. It says it's breathable. Just thought I'd share.
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Old 10-08-08, 12:35 PM   #8
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How would you suggest using that for my application?


Edit: Ooooh, you mean for putting over the fiberglass, right?
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Last edited by Daox; 10-08-08 at 12:41 PM..
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Old 10-08-08, 01:01 PM   #9
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that's what I was thinking.
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Old 10-10-08, 06:51 PM   #10
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There is a difference between vapor barrier and house wrap. House wrap like Travek isn't a moisture barrier. It's designed to keep air out, but not moisture. And in an attic you want a vapor barrier and punching holes in a true vapor barrier isn't a very good idea. You have to remember that wet not only occurs from condensation, but a greater potential for water problems in an attic is from a leaking roof.

Think of it like this house wrap is a wind breaker- it'll keep you warmer by reducing your resistance to the wind, but once it starts raining you're going to want to wear a rain jacket...cause you're gunna get soaked when wearing a wind breaker in the rain.

Properly installed insulation with a vapor barrier will keep moisture from building up in the insulation. There is no need to punch holes, in fact it'd be detrimental to the entire project.

The idea of insulation is to trap air not to release it. Don't worry too much about letting your house breath, it will and it's better that it does through the walls than through the roof, because at least if it's in your living space you're more likely to spot any problems before they get out hand, where as left in the attic you could have problems and it'd be years or major damage when you notice it.

Just because you're trying to save money as a DIY'r don't cheat yourself by doing things cheap and half-assed. It can and will bite you in the end, believe me I know.

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