antique attic insulation


Old 03-18-01, 07:52 PM
Able Sashweight
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Here's the situation. I'm in the California Central Valley, where winters get to 30 and summers to 100+ . This is an 80 year old 33 x 33 foot SF square brick house. The ceilings are lath and plaster, with all of their original coats of paint, some oil based, and some latex. The mansard style roof means the attic is huge. It is well and passively ventilated. There is no roof insulation. The attic floor insulation is old 3 inch Celotex batts of mineral wool, over about half of the area. Its generally matted, dusty, covered with rodent droppings, and with the occasional rodent nesting burrow. I think I've evicted all of the rats. Some of the batts I've pulled up to expose the know and tube wiring for evaluation. The kraft paper vapor barrier crumbles at touch. The ceiling joists are partly 2 X 3 and partly 2 X 4. In about 5 years, I want to finish out the attic. For now, I want to be temperate at an affordable price.

Here's the questions:
A. I want to shop vaccuum out the dust, dung and debris. Is it worth trying to save the old compressed insulation? (I'm thinking not).
B. Can you suggest an insulation strategy which gives me access to the wiring for gradual updating (pulling load off the old circuits onto new ones), and which lets me reuse insulation when I eventually convert the attic into living space?
C. Does my situation require a vapor barrier, or does the 80 years of paint on the plaster serve well enough? If this isn't adequate, then how can I vapor barrier it, especially since "floor" is the uneven back side of lath and plaster, and since I want to lift this stuff up occasionally for electrical work.
D. Are the kraft paper vaper barriers any more durable these days, or do they all self decay (probably due to the high sulpher/acid content of the paper)? If they decay, does everyone expect to replace this stuff periodically?
E. This Celotex stuff isn't asbestos, is it?

To start the debate, I'm considering furring out the short ceiling joists to the height of the 2 x 4s, laying 3 1/2" Miraflex into those bays, and then crosslaying R25 or some such thickness of Miraflex.

I'm shy about standard fiberglass because I don't like the idea of breathing invisible particles that make my skin itch. When the attic remodel happens, I'm thinking of leaving the 3 1/2 inch layer under the attic floor, and moving the R25 layer to the walls and ceiling.

Sorry this is so lengthy.
Able Sashweight
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Old 03-19-01, 01:19 AM
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Location: Arlington, WA
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Albe, I would remove all of the old Celotex batts, use a shop vac to get the dust, etc. out of the attic, then lay in ENCAPSULATED fiberglass batts. These will greatly reduce the amount of glass particles and "itch" that escape from the batts. The 2X3 and 2X4 joists that are in the house now work fine for ceiling joists, but won't be large enough when you finish off the attic. Ask your bldg. inspector how large of joists you need to install to support the floor of the finished attic, then install them. The size of those joists will determine the "R" value of the insulation you will be installing. Once you get that phase of the project completed, get back to us and we will take you through the next steps.
Old 03-19-01, 07:05 AM
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Think about renting a pnuematic nailer when you sister in the new floor joists. They push the nail in instead of beating the nail in. This will save your plaster ceilings.
Old 03-19-01, 10:29 PM
Able Sashweight
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lefty: we're in sync. thanks.

resqman: thanks for the nailer tip. you probably saved my ceilings.


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