My version of the attic insulation question...

[Anonymous]

Hi -- my variation on the popular question about attic insulation...I've read so many things about this, but just feel like I can't get the full answer to what I'm asking...

I have a small home (near Chicago, IL) with a pretty bad ice daming problem, and a poor storage problem. I want to put a floor in my attic for storage, but also want to improve the insulation situation. So here's my story:

My attic has blown insulation, probably 12" (8" joists). There is no ridge vent, no soffit vents, and no eaves on our house -- the gutters attach to the outer wall, shingles go right to the gutters. The attic has a single motorized exhaust fan at the top middle of the roof (gable roof) and vents on the exterior walls at both ends.

So, I want to alleviate the ice dams, and put a floor in the attic. But based on what I've read, if I put a floor in the attic and compress the insulation there (to the height of the joists, or 8") I'll be making the insulation situation worse, not better. So I thought to insulate between the roof joists too. But then I've been told that won't help -- which confuses me: why isn't that added protection against heat escaping to the roof?

So I'm puzzled about what to do next. When I get my roof redone, should I have the roof radically altered to give me eaves with soffit vents, and a ridge vent? I shudder to think about that that would cost. If I insulate between the roof rafters, would that HARM anything, or would it just be a less effective option; or, given that I don't have any soffit-to-ridge circulation anyway, would it have some benefit? Should I put a layer of that rigid foam insulation down before a floor material? Or do I just give up on an attic floor and double overlay the blown insulation with rolls of batting?

For fun (yours, not really mine :-) ) here's a shot of my ice dams:
http://harrisonfamily.org/images/albums/house200402/pages/
P1010024.html

ANY suggestions, two cents, ideas, or recommended readings would be appreciated greatly!!

Thanks all!

Jeff

[Rich]

If you put in a floor and compress the insulation - it's not a problem. It's not a problem there because it's essentially the same thing that happens between the first floor and the basement of your house. Where you will have problems is outside of the framed room you put in the attic. You can insulate the sidewalls and outside the room in the ceiling (like you have now).
Your best bet is to put eave vents in and a ridge vent. This isn't that big of a deal if you are having your roof re-done. You'll just need to check that there is positive airflow out of the eaves into the attic space. Where the new framing is at (or the ceiling of the new room) you will need insulation in the ceiling joists / roof rafters. If ceiling is vaulted you will need baffles in addition to the insulation to allow the air to flow from eave to ridge vent.
Hopefully that all makes sense.

[grumpydasmurf]

What I would do is put down a floor compacting or removing the insulation on the floor as necessary. I would fasten 2" x 2" to the bottom of your rafters. I would then insulate yourr afters making sure the insulation doesnt go all the way to the bottom of the roof deck. Fasten rafter baffles before insulating if the budget allows.

After this is done, you may want to cover the walls with some kind of panelling or board, and build a ceiling just under your gable vents. You may have to crouch a little bit but by doing this you will effectively insulate the attic AND allow for proper ventilation.

Now if you are re-doing your roof, like Rish said, I would do everything I said but close up your gable vents and fan. Then do what rich said and install a ridge vent. Since you have no overhang, installing eave vents will be tricky but not impossible. There are plenty of fascia venting items on the market.

Also if you are replacing the roof, and since your in the Chicago area you will want to install ice and water shield. If you'd like to further discuss your roofing and ventilation options feel free to contact me. I am in the Chicago area too, and as luck would have it I am a roofer.

[Anonymous]

Thanks, both of you, for the feedback! It's helping me understand the impact of all the different variables! Can I ask for a little more detail

...Where you will have problems is outside of the framed room you put in the attic. You can insulate the sidewalls and outside the room in the ceiling (like you have now).

I got a little confused here. Let's say I put the floor in my attic, removing some of the blown insulation and compressing the rest down (I was planning on putting 2x2s on top of the joists because I have a lot of conduits up there, so there'll be about 10" of insulation under the plywood once the floor is in). Then I put rolls of fiberglass between the roof studs. Do you think that would help keep heat from escaping to the roof, and thus help alleviate my ice dams, or do you think it would have little benefit?

Based on what you've said, in all likelihood I'm going to try to get a proper ventilation arrangement in place when I get the roof redone...I'm just hoping to put that project off until I can tuck some money aside for it...

Thanks again guys!!

Jeff

[Rich]

In the floor of your new attic room - you shouldn't have too much worry about the heat transfer to the air space. Right above the floor is where it becomes a problem and along the adjacent walls. In essence, anything that shares a common surface with the "cold" side - which are walls and ceiling of the new attic space. Where you share the floor with the ceiling below is not much concern.

[grumpydasmurf]

Dont put the insulation in direct contact with the underside of your roof deck. That's asking for problems no matter what. You MUST have a space for air flow.

[Rich]

Yep.. as both grumpy and I suggested - baffles need to be installed especially if your ceiling joist is the same as your rafter.. umm.. essentially if it's vaulted.