I' planning on blowing cellulose into the attic. I'm concerned about corrosion of the metal plates holding the truss webs together when exposed to the additives in cellulose. Is the ammonium and zinc sulfate something to be concerned about? If so are there other sources of cellulose without the additives? Or how about applying some sort of protectant to the metal plates?

Request borate only treated cellulose. Cellulose used for stabilized damp spray applications would typically be borate only.

http://greenbuildingtalk.com/Forums/tabid/53/aff/14/aft/77306/afv/topic/Default.aspx

http://www.greenbuildingtalk.com/Fo...fault.aspx

The Green Fiber material sold at Lowes and Home depot has sulfate fire retardant They along with most manufacturers have all borate product but it is generally sold to insulation companies not the general public. Where are you located?

Good information. Do you suppose Lowe's or Home Depot can get the borate only? I'm located in Lake Wales, Florida. Thank you for your comments.

I'm going to do an attic upgrade at my daughters in Celebration Fl in April. I'm a celly guy but in this case I'm going to use O.C. fiberglass. Cellulose can have a problem with repeated high temp and high humidity. It's called sublimation. Basically the paper over time turns to dust.

So if I'm reading your correctly I should NOT use cellulose? How long does it take to turn to dust? And when it stabilizes what is the final R-value?

Settling is a function of humidity cycling, not heat, but heat and mold can break down paper fibers over time. Even in FL type heat & humidity cycling it would still take decades to turn to turn to dust. Cellulose from the early 1980s or earlier often had poor manufacturing quality controls, with insufficient additives for suppressing mold growth, and could cook down to junk fairly short amount of time, but they've gotten better about that.

A few years ago on a deep energy retrofit project I was involved with the cellulose in the 2-story balloon framed walls still looked perfect, with no apparent settling when it was gutted for the retrofit. That was 30-35 years after it was installed! But some of the attic cellulose looked like it may have been repeatedly wetted (it was a wreck of a house, mind you), and was starting to look like dust in some corners, but was only dirty, with plenty of loft left in others. Its hard to say what the initial depths and densities were when initially installed, but the attic had poor venting and the humidity cycling may have been extreme.

The labeled R-value of the product is it's fully settled value (if installed per manufacturers' specs), and it will initially outperform that number by a double-digit fraction.

As a DIY it's not insane to use a higher density chunky type fiberglass like AttiCat (available at most box stores) if you can't get decent quality cellulose. Cheap lower density stuff can underperform under hot roof decks, unless you also spring for radiant barrier (one of the most over hyped and underperforming lousy bang/buck type products out there, usually only worth it as a last resort.)

In an air conditioned house in FL it's generally better to go with a sealed attic rather than a vented attic, since the sensible cooling benefits of the venting are small, and the humidity that's introduced to the house can be quite large. Vented attics usually adds more moisture than it removes in a gulf coast climate, and a bad idea everywhere in FL, though often built due to a misplaced or exaggerated belief in the cooling benefits. Put this on your bed-time reading list, and sleep on it:

http://www.fsec.ucf.edu/en/publications/pdf/FSEC-CR-1496-05.pdf

But vented attic or not, air-sealing the attic floor/ceiling plane is a critical first step prior to adding insulation.

http://www.fsec.ucf.edu/en/publications/pdf/FSEC-CR-1496-05.pdf

Good reference, but I don't see anything about "humidity that's introduced to the house" in cases where ducts aren't in the vented attic (where they don't belong). My take-away for FL: "unvented will cost more to build and operate, but provide better hurricane performance".

Painting galvanized steel will certainly improve its corrosion resistance. But I'm not convinced that there is a legitimate concern (other than ocean salt areas).

The way I read it…E1 ventilation saves 5% while E2 sealed saves 8% when ductwork is in attic…negative if ductworks are located elsewhere. E3 the BIG savings to be made is with a reflective white roof. Scientific justification for attic ventilation to control moisture doesn’t seem to exist neither does science support sealed attics for moisture control. It seems to be a horse a piece for roof longevity. Hurricane resistance is best with sealed followed by ridge plus soffit venting. Sealing the attic is expensive.
Back to my Florida remodel; we took out the ductwork in the attic because the electricity bill to run the 3 ton air conditioner was horrendous. The attic was hotter than blazes; no soffit inlets and minimal off-ridge roof vents. We will use a mini-split or window air conditioner to cool the space. With no ductwork in the attic I plan to remove the off-ridge vents (they do let some rain in) and replace with ridge vent and install soffit inlets. BOpt calculations demonstrate we can get by with a 1 ton mini-split once we insulate. I found an installer who will blow in Applegate all borate cellulose for $0.65 per sq. ft. and apply dense pack for $1.25 /sq. ft. to the walls; while waiting for bids for blown in fiberglass. We ripped out the foil that was just under the sheetrock since it was clear that was the cause of water damage along the entire perimeter of the exterior walls.
Thanks for all the good comments!

The same installer should be able to blow fiberglass at a slightly higher cost for the attic.