older attic insulation - overlay or replace


Old 11-08-02, 12:51 PM
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older attic insulation - overlay or replace

I have a 40 yr old ranch house, with attic fiberglass insulation - that seems abit sacked out. Its probably 2.5-4 inches deep in a 6 inch deep rafter.

The house has a whole house fan, so its dusty in the attic.

Should I upgrade the insulation by laying unfaced insulation over the existing stuff (including the wires & wire junction boxes).
Or should I just pull it out (where possible) and slide some new, extra thick insulation in.

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Old 11-09-02, 06:23 AM
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Laying insulation over the existing insulation is fine as long as it is unfaced and the existing insulation is not wet.
Old 11-11-02, 06:20 PM
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I would recommend that you install a 2 layer radiant barrier(RB) over the top of the existion. You have enough space between the top of joist and FG that it will easily go in.

The RB is abot 95% efficient and the FG about 10%. The FG is not that great for A/C anyway.

You might also want to checkout RB paint to greatly increase the insulation value of the walls. These two products combined could save you up to 40% or more.

Enter; radiant barriers or reflective insulation.
For the paint go to Koolcoat.com

Thank you for considering my opinion.
Old 11-12-02, 06:39 AM
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Lightbulb foil bubble wrap around the A/C ducts in attic.

Thanks for the recommendations and suggestions.
I will check out the RB idea.
The attic is complicated because it also has the air conditioner, and air conditioning ducts in it.
I'm thinking I will defintely wrap the a/c ducts with the foil bubble wrap.
The attic heat defintely overwhelms our a/c system whens its 97+ outside.
Old 11-16-02, 06:47 AM
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I thank you for your response.

You could install a two layer, perforated RB in the rafters and the gable ends. The efficiency will drop a bit but you would get 100% coverage. Try a 4 MIL rb at about$0.20 SF/500SF rolls for the ducts. If you can't get these locally I can supply you with them.

If you want a sample let me know. You might find that you can install in the 2x6 joists when you see the material.

Thank you for considering my opinion.
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