Before you buy · the independent evidence
Watch these independent videos, and read this, first.
G’day, Peter here from Comfort Zone Insulation Team. We install cellulose and polyester insulation across Brisbane and South-East Queensland, and we get asked about spray foam (spray polyurethane foam, or SPF) all the time. So here’s the straight version, with the receipts. Spray foam can hit a high R-value, no argument. But it’s a two-part chemical reaction finished in your roof, it bonds permanently to your timbers, and the people who inspect roofs for a living (chartered surveyors, government building-safety regulators) have raised real concerns. This page lays out what they’ve actually said and sources every claim. It isn’t a spray on any local installer; it’s a look at the product itself, so you can make your own call.
Watch first
None of these are ours. They’re surveyors, builders and a national broadcaster overseas. They show what spray foam looks like when it goes wrong, and why it’s so hard to undo.
Canada's public broadcaster investigates badly-installed foam that off-gassed and forced homeowners out; install quality is everything.
🇬🇧 UKSkill Builder (UK) documents a real spray-foam roof that caused condensation and mould, ending in a full roof strip, a cautionary case, not a how-to.
🇬🇧 UKA UK chartered-surveying firm shows the defects from an inspector's chair: trapped moisture and timber you can no longer see.
What the evidence says
We’ve kept the language careful on purpose: these are documented risks and mechanisms, what can happen, especially if it’s installed wrong, not a promise about your roof.
A batt or a bag of cellulose arrives at your house already made. Spray foam doesn't. It's two chemicals (Side A is an isocyanate called pMDI; Side B is a blend of polyols, catalysts, a blowing agent and flame retardants) mixed and reacted on-site at the nozzle. The chemistry is completed in your roof, so the install quality is doing a lot of the heavy lifting. The US EPA states the potential for off-gassing of volatile chemicals from spray foam “is not fully understood and is an area where more research is needed.” Get the ratio, temperature or technique wrong and you can be left with unreacted chemicals off-gassing over time. With an inert batt, there's nothing to get wrong that way.
🇺🇸 USSource: US EPA: Health Concerns about Spray Polyurethane Foam ↗
The “A” side chemical, MDI, is one of the leading causes of occupational asthma in Australia. SafeWork NSW classifies it as a respiratory sensitiser and “suspected of causing cancer,” and notes the spray application is the highest-risk process. The US EPA goes further: “there is no recognized safe level of exposure to isocyanates for sensitized individuals.” That's why a professional foam crew suits up in full PPE and air-fed respirators, and why occupants and other trades are told to stay out of the house until the curing period (often ~24 hours) has passed. None of that applies to installing batts or pumped cellulose.
🇦🇺 AUSource: SafeWork NSW: Isocyanates technical fact sheet ↗
This is the big one in a humid SE-QLD climate. Australia's own ABCB Condensation in Buildings Handbook warns that moisture trapped in concealed roof voids causes mould and timber decay that can threaten structural integrity, and that low-vapour-permeance insulation impedes drying. A 2024 UK Government Building Safety Regulator study modelled foam sprayed onto roof tiles as “high risk” of timber decay in every scenario, finding the foam “may create and/or conceal moisture problems.” As surveyors put it, the timber can be dry on its visible face but wet behind the foam, so rot stays hidden until it's advanced. Cellulose and batts leave the roof breathing, so a leak shows itself as a stain. Your early-warning system stays intact.
🇦🇺 AUSource: ABCB: Condensation in Buildings Handbook (NCC 2025) ↗
Batts and loose-fill cellulose can be lifted, topped up, inspected around and removed. Spray foam bonds to your tiles, sheathing, rafters and floorboards. RICS (the global surveyors' standards body) states it directly: “as spray foam is a permanent installation and its removal could potentially damage the existing structure, it is not considered reversible.” Where it's played out overseas, removal means mechanical scraping and grinding and routinely costs more than the original install. (Those are UK experiences, not Australian prices, but they show where a permanent product can lead.) If the substrate won't release cleanly, you're looking at a new roof or floor, not just new insulation.
🇬🇧 UKSource: RICS: Spray foam insulation consumer guide (UK, March 2023) ↗
Foam-covered rafters and sheathing can't be fully inspected. RICS: spray foam “restricts the view from within the roof space; if the timber roof structure is covered with spray foam it cannot be fully seen or inspected.” In termite country, that matters: routine pest, structural and pre-purchase inspections all rely on being able to see the timber. Foam also encases your wiring, plumbing and downlights, so a future leak repair, wiring change or downlight swap can mean cutting through bonded foam. Removable insulation keeps every one of those jobs straightforward.
