Buyer’s guide · Underfloor insulation · SE Queensland · 2026
The best underfloor insulation for SE Queensland.
For our humid climate, polyester beats foil beats spray foam under a floor: it won’t trap moisture, lifts back out, suits resale, and costs a fraction. Spray foam is the one I’d never put under a Queensland floor.
I’m Peter Johnson. After 40 years and thousands of SE-QLD subfloors, this is the honest ranking the foam installers won’t print, judged on the things that actually matter under a Queensland house: moisture, resale, removability and cost. Every figure is cited to a real source you can check.
Polyester wins underfloor
vapour-open, non-itch, and it lifts straight back out
The ranking, up front
Polyester, then foil, then foam, for SE QLD.
I'll give you the verdict before the detail, because that's how I'd want it. Here's how the three underfloor options stack up for a raised timber floor in our climate, ranked best to worst.
Polyester batts
RecommendedThe product I'd put under my own floor in this climate.
- Moisture
- Hydrophobic and vapour-open: it won't waterlog and it lets the subfloor breathe.
- Removability & resale
- Stapled up; lifts straight back out in an afternoon and can be reused.
- Cost
- About $28–$35/m² installed, the cheapest of the three.
Foil / reflective (sarking)
SometimesA real role, but only with a clean air gap, and it does little as bulk insulation.
- Moisture
- Foil itself sheds water, but condensation can form on its underside if there's no maintained gap.
- Removability & resale
- Fixed to the framing, more involved to undo than a stapled batt, less permanent than foam.
- Cost
- Cheap per metre, but its R-value collapses towards zero if it's dusty or touching another surface.
Closed-cell spray foam
Not for SE-QLDThe one I'd never put under a Queensland floor.
- Moisture
- Seals the timber airtight (low vapour permeance). In a humid subfloor it can trap damp against the wood.
- Removability & resale
- Permanent. Bonds to joists, pipes and wiring; removal means grinding it off the structure.
- Cost
- Roughly $40–$60+/m², two-to-four times polyester, for the harder option.
That’s the short answer. The rest of this guide explains why our climate decides the order, walks each product honestly, including the one axis where foam genuinely wins, and ends with exactly what we’d put under your floor and why. If you just want the head-to-head on the bottom two, jump to the spray foam vs polyester underfloor comparison.
Why our climate decides the ranking
Under a Queensland floor, moisture is the whole game.
Most “best underfloor insulation” guides you’ll find are national, or worse, written for a cold dry climate on the other side of the world. SE Queensland isn’t that. Our houses sit on stumps over open or enclosed subfloors that breathe humid air half the year, and that single fact reorders the whole ranking. Up north, the question isn’t “which product holds the most R-value per inch.” It’s “which product keeps working in damp air and lets my floor timbers dry out.”
That’s why a material that seals moisture in is the wrong answer here even when its R-rating looks impressive on paper. The Australian Government’s yourhome guide is blunt about it: most insulation “will suffer poor performance and reduced service life if it gets wet,” and a build-up that can’t dry is the documented road to hidden rot and surface mould. So I rank these three the way I’d rank them for your house, not for a brochure, and in our climate that puts the breathable, removable option first and the sealed-in, permanent one last.
“In a humid SE-QLD subfloor, I want the insulation to let the timber dry, not seal the damp in. Get that one thing right and the rest of the decision falls into place.”Peter Johnson, Comfort Zone Insulation Team
A self-supporting polyester batt held firmly between the floor joists, vapour-open, so the subfloor keeps breathing.
The one rule
Under a SE-QLD floor, pick the product that lets your timber dry. That single rule sorts the ranking on its own.
The winner: polyester batts
Polyester is what I’d put under my own floor.
Polyester wins underfloor in SE QLD on every axis a homeowner actually cares about. It’s hydrophobic (it won’t soak up or hold moisture) and it’s vapour-open, so the subfloor keeps breathing and the floor timbers can dry out the way they’re meant to. Pricewise Insulation confirms polyester won’t absorb or retain moisture and keeps performing in humidity, which is exactly the property our climate demands.
