On Apr 1, 7:31*am, wrote:
I sat through a free dinner (chicken or shrimp) and heard a guy try to
sell me roll-out multi-layer aluminum foil insulation (apparently with
mylar in the sandwich). *It is perforated so as to allow moisture
through, and installed over top of the fiberglass/cellulose/whatever
in the attic. *It is claimed to reduce heat gain in the summer and
heat loss in the winter.

I don't doubt that it would be effective to some degree, but I gather
that the optimal placement for heat-gain reflective insulation *is on
the underside of roof rafters, and I think that the optimal placement
for heat loss would be on the warm side of the house in the winter,
i.e. just behind the drywall, with an air gap. *Laying the stuff over
12 inches of fiberglass is optimal for neither situation, but it still
might be ok.

Does anybody know what increase in effective r-value you might get
this way? *I live in the north and don't use AC, so *reducing heat
loss is generally more important a consideration. *I searched for a
while with google but didn't find anything very relevant.

I have truss rafters, incidentally, and installing this would be a
total pain in the ass.

You dont know if you ate chicken or shrimp!