Does cellulose insulation off-gas?

Borate-treated cellulose like ours isn't known to off-gas in a normal dry roof. Borate (boric acid and borax) is a stable mineral salt, not a volatile chemical that gases off. The off-gassing stories you'll find online trace to a specific overseas product that used a different, cheaper fire retardant, inorganic ammonium salts (ammonium sulphate), which released ammonia when it got damp. That product was banned. Ours has always used borate, which is exactly the formulation the regulators kept.

It's a story with a twist. European cellulose was treated with borate until 2011, when an EU biocide reclassification capped how much boric acid could be used. To keep meeting fire requirements cheaply, some manufacturers swapped borate out for inorganic ammonium salts (ammonium sulphate). In damp conditions those salts release ammonia (a sharp, cat-pee smell that irritates eyes and airways) and their acidic by-products can corrode copper and wiring. France logged dozens of affected households, banned the ammonium-salt product in June 2013, the EU restricted it Europe-wide in 2016, and France then re-authorised borate as the safer choice. So the additive that caused the trouble was specifically banned; borate was brought back.

The corrosion problem was tied to the ammonium-sulphate retardant. When it got wet it formed acidic by-products that attacked copper, brass and steel nails. Borate is different chemistry: boric acid and borax combined in the standard ratio neutralise each other and are formulated to pass corrosion testing. It's the very reason the all-borate formulation exists. (The honest limit: for a hard, printed corrosion or emissions figure on our exact product we'd point to a lab test, not a blanket promise, but the chemistry and the regulators both came down on the side of borate.)

There are a few, and the key thing is none of them are borate cellulose. 'Chinese drywall' (2005–09) was plasterboard that gave off hydrogen-sulphide gas and corroded copper. Urea-formaldehyde foam (UFFI) in the 1970s off-gassed formaldehyde. Spray polyurethane foam has its own isocyanate-emission concerns. Different products, different chemistry, different makers. Lumping borate cellulose in with them is like saying every car is unsafe because one manufacturer built a bad engine.

Because we make it, in Tiaro, and we've only ever used borate, boric acid and borax, as the fire and pest treatment. It's the same mineral-salt chemistry that regulators kept while banning the ammonium-salt substitute. We can show you the formulation and the safety data sheet, and you're welcome to come and see the factory. We're not a faceless importer; we're the family that pumps it into your roof.