It also lifts straight back out. We staple it between the joists, so when a plumber needs at a pipe or a building inspector wants a look at sale time, it comes down in an afternoon and goes straight back up, and it can be reused. It’s a non-itch plastic fibre, inert from day one with no isocyanates and no skin-irritation warning on the bag, and at about $28–$35/m² installed it’s the cheapest of the three as well. The best product for our climate is also the easiest to live with and the kindest on the wallet.
- Hydrophobic & vapour-open, the floor keeps breathing
- Lifts out in an afternoon for access or resale
- Inert from day one: non-itch, no isocyanates
- Cheapest of the three at ~$28–$35/m²
Sometimes: foil / reflective
Foil has a role, but only if you respect the air gap.
Reflective foil and sarking sit second on my list, and I want to be fair about them: they do have a genuine job in some build-ups, working by reflecting radiant heat rather than resisting it like a bulk batt. The trouble is that under a floor, the conditions foil needs to actually work are hard to keep. The Australian Government’s yourhome guide is clear that you must maintain an air space of at least 25mm next to the shiny surface, and that contact with any other building element “will reduce its insulative properties to zero.”
It gets worse with time and dirt. The same government guide notes that dust settling on the reflective surface “greatly reduces its performance,” and that where the foil isn’t kept in the right position its effective R-value “diminishes towards zero” and condensation can form on the underside. A subfloor is dusty, things touch it, and you can’t easily keep a clean 25mm gap under your own house for decades. So foil can be part of a system, but on its own it’s not the reliable underfloor heat insulator a bulk polyester batt is. That’s why it sits ahead of foam but well behind polyester.
The honest read on foil
- Needs a maintained 25mm+ air gap to do anything (yourhome.gov.au).
- Touching another surface drops its value “to zero.”
- Dust on the shiny face “greatly reduces performance.”
- Condensation can form underneath if it’s not positioned right.
Source: Australian Government, yourhome.gov.au (Insulation). Foil is a reflective product, not a bulk insulator; under a floor those conditions are hard to keep.
Not for SE-QLD: closed-cell spray foam
The one I’d never put under a Queensland floor.
Spray foam comes last, and it’s not close. I don’t sell it, so this isn’t “my product versus theirs”. It’s what I’d never do to my own house. Closed-cell foam sets like a hard skin and seals the underside of your floorboards airtight. The Australian Building Codes Board’s Condensation in Buildings Handbook spells out the mechanism: closed-cell insulation has a low vapour permeance, where open materials like mineral wool let moisture through. In a humid SE-QLD subfloor, that sealed skin can trap damp against the timber and drive rot you can’t see.
And once it’s on, it’s on. Foam bonds to the joists, pipes and wiring it’s sprayed over; Australian specialists describe removal as complex, labour-intensive and costly, often needing damaged timbers repaired afterwards. On health, the real risk is the install window: SafeWork NSW lists isocyanates as a leading cause of occupational asthma in Australia, you vacate around 24 hours while it cures, and cheap foam can off-gas VOCs for days, though to be fair, fully cured, well-installed foam is largely inert. Then there’s the price: batts cost about a quarter of spray foam. You pay multiples more for the option that can trap moisture, can’t be lifted out, and carries a real risk while it goes in.
In fairness, foam wins on one thing: a higher R-value per inch. But under a floor you’ve got the full depth of the joist to play with, so we just fit a thicker polyester batt and reach the same total R with no gaps. The one axis foam wins simply doesn’t matter down there.
The bottom line
Here’s what we’d put under your floor, and why.
For a raised timber floor in SE Queensland (a Queenslander, a home on stumps, an old low-set with a suspended floor) we fit polyester batts, cut and friction-fitted snugly between the joists with no gaps. We pick it because it’s vapour-open and hydrophobic so your timber keeps drying, because it lifts out for plumbing access and resale, because it’s inert and non-itch from day one, and because at $28–$35/m² it’s the cheapest of the three as well. The best choice for our climate happens to be the easy one.
And I’ll tell you honestly when a floor isn’t worth doing. The Australian Government’s guidance notes that in some warm-climate homes, insulating a suspended floor can even add a little to summer cooling load, so it’s not an automatic yes. A slab-on-ground house has no subfloor to get into at all. We make our own cellulose in Tiaro, but we won’t pump it under a floor, because a crawlspace is the wrong place for a material that absorbs moisture. It belongs in a sealed ceiling. We fit whichever product is right for the cavity, not whichever one we’d rather sell, which is exactly why you can trust the ranking on this page.
