I did a lot of googling to try and come up with an answer, but I
couldn't find anything addressing my situation.
I have a standard early 1980s suburban house in Texas with a vented
roof. The A/C unit ductwork is in the attic, but only the attic floor
is insulated (blown fiberglass). Obviously, this isn't an efficient
use of the A/C unit since the attic heats up the cool air in the
ductwork before it reaches us. However, we have a very good A/C unit
(home's original owner was an HVAC engineer) with a fully programmable
thermostat and smart home layout (only 2 windows face west), so our
electric bill never gets beyond $250 even in the nastiest summer.
Even so, I'd like to improve the attic temperature so the A/C won't
have to work as hard.
I've researched local insulation companies, and they push the spray on
radiant barrier (cost ~$2500) that's applied to the roof deck. We
can't use the foil radiant barrier because it would block our TV
signal (antenna in attic space) & cell reception (no land line). I
don't mind the price, but anecdotes that I've found range from "didn't
do anything" to "dropped my attic temp 30degrees". The one
insulation installer who came and looked at our house admitted that
radiant barrier wouldn't have a great ROI for us -- it'd probably take
~7-9yrs to fully pay for itself.
However, I've been looking at open cell spray-on foam insulation for
the roof deck -- specifically Sealection 500 -- and every review I've
seen said that it works beautifully. Ideally, it's supposed to be
used with an unvented attic, but I was wondering if it'd buy you
anything in a vented attic. My semi-educated guess is yes, but I'd be
interested in hearing educated opinions.