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Redoing insulation in attic: Do I need vapor barrier?

Redoing insulation in attic: Do I need vapor barrier?


Old 09-21-01, 09:50 AM
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We have a 2-story home build in 1922. The attic is unfinished and we had problems with ice dams last year (1st year living in the home). Currently there is very old rock wool insulation in place -- only about 3 inches thick, with no vapor barrier underneath. The insulation is in bad shape - shreaded and very dirty, so I was thinking of tearing it all out, then completely redoing the attic with new insulation. My question is -- should I put in a vapor barrier before I blow in new insulation (prob. cellulose)? I'd assumed that was the correct thing to do, but the house has done well with no vapor barrier in place. Could adding one cause potential problems in the future?

- John
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Old 09-24-01, 05:59 AM
Join Date: Jul 2001
Location: Indiana (formerly Massachusetts)
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Why wouldn't you just go over the existing rockwool with unfaced fiberglass batts or blow in new cellulose insulation. As long as the insulation is not wet, it is serving a function and it would be messy and a pain to take out all the old rockwool when you can just go over it.

Good luck!
Old 09-24-01, 06:22 AM
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The existing rock wool is in very bad shape -- dirty, shredded, and it was installed so that a paper backing is face up (facing up towards the undeated attic). I worry that if I add more insulation on top of the old rock wool it could cause a problem due to that paper layer (not sure if it was meant as a vapor barrier or not). So I've decided just to get rid of the old stuff and do it 'right' from scratch. But I'm worried about what is the 'right' way to do it. I talked to others who redid insulation in their old houses and they all put down a vapor barrier with no problems, so unless I hear a good reason NOT to do so, that's the route I'm planning to go for now.

- John
Old 09-25-01, 01:27 PM
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Putting a vapor barrier in the ceiling with fiberglass could create severe condesation problems. If you've ever see new homes under construction you'll never see it. The main reason for putting it on walls is to keep the condensation in the insulation for discoloring the wall board.

You can take the rock wool out, it's useless but you will have to wear a mask that is rated for carcenogenic fibers. They usually sell for abot $33.00. Put the material in plastic bags and tie tightly to prevent contamination of the rest of the house. Wear long sleeve shirts and plastic gloves. Plan on throwing the clothes away as it is almost impossible to de-contaminate them.

I removed the rock wool from my mom's house 30 yeaars ago and replaced it with a 3 layer radiant barrier. It is far superior to any fiber glass you could put up there. It is clean handling, no fibers or chemicals to cause cancer or asthma. Fiber glass is about 10% efficient against heat energy, radiant barriers about 97%. It will really cut your A/C requirements.

I recently reinsulated a church that had your problen. In this case I made a tamper and tamped lightly the rock wool down and installed a radiant barrier above it. The radiant barrier also acts as a vapor barrier but does not cause condensation.

If you do this, I would also recommend that you see your Sherwin Wns paint dealed about "Radiance" paint. If you like pastel colors such as bone, white, etc., you can paint the inside of your exterior walls. This paint is 40% effective, so, you can insulate your walls with is paint. You can get standard paint, tinted to match for the interior walls.

If you have any questions about method or material source, let me know.

Enter into your search engine; "radiant barriers" or "reflective insulation".

Thank you for considering my opinion.
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