Our pick for SE QLD · 2026
Polyester batts
Fitted snug between the joists, no gaps, to the R-value your NCC climate zone calls for.
- Moisture / resale
- Breathes & lifts out
- Installed cost
- $28–$35/m²
- Vs spray foam
- ¼–½ the cost
Cost bands: Pricewise Insulation (2026). Your quote is fixed to your floor area, access and subfloor condition, not these averages.
Honest answers
Best underfloor insulation: the questions I get asked most.
What is the best underfloor insulation for a SE Queensland home?+
For a raised timber floor in our humid climate, polyester batts are the best choice. They're hydrophobic so they won't waterlog, vapour-open so the subfloor keeps breathing, non-itch to handle, and they lift straight back out if a plumber needs access or you ever sell. They run about $28–$35 per square metre installed (Pricewise Insulation). Foil/reflective has a narrower role and needs a maintained air gap to do anything, and closed-cell spray foam is the one I'd avoid here because it can seal moisture against your floor timbers.
Why is polyester better than spray foam under a floor in Queensland?+
It comes down to moisture. Closed-cell foam has a low vapour permeance. The Australian Building Codes Board's Condensation in Buildings Handbook notes closed-cell insulation seals where open materials like mineral wool let moisture through. Under a SE-QLD house on stumps, that sealed skin can trap damp against the timber and drive rot you can't see or easily remove. Polyester stays vapour-open and hydrophobic, so the floor keeps drying out. Add that polyester lifts out, is inert from day one, and costs a fraction of foam, and the choice is clear for our climate.
Is reflective foil good for underfloor insulation?+
Foil has a real but limited role, and the Australian Government's yourhome guide is honest about it. Reflective foil only works if it keeps a maintained air gap of at least 25mm next to the shiny surface. Contact with another building element reduces its insulating value towards zero, and dust settling on it greatly reduces performance too. Under a floor, where dust and contact are hard to avoid, foil on its own does little as a heat insulator. It can play a part in some build-ups, but for reliable underfloor comfort in SE QLD I'd reach for polyester between the joists.
Does underfloor insulation even work in SE Queensland?+
For a raised timber floor it usually does. It takes the winter chill off the floorboards and helps stop conditioned air leaking away. But I'll be straight with you: the Australian Government's guidance notes that in some warm-climate homes, insulating a suspended floor can actually add a little to summer cooling load. It's worth checking whether your floor is genuinely worth doing rather than assuming it is. A slab-on-ground house has no subfloor to get into, so this isn't for you at all. I'll tell you honestly when I quote.
Can I just use cellulose under my floor?+
No, and we make cellulose, so that's not a sales line. Cellulose is the right product in a ceiling, where it's a seamless, pest-resistant, fire-retardant blanket. But a crawlspace is exposed to ground moisture and humidity, and cellulose is hygroscopic: it absorbs moisture. That's exactly what you don't want against your floor timbers. Under a floor we use polyester, which is hydrophobic and breathes. We fit whichever product is right for the cavity, not whichever one we'd rather sell.
How much should I budget for the best underfloor insulation?+
As a 2026 guide, installed polyester underfloor insulation runs about $28–$35 per square metre, and most whole jobs land in the $1,000–$2,000 range (Pricewise Insulation), depending on floor area, access and subfloor condition. Closed-cell spray foam runs roughly $40–$60+ per square metre. Pricewise Insulation puts batts at about a quarter of the cost of spray foam, so you pay multiples more for the option that can trap moisture and won't lift back out. So the best product for our climate also happens to be the cheapest. Send me your address and I'll work out a fixed price within 48 hours, no deposit.
Want the head-to-head? Read spray foam vs polyester underfloor →
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Send me your address and I’ll work out a fixed underfloor price. Most houses back within 48 hours, no deposit. We fit polyester that won’t trap moisture, lifts out if you ever need it, and costs a fraction of foam. If your floor isn’t worth doing, I’ll tell you that too. Servicing Brisbane & SE QLD.
Peter Johnson
Owner / installer · Comfort Zone Insulation Team® · Since 1986
In the trade and want to install it yourself? We make cellulose in Tiaro and run exclusive territories: franchise with the family.