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Old 12-18-2011, 03:22 PM   #1
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Reusing Deteriorated Insulation

First I want to thank all of the folks who help make this a wonderful site. I recently purchased my first house, and sites like this have been helping me tackle a bunch of improvements.

Since winter has rolled around, I've been crawling around the attic improving my insulation. I'm pretty sure that whoever insulated the attic previously did a con job. I've found that the attic has either badly deteriorated fiberglass or blown in insulation around the center third of the house, of course without a vapor barrier. Outside of that, nothing. If you just poke your head up into the attic, everything probably looked great when first installed.

To fix this, I've been laying down R-13 paper backed fiberglass rolls in areas that don't have insulation. Where there is insulation, I had the bright idea to put down a vapor barrier and pile up the old insulation as if it were blown in. After I get all this done, I plan to add a second R-30 layer over everything that I can reach.

So my question, is it worth it to reuse the old insulation as if it's blown in? I figure that by piling it up I should be able to get the final areas back up to a reasonable R value. However, I haven't been able to find any information/opinions one way or the other.

A second question popped into my mind as I typed this. I have a very low slopped roof. Additionally, the builder put 1x6 or 1x8 boards (I haven't take the time to measure) running perpendicular to the rafters 6 - 8 feet from the edges. I'm assuming as running boards for electric. As a result, I don't really have access out to the edges of the house on those two sides. Are there any tricks for getting insulation out to the edge of the roof? Right now I've been using a piece of EMT to push/pull the insulation out. But it sometimes rips up a bit of the fiberglass.

Thanks in advance.


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Old 12-18-2011, 03:50 PM   #2
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Where is the home?

You may not need a vapor barrier and mixing layers (i.e two vapor barriers) is a recipe for disaster.

Best thing to so is to seal up that exterior top plate.

What is the ventilation like?


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Old 12-18-2011, 04:27 PM   #3
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The home is in Livermore, California. Temps tend to range from 30-105 (110 - 120 on a bad year). Day/night temperature swings tend to stay around 30-40 degrees. We don't get much precipitation (15" a year), but morning fog/cloud cover from San Francisco bay isn't uncommon.

I don't think there is a pre-existing vapor barrier. If there was one, it has deteriorated along with the insulation. Also, given that the chunks of insulation are normally golf ball size or smaller, with the occasional fist sized piece. I was figuring that if small pieces of an old vapor barrier were mixed in, there would be enough openings in the reused pieces that they wouldn't trap moisture. But again, this is one of the reasons I wanted to ask about reusing the old insulation.

As for the need of a vapor barrier, I've noticed two interesting things. In some places, it appears that the insulation has bonded to the top paper of the ceiling sheet rock. Scraping with a plastic dust pan can sometimes break it free. If I'm not careful, bits of the paper come with it. I'm assuming that this sticking/bonding, is due to moisture getting into the insulation. Likewise, I consolidated insulation from two bays last weekend, but didn't have plastic for a vapor barrier on hand at the time. When I went back to add the barrier this weekend, the insulation felt like it had started to stick together. It was possible for me to pull up a bay wide section that was 2-3 inches long. However, the slightest jolt would cause it to break down again into small pieces. Again I'm assuming this is moisture getting up into the attic. I haven't seen signs of recent moisture, so I'm also assuming that any moisture is coming from the conditioned parts of the house. Unfortunately, the previous owners waited until the roof was leaking live a sieve before reroofing. So finding evidence of moisture build up is hampered by large areas where moisture got in but didn't damage the roof boards enough to warrant board replacement.

Ventilation wise, I have ~176 round soffit vents, which I believe give me ~132 square inches of venting. Additionally, I have 7x 80 sq. in vents near the top of the hip roof (2x2x2x1 configuration with 1 north facing). I know the soffit vents need to be enlarged to match the top vents. The whole house fan I have calls for 8 sq feet of total vent area if I remember correctly.
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