On Nov 1, 4:23 pm, wrote:
I want to upgrade my attic insulation. I have 2x6 beams and old
unfaced R13-R19 fiberglass batts up there. I want to add R38 on top of
the existing insulation. I am in San Jose, CA.

I can do cellulose, which will give me uniform coverage and is the
least expensive option. But I've heard it's very dusty (even after
it's done, my furnace hot air ducts runs in the attic), not easy to
deal with if I need to go up the attic and do something, and boric
acid/ink may give off bad VOC.

I can do blown-in fiberglass, but how do I ensure the contractor won't
fluff the insulation? I am also not fond of the idea of lose
fiberglass floating around in the attic. They may get sucked into the
furnace duct and gets into the house.

I can do fiberglass rolls. Less chance of lose fiber floating around,
and R38 is R38. But it may not insulate as well as blown-in since it's
layed on top of my existing insulation and the coverage won't be as
uniform as blown-in. But advantage is I can move it out if I need to
go up and do something.

I am leaning toward the 3rd option. Assume the contractor does a
decent job, will it provide adequate insulation? Between a reasonably
installed (ie, average, not perfect) batt vs blown-in cellulose, how
does the fiberglass batt compare? If it's 80% as good, then I think I
am fine with it...

Thanks!

Raymond

Ray-

fiberglass rolls at 90 deg to current rolls...keep clear of roof
underside & allow for eave to ridge venting
Any gaps between the layersis just more dead air space...free
insulation.

btw are you adding R-19 to get up to R-38 total or adding R-38?

San Jose is a pretty mild climate so R-38 total should be plenty.

I'm in Orange County & I put R-30 in 1980; fiberglass rolls that I
just rolled back to do some attic work

The R-30 works pretty good for me but the old house is not as tight as
it could be due to other issues.

IMO blow-in cellulose is good stuff, it works but its a mess if you
ever need to revisit the attic. I hate it!

My parent's house has blow-in cellulose & it's been keeping the place
warm for ~30 years.

cheers
Bob