Here is a more detailed scenario for retrofitting a house with insulation.
It's a 2000 sq ft slab on grade in texas, 8' ceilings, 5' attic at peaks,
currently has 4" of fiberglass betwwen the ceiling rafters in the attic.
Was going to add cellulose for benefits: better r value than fiberglass; 30
to 40% radiant barrier; "seal" of attic (which fiberglass cannot do).
Now it looks like cellulose has these problems: invites mold; decomposes
over 20 years; loses its inflamability over 20 years; makes a constant layer
of dust in the house.
So back to the original situation, wanting to increase insulation
significantly, can this be done by fiberglass and how many layers can be
added in an attic? Also there is no radiant barrier, should one be added?
What is rock wool and would it be better than fiberglass?
Also needing to insulate a 4" airspace with 2" of insulation but cannot find
anything to do it with at retail outlets, except maybe use an electric
carving knife to split some 4" thick insulation but then the r value is
minimal...the insulation manufacturers make a fiberglass board insulation
with aluminum facing, but it cannot be purchased by the general public, only
licensed contractors can buy it supposedly.