Underfloor insulation · Brisbane & SE Queensland
Underfloor insulation that won’t trap moisture under your house.
Under a Queensland floor we fit polyester, not cellulose, not spray foam. It’s hydrophobic, so it shrugs off the damp; it’s non-itch; and it lifts back out if you ever need to get under there. An honest product for an honest job.
Comfort Zone Insulation Team has been crawling through South East Queensland subfloors since 1986. We make our own cellulose for ceilings, but under the floor we use polyester, because it’s the right tool for a damp, open crawlspace. Knowing the difference is the whole point.
Polyester between the joists
snug, non-itch, lifts back out
The short answer
For a Queensland home on stumps, polyester is the right underfloor product: it’s hydrophobic so it won’t waterlog in the humidity, it’s non-itch, it lasts around 20–30 years, and it lifts back out if you ever need to. We don’t pump cellulose under floors (crawlspaces and cellulose don’t mix) and being straight with you about that is exactly why we’re the ones to trust here.
Three products, one right answer
Why polyester under the floor, not cellulose, not spray foam.
I make my own cellulose, and it’s what I’d put in my own ceiling without a second thought. But I will not pump it under your floor, and I want to tell you exactly why. A ceiling cavity is dry and sheltered. A subfloor is the opposite. It’s open to the ground, to the breeze and to the damp that lives under every old Queenslander. Cellulose is hygroscopic, meaning it draws moisture in and releases it again. That’s a feature in a dry roof and a fault under a wet house. Crawlspaces and cellulose don’t mix.
So under the floor we fit polyester batts, the same locally-made, non-itch product some people call the King of batts. Polyester is hydrophobic: it doesn’t absorb or retain moisture, so it keeps performing in our humidity and dries out fast if it ever gets a splash (Pricewise Insulation). It breathes. Spray foam doesn’t.
Here’s the part most installers won’t say out loud: telling you the wrong product would make me money too. I’d rather tell you the right one. That’s the same reason a Brisbane cellulose installer like Roo Roofing openly lists cellulose as “not ideal” for crawl spaces. Even the makers agree it belongs in the roof, not under the floor.
“Telling you to put cellulose under your floor would line my pocket. I make the stuff. I’m telling you to use polyester instead. If I’ll talk myself out of selling my own product, you can trust the rest of what I say.”
What underfloor insulation actually does
A cold floor in winter is the first thing your feet notice.
On a raised timber floor, the ground under your house sucks heat straight out through the boards. In winter the floor is the coldest surface in the room and your heater is fighting it all night. A snug layer of polyester between the joists stops that heat draining away, takes the chill off the floorboards, and quietens the floor while it’s at it.
Warmer floors in winter
Stops heat draining down through the boards into the cold subfloor, so the room your heater is warming actually stays warm.
Hydrophobic, built for our damp
Polyester doesn't soak up moisture, so it keeps working in a humid SE-QLD crawlspace and dries fast if it ever cops a splash.
Non-itch, no SDS warning
It's a plastic fibre, not glass, no itch, no respirator-and-wash-your-clothes-separately fine print. Safe to handle and to live above.
Lifts back out
Plumber needs under the floor? The batts come out and go straight back in. Spray foam is glued on for good.
Lasts ~20–30 years
Polyester doesn't slump or break down the way old fibreglass does. Fit it once and forget it.
Quieter floors
The fill between the joists dampens the hollow drum of footsteps on a suspended floor, a bonus on top of the warmth.
An honest caveat: in a warm climate, underfloor insulation isn’t always a win. The Australian Government’s own guidance notes that insulating a suspended timber floor over an enclosed subfloor can add to the summer cooling load in some homes. We’ll tell you honestly if your floor is worth doing. We’re not here to sell you a job you don’t need.
How we fit it
Snug between the joists, held so it won’t sag.
The batts go up between your floor joists, pressed hard against the underside of the floorboards so there’s no air gap robbing the R-value. We cut them to the bay so they sit snug edge-to-edge. Gaps are where insulation quietly fails, and under a floor nobody ever sees them.
- Friction-fitted as self-supporting batts where the joist spacing allows, so they hold themselves up against the boards.
- Held with stapled straps, galvanised wire or mesh where the bays are wide or the access is awkward, so a batt doesn't droop away from the floor and leave a cold gap.
- Cut tight to every bay, around pipes and bracing, so the floor is covered corner to corner with no short-cuts.
- Kept clear of the perimeter framing so your termite inspector can still read every bearer and pier. We don't bury the timber that needs checking.
Because nothing’s glued down, the whole lot is reversible. That matters more than people realise. One day a plumber or a sparky will need under your house, and with batts they pull a few out and put them straight back.
R-value for our climate
R2.0 to R2.5 is the sensible band for Brisbane.
South East Queensland is NCC Climate Zone 2, a warm, humid zone, not a frozen southern one. Under a floor here, R2.0 to R2.5 does the job: enough to take the cold off the boards in winter and slow the radiant heat in summer, without paying for a higher number this climate doesn’t reward. We size it to your home, not to a sales target.
That’s the same no-overselling philosophy we bring to ceilings, where the NCC minimum for Zone 2 is around R2.5. Buy the rating your climate actually calls for, no more, no less.
Queenslanders & homes on stumps
Built for the classic raised SE-QLD home.
