[Greenbuilding] Cellulose insulation

[Keith Winston]

Hi Lolli,

It will help for you to refine your questions as you learn more.

If you are talking about applying it to the ceiling of your attic, you 
can do it in a ventilated roof assembly if you blow it behind a mesh or 
drywall or something, with a ventilated space behind it (between it and 
the roof sheathing) connected at top and bottom to eave and ridge vents. 
I don't like this style of roof insulating, but it is probably the most 
common. If you dense-pack the cellulose into this assembly, while still 
assuring the ventilation is open, your insulation will probably 
considerably outperform fiberglass as commonly installed in the same 
application.

You shouldn't use cellulose in a cathedral ceiling as a "hot roof" or 
"non-vented roof assembly," since it is not an air barrier. You could 
attempt, in theory, to install it in such a manner in conjunction with 
an air barrier, but it would be ill-advised, I believe.

I think Corwyn assumed you were going to be loose-fill blowing the floor 
of your attic, which would remain a vented attic? In that case, you can 
use the space, but presumeably for storage since it's not conditioned. 
Also, it is not recommended that you have any AC/Heating equipment in 
unconditioned space. Also, the loose-fill cellulose will settle a fair 
bit (dense-pack with settle very little if at all), and will provide 
little or no air barrier (dense-pack is not technically an air barrier, 
but has markedly improved the air tightness of buildings nonetheless).

Also, when loose-filling a floor, it is often difficult to get as much 
insulation as you might like in an existing building, since that floor 
may only be 2x6 construction (or even 2x4 for trusses). You might choose 
to lay down your flooring, perhaps on purlins that give you a better 
depth of insulation, and then dense-pack it under that. You generally 
can't do dense-pack yourself, since it takes more powerful blowers than 
the local building center loans/rents.

Enormous amounts of information about the whys and wherefores is 
available at buildingscience.com.

Warmly, Keith