Do you have access to the roof? Have you thought about growing grass?

weedmeister, thanks for the suggestion - it's not a truly flat roof in that there's a crawl space and it's "flat" vs. sloped but growing grass wouldn't have the RV value we would need in our northeast climate. we are in all likelihood going with dry cellulose for the crawl space, installed via cutting holes in the roof and then installing vents to protect against moisture, according to an insulation company that specializes in cellulose insulation

what about foam insulation?

ps crawlspace is under house
attic space is between ceiling and roof.
just fyi.

The insulation company told us that foam is fairly toxic so that isn't a great option if you're trying to be green, vs. cellulose which is basically torn up paper (then you have possible dust issues); now, this insulation company just does cellulose so it's not like they offer all options and discuss them with customers, so they would be anti-foam, but still. By crawlspace I meant to say cockloft/attic, in our house the attic space varies depending on location, in some places it's 24" and in others it's 48", since it's on a slope (fairly typical in old brownstones in NYC, I hear), so you can't walk around in there, and have to blow insulation in or use batts. (you can go from the ceiling or the roof to get access)

I'd be curious what other peoples' take is on foam insulation and how "green" it is. By "green" i mean, both non-toxic and also having a good insulation "R" factor so that it actually works.

foam does two things. air seals and insulates.
insulation with air moving through it does little to
insulate. by combining the two, foam is a good product.

as I believe that green is 80% conservation
& 20% everything else..to me it is a green product.

cellulose is ground newspaper with a fire retardant
of borate. and it creates a fine 'dust' that is
borate treated newspaper.

I'm sure others will come along with disadvantages
of foam, so I'll leave that to them.

spray foam (sf) comes in either closed cell, or
open cell. cc is higher R-value. oc is lesser R-value.
R-7 & R-4 depending upon product.

in my hot humid climate..we use open cell.
we know that eventually roofs leak, so we want
a product that allows the moisture to exit.

you'll get biased information from salesmen/women.
even mfg sites, after all they are selling product.
unbiased sites offer better unbiased information.
buildingscience.com
energyvanguard.com
both have info that address foam, insulation types
and climate specific info.

by googling foam..you get lots of info. just
take with a grain of salt mfg info.
and understand that most homeowners have
experience with one job..theirs.

contacting an energy rater in your area would give
you access to companies & products in that area.
the energy rating simplified is a blue print for
efficiency of your specific home. knowing
what leaks, how much it leaks & how to address it
is a great thing.

check with www.resnet.us for energy raters in
your area. we work with both new and existing homes.

and don't insulate until you air seal. things like
recessed lights, attic access, penetrations in ceiling
such as stove vents or bath fan vents should
all be sealed prior to insulation install.

if you have ductwork in the attic space, mastic seal
it prior to insulation. (kinda doubt you do...but just in case.)

best of luck.