Half the older homes in Ipswich, Logan and the inner-Brisbane suburbs are Queenslanders on timber stumps, exactly the floor underfloor insulation is made for. The trade-off is that those subfloors are also open, breezy and damp, which is precisely why we reach for a hydrophobic polyester batt rather than a moisture-trapping foam.
Tight access, low clearance, old bracing in the way. We’ve crawled through thousands of them since 1986. Now my sons Noah and Eli are part of it, and we’re building a family of franchise partners, other families with the same dedication, running their own businesses to our systems and standards across SE QLD, so it gets done properly the first time.
What it costs
Real SE-QLD install bands, and why the cheap option isn't.
Installed polyester underfloor typically runs about $28–$35 per square metre, with a whole job often landing in the $1,000–$2,000 range depending on floor area, access and the state of your subfloor (Pricewise Insulation). Closed-cell spray foam is roughly $40–$60+ per square metre for the same floor.
So with foam you pay more, up front, for the option that can trap moisture against your timber and doesn’t come back out once it’s cured on. With polyester you pay less for something that breathes, lifts out and lasts. The cheapest-looking job, a badly-done foam, can end up the most expensive thing under your house.
Underfloor, installed
- Polyester batts
- $28–$35/m²
- Closed-cell spray foam
- $40–$60+/m²
- Typical whole job
- $1,000–$2,000
Bands from Pricewise Insulation (2026). Your quote is fixed to your floor area, access and subfloor condition, no day-of surprises.
The one I get asked about every week
“Should I just spray foam the underside instead?”
Plenty of installers will happily foam your subfloor and never mention the catch. Closed-cell foam has a low vapour permeance. It seals the underside of your boards airtight (ABCB Condensation Handbook). In our humid climate that can trap moisture against the timber, which is the documented pathway to hidden rot and mould. And once it’s on, it’s on. Getting it off means grinding it off the joists and risking the structure.
That’s the honest version the foam sellers leave off their websites. I’ve laid out the full comparison (moisture, removability, health during install, and cost) so you can decide with your eyes open.
Pests & inspections
Polyester doesn’t feed anything.
People worry that anything fluffy under the house is a rat hotel. Polyester isn’t. It’s a plastic fibre, not paper or timber, so it’s not a food source for insects or rodents the way some materials are. The real thing to get right under a Queensland home is keeping your subfloor readable for the termite inspector.
So we install with that in mind: batts held back from the perimeter framing, bearers and piers left visible, nothing buried. Your annual pest inspection still works exactly as it should. That’s the opposite of spray foam, which entombs the very timber that needs checking and can hide the early signs of a problem until it’s an expensive one.
Honest answers
Underfloor insulation, the questions I get asked most.
What's the best underfloor insulation for a Queensland home on stumps?+
For a suspended timber floor in South East Queensland's humidity, we use polyester batts. They're hydrophobic, so they shrug off the damp that lives under a Queenslander instead of soaking it up like a sponge. They're non-itch, made in Australia, and they lift back out if you ever need to get under the floor, none of which is true of spray foam glued to your joists.
Why don't you pump cellulose under the floor?+
Because it's the wrong tool for that cavity. Cellulose is brilliant in a dry ceiling, it's what I'd put in my own roof, but a subfloor is open to ground moisture and air, and cellulose is hygroscopic, so it would draw that damp in. Crawlspaces and cellulose don't mix. We use polyester under floors instead, and being honest about that is exactly why you can trust what we tell you about the rest.
What R-value do I need for underfloor insulation in Brisbane?+
For most SE-QLD homes (NCC Climate Zone 2) R2.0 to R2.5 under the floor is the sensible band, enough to take the chill off the floorboards in winter and the radiant cold off in summer, without overspending on a number this climate doesn't reward. We'll tell you honestly if your floor is even worth doing, because in a warm climate underfloor isn't always the win it is down south.
How is underfloor insulation installed under a raised floor?+
The batts sit snugly between the floor joists, hard up against the underside of the floorboards. Depending on the joist spacing and access, they're either friction-fitted as self-supporting batts or held with stapled straps or wire so they don't sag away from the floor. No gaps, no slumping, and nothing glued down. It's reversible by design.
What does underfloor insulation cost in SE Queensland?+
Installed polyester underfloor typically runs about $28–$35 per square metre (Pricewise Insulation), with a whole job often landing in the $1,000–$2,000 range depending on floor area, access and subfloor condition. Closed-cell spray foam is roughly $40–$60+ per square metre for the same job. You pay more for the option that can trap moisture and doesn't come back out once it's cured on.
Will underfloor insulation cause termite or pest problems?+
Polyester doesn't feed anything. It's a plastic fibre, not paper or timber, so it's not a food source for rats or insects. The real watch-point is access for your termite inspector. We keep batts back from the perimeter and don't bury your subfloor framing, so the pest fellow can still read every bearer and pier. Spray foam, by contrast, hides the very timber that needs inspecting.
Want the cold taken off your floors?
Tell us about your home and we’ll give you a fixed-price quote for polyester underfloor insulation (the right product for a SE-QLD home on stumps) usually within 48 hours, with no deposit and no day-of surprises.
Thinking about your ceiling too? That’s where pump-in cellulose earns its keep, and it’s where this all started for our family back in 1986.
In the trade and want to run your own patch? We’re a family business looking for the right people, join the team and come see our Tiaro factory.
Peter Johnson
Owner / installer · Comfort Zone Insulation Team® · Since 1986