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Vapor Barrier for blow in fiberglass in an attic.

Jigs-n-fixtures's picture

We currently have an asbestos abatement contractor removing vermiculite from the attics of two 1930s era houses.  Which will leave them without any insulation in the ceilings. 

I plan to go in after they are done and blow in fiberglass.  There was no vapor barrier in the original construction.  The encapsulent the abatement contractor is applying may be impermeable enough to function as a vapor barrier.  I have written the encapsulent manufacturer for thier advice to find out. 

But, assuming the encapsulent isn't a sufficient vapor barrier, does anyone have suggestions on what we could use that isn't going to be too difficult to install in an enclosed attic? 

Bear in mind that if the 1930 (post #206945, reply #1 of 5)

Bear in mind that if the 1930 plaster ceilings are intact and relatively crack-free, and if they have the usual 5 coats of oil paint, that's a pretty darn good vapor barrier.  The areas you need to worry about are the tops of studwalls, around light fixtures, etc.


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No Plaster (post #206945, reply #2 of 5)

The interior on most of my buildings, is a 1-inch thick, fiberous materrial similar to homosote, that had a smooth side on it.  On some it is the only insulation in the walls.  There is no insualtion shown anywhere on the historic plans I have. 

Some of the buildings, those that were normalyy used in the winter, were remodeled/updated in the fifties, by tearing out the interiors, installing fiberglas bats in the walls, silver cloth sheathed wiring (with grounds) and drywall.  They also got white porcelan metal kitchen cabinets, with formica counter tops.   The formica was the "boomerang" pattern in yellow, blue or pink, with aluminum edging.   This is also the time frame when the vermiculite was installed in the attics of many buildings, as it was relatively easy to do with out a major project.   

Where are you located? The (post #206945, reply #3 of 5)

Where are you located?

The problem with adding a vapor barrier at this late date to one area of the house is that you still have vapor migration happening everywhere else.  If all that vapor gets to condensagainst your vapor barrier, you are in for a world of hurt.

Instead of blowing fiberglass, why not use cellulose - it's a little denser and doesn't permit air to pass as easily as fiberglass... plus it will release and pass water vapor instead of condensing it.

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Salmon (post #206945, reply #4 of 5)

I'm in Salmon, Idaho. 

We tried sourcing cellulose, but the one lumberyard in town doesn't carry it, and it is a three or four hours one way to big towns where we might find it. 

Were kind of out in the boonies here.  Building codes enforcement and inspection only started five years back, so there are a lot of iffy things that were done in the past, and a general lack of knowlwdge on how to build right. 

So, right now we have bare attics, and are going to update the wiring. before we install the insulation.  I guess I could take the approack that the buildings lasted fifty years with no vapor barrier and leave it out. 

This might (post #206945, reply #5 of 5)

This might help:

http://www.energystar.gov/index.cfm?c=home_sealing.hm_improvement_insulation_table

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