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Sasmus2927

06:17AM | 10/07/01
Member Since: 10/06/01
1 lifetime posts
Bvhvac
I have an attic area similar to the second picture at http://doityourself.com/attic/insatticrafters.htm - the gabled wall attic.

Currently there is only insulation in one of the flat parts on the side of the house. The other flat and the cathedral portions are not insulated.

Essentially I figure on the flat parts of the roof I need to install about 4 soffit vents per side - or a soffit plug for each section between rafters and then put a baffle in each section to create adequate air flow, cut ventilation holes in the middle "knee wall??" to keep the air flowing and then put baffles all the way up the cathedral ceiling portion to the ridge vent at the top.

Now comes the insulation, I live in the north suburbs of Chicago and from what I can tell the recommendation for attics is about R-49. In the flat part I think all I need to do is staple the insulation in-between the rafters. When it comes to the cathedral part is when I really run into trouble. The "rafter joists??" - the wood connected to the actual roof is only 3 1/2" wide. When I went to look at insulation, R-30 is already 10" thick and I still need to add another R-19. When I looked at what would fit on the 3 1/2" "joists" I would only get R-13 and that is without baffles.

Additionally 1/3 to 1/2 of the attic is finished but there is the 3 1/2" gap between the drywall portion of the room and the "roof" - I'm planning on blowing some insulation in but I will only get an R-13 rating.

The insulation I was looking at is paper-backed/faced - planning on using that as the vapor barrier (facing down).

Questions:

How do I insulate the cathedral part correctly to achieve the best insulation?

In insulating the flat part do I need to lay down something to hold the insulation up so I does not actually rest on the ceiling?

Would the paper-backed insulation create a sufficient vapor barrier or do I need something additional - or should I just use something different and go with the non-paper backed insulation?

When I blow insulation into the 3 ½” gap do I need to put a vapor barrier on the down side – if so how would you recommend getting it in the gap so it does not rest on the dry wall or does it matter?

How big of a difference does an R-49 to R-30 to R-13 make?

In this case would anything really be better than nothing?

Thanks!!!



DH

08:31PM | 10/08/01
Member Since: 09/23/01
242 lifetime posts
Wow, lotta stuff to cover, to start the highet the R value the more insulating value. So R-30 is over twice the value of R-13(typical 2x4 wall). Soffit vents and RIDGE vents are very important, and you should have at least 4sq in of free air per bay, with a 1" air space between roof sheathing and insulation. For the cathedral portion I would suggest ridged foam board, 3" thick is R-25. On the flat portion just roll out unfaced bats, you do not need any support other than the drywall. I wouldnt worry about a vapor barrier in the ceiling, only the walls. Hope this helps.

Jay J

09:02AM | 10/09/01
Member Since: 10/26/00
782 lifetime posts
Absolutely! Make sure the ceiling is vented!

Otherwise, later on, you'll be writing to us wondering why your cathedral is showing signs of mold/mildew.

Consider a skylight too, one that can be opened and closed via a motor. (Velux, for one, makes them ...)

My best to ya and hope this helps.

Jay J -Moderator

PS: God Bless America!

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