I’ve got polystyrene beads or spray foam in my roof. Is it a fire risk?

Be honest with yourself about it: loose expanded-polystyrene beads (the bean-bag type) and many foams are combustible, and that's worth taking seriously. Expanded polystyrene and polyurethane are both foamed plastics, and the Australian Building Codes Board's Fire Safety Verification Method handbook is the document that deals with how foamed plastics are managed for fire under the National Construction Code. Loose EPS beads will catch and can melt and drip as they burn, and rigid or spray polyurethane foam can feed a fire and give off heavy smoke. I won't overstate it. Cured, properly applied foam behaves differently to loose beads or an exposed off-cut, and a lot depends on the product, its thickness and what's around it. But none of it is treated to resist fire spread the way borate-treated cellulose is. If you don't know what's up there or how it was installed, the safe move is to get it looked at by someone who'll tell you straight, and have it removed if it's loose beads sitting around your wiring and downlights.

Loose expanded-polystyrene beads, the kind that spill out of a bean bag, are the version I'd be most wary of in a roof, and people do find them blown in as cheap loose fill. They're a combustible foamed plastic, and foamed plastics are exactly what the ABCB's Fire Safety Verification Method handbook deals with for fire under the National Construction Code. Loose beads have huge surface area, so once they catch they can melt, shrink and drip rather than stay put, and they offer no resistance to a flame moving across them. They also drift down around recessed downlights and old wiring, which is exactly where roof fires tend to start. I'm not trying to frighten you, but if you've got loose beads up there I'd have them assessed, and in most cases removed and replaced with something that's actually treated to resist fire spread, like pumped cellulose.

Spray polyurethane foam is a different animal to loose beads, and the honest answer is: it depends. Polyurethane is a combustible foamed plastic, and foamed plastics are what the ABCB's Fire Safety Verification Method handbook deals with for fire under the National Construction Code, and uncured or exposed foam can ignite and produce dense, dark smoke. Cured foam's behaviour does vary with the product, whether it's open or closed cell, its thickness, and any coating or thermal barrier over it, so I won't tar every foam job with the same brush. What I will say is that no spray foam is treated to resist fire spread the way borate-treated cellulose is. If foam was sprayed straight onto your roof timbers or over wiring without a proper barrier, that's worth a professional fire-safety assessment rather than a guess from the manhole.

Cellulose is recycled paper, so people assume it's the worst of the lot, but it's the opposite, because of the treatment. It's made with borax fire-retardant, and Sustainability Victoria's government guide states that the borax treatment ensures that if the material does ignite, the flame will not spread. So instead of melting and dripping like polystyrene beads, or feeding a fire like exposed foam, borate-treated cellulose chars and glows where a flame touches it, then stops; it's been shown to slow fire spread rather than carry it. Hold a blowtorch to a handful and you can watch it char rather than flare up. I'm not telling you any insulation makes a house fireproof; nothing in your ceiling does that. But of the three that might be sitting in your roof, it's the one I'm most comfortable with around downlights and wiring, and it's the only product I'd use in my own home.

It comes down to what you've actually got and how it was installed, so I'd rather you got it looked at than guessed. Loose polystyrene bean-bag beads blown in as cheap loose fill are the clearest case for removal, they're combustible, they drift around downlights and wiring, and they offer nothing in a fire. Spray foam is more case-by-case: if it was sprayed over a proper barrier and is in good order it may be fine to leave, but if it's exposed against timbers or over wiring it warrants a fire-safety assessment. We vacuum out old insulation as part of our removal service, so if it does need to come out we can clear it cleanly and pump in borate-treated cellulose that's treated to resist fire spread. The first step is an honest set of eyes up there, not a sales pitch, just a straight answer on whether what you've got is a risk.