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Laguinaga 11-28-2013 06:50 AM

Attic insulation in between rafters
Hello everyone.
I live about 25 minutes west of Chicago. I wanted to add insulation to my attic. I bought R-30 unfaced insulation. The idea was to lay this over the existing insulation. When I went to start my project, I noticed that there was hardly any cellulose insulation in between the rafters. In some spots I was able to see drywall. Instead of laying the unfaced insulation on top of the rafters, I had to insulate in between the rafters on top of what was left of the cellulose insulation with the unfaced batts. My whole attic was done this way. The job took me about 5 hours and let me tell you, it was the toughest job I've ever done considering I had to lay down to do most of the job. Did I do this correctly? There is a lot of conversation about barriers and when and where I should use them. I'm hoping that what I have done is ok.
Thanks for reading and for all of the info.

joecaption 11-28-2013 07:18 AM

Did you leave the soffit vents clear?
Did you air seal any places where wiring, plumbing, ceiling fixtures were before insulating?
May have been better to have returned the fiber glass and done blow in instead.
Hind sight is always 20/20.

Laguinaga 11-28-2013 09:23 AM

Soffit vents were left clear. No air sealing was done. The Fiberglas batts were bought a couple of months ago because of a rebate. After getting into the project, blown in would have been the best idea. To late for that now unless I absolutely have to rip out the stuff I just put in. Thanks for anymore input.

Davejss 11-28-2013 10:09 AM

I like to top-off the existing cellulose to the tops of the joists, then run your fiberglass perpendicular to the joists, adding or adjusting your soffit baffles as needed.
If your home has cellulose chances are you may have a poly vapor barrier between your drywall and your joists. If not....well it's too late now.
I'm sure what you did was a hell of a lot better than doing nothing, and I'll bet that your heating bills will prove it.

Laguinaga 11-28-2013 11:15 AM

Thanks for the input. Should I worry about condensation and mold issues?

joecaption 11-28-2013 07:57 PM

No, but by not doing the air sealing you only did 1/2 the job and will not get the full fuel savings.

Gary in WA 11-29-2013 12:06 AM

Joe is spot-on. Air sealing is very important; Start in the basement/crawl- air seal the holes, etc. as that is where the incoming air supplies the attic especially when soffit intakes are minimal. There are also convective loops in your attic, robbing you of R-value, they are able to enter your low-density insulation from the attic side;

I would add a layer of cellulose over the batt as this will crust over for stopping wind-washing of the batt. (Or house wrap like Tyvek, after air sealing; More later on vapor barrier per location....


Gary in WA 11-29-2013 10:09 PM

If your location requires AC during the summer, you don't want/need a poly vapor barrier under the attic insulation to stop moisture there;

You should have a vapor retarder under the cellulose.... if not- a faced (asphalt coated paper) fiberglass batt should be in direct contact with the drywall ceiling;

Keep in mind, without a vapor retarder, any moisture from below (minimal through vapor diffusion, major through holes/gaps around wiring/plumbing chases and overhead fixtures) will move out through the exhaust vents in/near ridge. To save a lot of work; you could paint the ceilings with a low permeability product to act as a vapor retarder in place of the missing one. Box stores even carry various brands.

The attic ventilation baffles stop thermal bridging (read heat loss) where the insulation touches the roof sheathing, keep a ventilation channel clear for positive venting, also direct the air flow past the fibrous (air permeable) insulation. If low clearance at the rafter/ceiling joist area, stack/glue some rigid foam boards there to maintain at least minimum wall insulation (R-20) for your area over the exterior walls;


Laguinaga 12-01-2013 09:34 AM

Thanks for all of the input. I think what I'll do now is add insulation perpendicular to what I already have. Thanks again

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