🇬🇧 UKSource: RICS: Spray foam insulation consumer guidance (UK) ↗
Here's the honest framing: this is a UK situation, not an Australian mortgage rule, and we're not suggesting Australian banks refuse it. But it's worth knowing where unchecked spray-foam roofs have led. A BBC investigation in November 2024 (summarised by the UK Parliament's House of Commons Library) found that a quarter of the UK's biggest mortgage lenders, and all surveyed equity-release lenders, would not lend against homes with spray foam in the roof. The reason is the same building science above: surveyors can't see the timber to confirm it's sound, so the uncertainty itself drives down-valuations. Same physics applies here; the UK is just a few years ahead in finding out.
🇬🇧 UKSource: UK Parliament, House of Commons Library: Spray foam & mortgages ↗
We're not going to tell you spray foam always rots your roof. That's not true, and the sources don't say it. RICS is clear that “as with all types of insulation, poor installation can lead to unintended and adverse consequences.” The fair, defensible point is this: spray foam is a high-stakes product that's easy to get badly wrong (wrong climate, wrong substrate, skipped condensation checks) and near-impossible to reverse if you do. Removable batts and pumped cellulose simply don't carry the irreversibility, the inspection-blocking or the substrate-bonding risk. That's the whole argument.
🇬🇧 UKSource: RICS: Spray foam insulation consumer guidance (UK) ↗
The 30-second test you can do yourself
Expanding polyurethane gap-filler is the same chemical family as spray-foam insulation. Spray a bit onto a timber offcut, let it cure, then try to get it off cleanly. It bonds hard and tears the surface when you scrape it. That’s a hand-scale version of what “removal” looks like across a whole roof or floor. It’s the difference between a product you can pull out and one you can’t.
Do it safely: gloves, good ventilation, no kids or pets nearby. The uncured foam and any smoke are irritants. It’s an analogy to feel for yourself, not a lab test.
The removable, inspectable option
Our position isn’t “never use foam”; it’s that for the vast majority of Brisbane and SE-QLD homes, removable batts and pumped cellulose give you the thermal result without the downsides.
Spray foam vs your safer options
Most spray-foam pages compare foam against a ceiling. But the two places SE-QLD homes most need work are under the floor and in the walls, and that’s exactly where a sealed, low-permeance foam runs hardest against our humid, sub-tropical climate. Here’s the building-physics case, sourced to Australian government and standards bodies, for a removable, breathable product instead. We’re critiquing the method, not any local installer.
A Queensland subfloor is open to the ground, the breeze and the damp. Under there we use a hydrophobic polyester batt. It doesn’t soak up moisture, it breathes, and crucially it lifts back out. We friction-fit or strap it between the joists, cut tight to every bay, and keep it clear of the perimeter framing so your termite inspector can still read every bearer and pier.
Closed-cell foam does the opposite. The ABCB’s Condensation in Buildings Handbook classes closed-cell products as low vapour permeance, they resist drying, while open-cell fibres like polyester are high-permeance and let a damp subfloor breathe. And as Australian engineers Powerhaus put it, sprayed foam “covers everything, including electrical wiring and plumbing… termite inspections are no longer possible,” and “isn’t appropriate in damp areas, as it can stop the flow of water or lock it in.”
“Telling you to put cellulose under your floor would line my pocket. I make the stuff. I’m telling you to use polyester instead.”
A real Comfort Zone underfloor job, self-supporting polyester between the joists, nothing glued, nothing buried.
Brisbane is NCC Climate Zone 2, warm, humid summers. In a wall here, moisture moves both ways across the seasons, and under air-conditioning the summer vapour drive runs inward. A vapour-open batt or blown-in fill keeps buffering and shedding that moisture; a low-permeance foam can sit on the wrong side of the dew point and can’t dry through that face. Whether it matters depends on the wall build-up, which is exactly the question to put to whoever quotes you foam.
The ABCB Condensation Handbook: open-cell fibres like mineral wool typically have high vapour permeance; closed-cell products like polystyrene have low permeance. A breathable fill means moisture isn't trapped against your timber.
🇦🇺 AU
NCC 2025 guidance notes that in warmer, humid climates lower-permeance materials limit inward moisture, but a vapour-closed foam can sit the wrong side of the dew point and can't dry through that face. A breathable fill keeps shedding it.
🇦🇺 AU
yourhome.gov.au notes most insulation underperforms once wet. A vapour-open fill can take up a little incidental moisture and dry again; closed-cell foam gives the timber behind it little path to dry. Keeping water out is the wall's job, but a fill that can dry is more forgiving.
🇦🇺 AU
AS/NZS 3008 derates any cable fully wrapped in insulation, including our own loose-fill, in fairness. The difference is access: you can part a batt to inspect or re-route a cable; foam sets hard around it. (We don't claim foam causes fires.)
