Unconventional attic insulation (XPS)?


I've got sheets of 2.5" XPS (R-15). I'm considering placing a layer on top of the existing blown-in insulation.
Any idea if this is a safe/sensible thing to do? The XPS will be supported by trusses and won't compress the blown-in insulation.
Fire hazard?
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Borrall Wonnell wrote:

Probably that. Plus, it would trap moisture within your current insulation.
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Moisture barriers go down first, if any warm air leaks up into the attic it will condense and mold up the insulation. The foamboard would go down first, then the blown in.
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Borrall Wonnell wrote:

Your blown in may already be compressed. It should be over the trusses at least a foot deep.
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It's not a foot deep, at least not where I measured. Methinks a scouting trip to the attic is in order!
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On Thu, 11 Mar 2010 07:24:13 -0800 (PST), Borrall Wonnell

If mold/mildew is of concern there should be one insulation barrier, and that insulation barrier should be closest to the living quarter planes in the attic space. Your insulation material above the moisture barrier should allow water vapor to pass thorough it.
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Based on advice given here, I've decided to scrap the idea. If I'm going to add more insulation it's got to be blown-in.
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Borrall Wonnell wrote:

Why is that? It is easy to lay batts of fiberglass over blown-in insulation.
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