Upside down attic insulation

bfg9kSeptember 7, 2010

Our 1500 sq ft ranch's attic is very under-insulated. During last summer's moving-in renovations all of the 55 year old windows were replaced, all cracks caulked, etc., making it pretty free of drafts. However the heating bills were still $400/month with the thermostat at 66F (oil heat - 30 year old furnace). The attic has a double layer of 4" fiberglass batts in place. The bottom batt is kraft-paper down, then the top batt is kraft-paper up. There's no vapor barrier, but during the renovations we used copious quantities of BIN shellac primer on the ceilings (to seal in cigarette smoke residue, ick) and I understand that makes a fairly decent moisture barrier.

If I were to go and add a whole bunch of blown in cellulose insulation to bring the R value up to around 40, should I either remove the top layer of batts, flip them over, or leave them alone?

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How is the attic ventilated, what is the attic used for, are there any HVAC ducts in the attic, what is the slope of the roof and how high is the ridge above the attic floor?

The purpose of kraft paper facing is to form a vapor retarder if it is stapled to framing at its edges. the purpose of attic ventilation is to allow moisture to escape from the attic space.

    Bookmark   September 7, 2010 at 12:06PM
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The attic has a full ridge vent and gable end vents,the, don't know offhand. Let me guess - 14 degrees with a 5' high center and 40 foot width house. There are no HVAC vents anywhere in the attic (or the rest of the house). The batts are not stapled to anything, as I found when I installed a whole house fan earlier this year.

    Bookmark   September 7, 2010 at 12:14PM
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A rodge vent needs soffit vents to work properly. Gable end vents will only allow half of each end of the attic to vent.

Adding/clearing passages for soffit vents will increase the attic air flow and heat transfer tremendously.

    Bookmark   September 7, 2010 at 12:23PM
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can't have two vapor barriers within a bldg assembly.
condensation forms between the two vb's when attic dewpoint is reached.
remove paper backing off top batt and install blown
might be easier just to remove top batt and blow insulation

best of luck

    Bookmark   September 7, 2010 at 3:12PM
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Go up there with a utility knife and slit the upper most paper or take it off, what ever is easier.

    Bookmark   September 7, 2010 at 11:16PM
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You do not need any implement to remove the kraft paper, simply peel it off.

    Bookmark   September 8, 2010 at 9:12AM
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Before you add any more insulation I would be meticulous and go through and seal any penetrations in the ceilings, every wire hole, plumbing chase, electrical box, etc. Make sure the access door has insulation/sealing equal to the ceilings. The R-value assumes no air movement between the areas. Insulation is all about the details. If you miss 1% of the area, you lose alot more than 1% of the insulating value. Its like having a 1% hole in your bucket, you lose more than 1% of the water.

    Bookmark   September 8, 2010 at 11:05AM
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