🇦🇺 AU
| Consideration (SE-QLD) | Closed-cell spray foam | Polyester underfloor batt | Loose-fill cellulose |
|---|---|---|---|
| Vapour permeance | Low: vapour-closed | High: vapour-open | High: vapour-open |
| Lets a damp subfloor / wall dry | Resists drying | Yes | Yes |
| Removable / serviceable | Bonded: largely irreversible | Lift on the joist & re-fit | Top up / vacuum out |
| Keeps timber & termite barriers inspectable | Coats & conceals | Pull aside to inspect | Part to inspect |
| On-site chemistry / cure lock-out | 2-part reaction; ~24h re-occupancy | Pre-made; none | Pre-made; none (dusty on install) |
| Indicative cost | Job-specific (we don't publish) | ~$28–$35/m² installed | Quoted on measure |
| R-value | High per inch; can drift over 5–10 yrs | Declared to AS/NZS 4859 | Holds when dense-packed |
Permeance is a general material property (ABCB Condensation Handbook); cost bands are third-party (Pricewise Insulation, AU), not a Comfort Zone quote. R-values for any product sold in Australia are declared and tested to AS/NZS 4859.
Some installers market closed-cell foam’s low permeance as an “effective moisture barrier” for humid climates. That’s accurate as far as it goes. Foam does resist vapour. But the ABCB’s Condensation handbook notes that low-permeance layers, while they limit inward moisture, also reduce a wall’s ability to dry. In a climate where vapour is often driven inward, that drying capacity matters. So the same property sold as “sealing moisture out” is the one the condensation literature flags as a drying trade-off, one trait, two ways. Weigh “sealed in” against “able to dry” for your own wall, and get assembly-specific advice.
Don’t take our word for it
Every source we’ve quoted, in full. Australian sources anchor the moisture and chemical argument; the UK and US ones show the mechanism and where it has led.
Honest answers
No. Spray polyurethane foam is a legal, available product in Australia. This page isn't about a ban. It's about giving you the independent evidence (from government building regulators, chartered surveyors and the EPA) on the trade-offs of a permanent, chemically-reactive product, so you can weigh it against removable batts and cellulose for your own home.
We're not aware of any authoritative source showing Australian banks systematically refusing mortgages over spray foam, and we're not claiming they do. The lender-refusal situation is documented in the UK, where a November 2024 BBC investigation (via the House of Commons Library) found a quarter of the biggest lenders won't lend on homes with spray foam in the roof. We flag it only as a 'this is where it's headed overseas' caution. The underlying reason (surveyors can't inspect timber hidden by foam) applies to any roof.
Grab a can of expanding polyurethane gap-filler foam from Bunnings, same chemical family as spray foam insulation. Spray a bit onto a timber offcut, let it cure, then try to get it off cleanly: it bonds hard and tears the surface when you scrape it, a hand-scale version of what removal looks like on a whole roof. Do it safely: gloves, ventilation, no kids or pets nearby; the uncured foam and any smoke are irritants. It's a thirty-second preview of why 'permanent' and 'removable' are the words that matter.
Closed-cell foam does have a high R-value per inch. We won't pretend otherwise. But R-value isn't the only thing that makes a good roof. A correctly installed batt or cellulose system hits the R-value your home needs while keeping the roof breathable, inspectable and reversible. You're trading a bit of thickness for keeping all your options open, and avoiding the moisture, inspection and removal risks the surveyors and government studies have flagged.
They're genuinely different products. Open-cell is lighter, water-blown, breathable, but it can let a leak pass straight through and wet your timber. Closed-cell is dense, rigid, roughly double the R-value per inch, and acts as a vapour barrier, but it can trap moisture against timber that then can't dry out. For a humid SE-QLD roof there's no 'safe' foam type; each fails in a different way. Removable insulation sidesteps both failure modes.
Because they carry none of the irreversible risks. They can be removed and topped up, they don't bond to your structure, they let inspectors see your timber, they keep the roof ventilated the way it was designed, and cellulose is recycled-content, fire-retardant-treated and vacuum-extractable. You get the warmth and the energy savings without locking yourself into a permanent product that the people who inspect roofs for a living have raised real concerns about.
For a Queensland subfloor, open to the ground and the damp, we don't recommend it. Closed-cell foam is low vapour permeance (ABCB Condensation in Buildings Handbook), so it resists drying and can trap moisture against your floor timbers, and once it's sprayed on it can't be lifted out for a plumber or a termite inspection. We fit hydrophobic polyester batts instead: they breathe, they don't soak up the humidity, and they lift back out. Polyester underfloor runs about $28–$35/m² installed versus $40–$60+/m² for foam.
Brisbane is NCC Climate Zone 2, humid summers where, under air-conditioning, the moisture drive runs inward. A vapour-open batt or blown-in fill keeps buffering and shedding that moisture; a low-permeance closed-cell foam can sit on the wrong side of the dew point and can't dry through that face (ABCB Condensation Handbook; NCC 2025). A breathable fill also forgives an incidental leak and lets you part it to re-route a cable, where foam sets hard. Whether foam works depends on the exact wall build-up. Ask whoever quotes you how that wall will dry.
Do the Bunnings test, watch the videos, then give us a call. We’ll tell you straight what we’d put in your roof, your walls or under your floor, and why it can always come back out if you need it to.
