FAQ · Batts & rivals
Why does my builder recommend fibreglass batts?
Because builders earn a margin on batt supply, batts require no specialist equipment or qualification to install, and no QLD insulation trade qualification has been required since 2003. The recommendation is a business default, not an independent performance review.
That doesn’t make your builder dishonest — it makes them human. But it does mean the choice of insulation product should be yours, made after reading the full comparison between cellulose and fibreglass batts, understanding what the ICANZ 2024 ceiling insulation guidelines say about gaps and real R-value, and knowing why pumped-in cellulose requires equipment a builder doesn’t carry.
The margin question
Builders earn margin on batt supply. That’s standard practice — but worth knowing.
A builder buys batts at trade prices and on-sells them to you at retail. That margin is completely normal in the building industry — it is not fraud, and it is not unique to insulation. Timber, plasterboard, roofing iron: the same model applies to most materials in a build contract.
What it does mean is that the product recommendation has a commercial dimension your builder may not spell out. Fibreglass batts are the default because they are the cheapest and easiest product to spec into a build contract, they arrive in a ute, and every hardware chain sells them. There is nothing stopping a builder specifying pumped cellulose — except that it requires specialist equipment they don’t own, a subcontractor relationship they may not have, and a product they have probably never worked with.
The insulation industry can be confusing, and a lot of the reason is exactly this: since 2003 in QLD there has been no requirement for training to install or sell insulation. That has led to an industry where installers have been doing the job for 10 or 15 years and were never taught how to do it properly. I’ve even read brochures from big companies that misunderstand key concepts and regulations. Learn more about why insulation advice is so confusing.
“I started in this industry in 1986. My father was an insulation contractor before me. I would only ever use cellulose in my own roof — not because I sell it, but because after forty years in roofs it is the only product I’ve never had to go back and fix.”
The qualification gap
No insulation trade qualification has been required in QLD since 2003.
This is the single most important thing to understand about how batts end up in your roof. When the Queensland Building Services Authority (QBSA — now QBCC) removed the insulation trade qualification requirement around 2003, it opened the door to anyone with a ute installing batts with no training and, often, no insurance.
People have died installing insulation since that change. The quieter cost is quality: most batt jobs are done by labourers who have never been taught the right way to install them. I do roof inspections constantly and would say around 80% of the batt jobs I inspect are less than a four out of ten in effectiveness. The gaps are invisible from below. The ceiling looks finished. The bill is paid. And the benefit you paid for has quietly halved.
Pumped cellulose is different not just in product but in the people who install it. You cannot pump cellulose without roughly $60,000 of specialist equipment and the training to use it. That barrier filters out the cut-rate operator. If someone is quoting you pumped cellulose, they have made a real investment in doing the job properly. See also: whether to buy your own batts and have someone else install them.
- No specialist equipment required
- No trade qualification required since 2003
- Cut-to-fit around joists — gaps are inevitable
- Builder can supply and earn margin on product
- ICANZ 2024: 6% gaps roughly halve effective R-value
- Requires ~$60k specialist blowing equipment
- Trained crew required to operate correctly
- Pumped continuous — no cut-to-fit gaps
- Covers joists: no thermal stripes at 450mm centres
- What you order is what ends up in your ceiling
What ICANZ 2024 found — and what the NCC actually requires
Six percent gaps roughly halve the effective R-value. And the NCC only requires R2.5 in SE-QLD.
The ICANZ 2024 ceiling insulation guidelines found that gaps of approximately 6% of the ceiling area roughly halve the effective R-value. That is not 6% of the insulation — it is 6% of the total ceiling left uninsulated. In a cut-to-fit batt job by an untrained installer, 6% gaps are not unusual. Every bay has to be cut. Every pipe, penetration, and corner is a chance for a gap.
So if your builder specifies R3 batts and the installer leaves 6% gaps, you are getting about R1.5 in practice. If they push R5 instead — at higher margin — and the installer leaves the same gaps, you are getting about R2.5. Meanwhile, the NCC requires just R2.5 for Climate Zone 2 (Brisbane and SE-QLD coastal). You may be paying for R5 and getting R2.5, which is exactly what the code requires at the minimum. Learn more about why an R5 batt is not really R5 in your roof.
| Product | Rated R | 6% gaps (ICANZ 2024) | Effective R |
|---|---|---|---|
| Builder-supplied fibreglass batts | R2.5 | ÷ 2 | ≈ R1.3 |
| Builder-supplied fibreglass batts | R3.0 | ÷ 2 | ≈ R1.5 |
| Builder-supplied fibreglass batts | R5.0 | ÷ 2 | ≈ R2.5 |
| Our pumped-in cellulose | R3.0 | No gaps | ≈ R3.0 in the real world |
Source: ICANZ — Ceiling Insulation Guidelines: Existing Homes (2024)
The ceiling accounts for around 25–35% of your home’s heat gain and loss. Getting it right matters. Ceiling insulation that looks done from the manhole but has 6% gaps is not really done.
See what happens when a roof gets hot — and what a proper job looks like.
The first video shows how hot a Queensland roof actually gets in summer. The second is a real review from a customer who switched from a batt spec. The third is a real raked roof job — termites and all — showing what a trained crew handles that a builder’s labourer never would. All three run right here.
Read the transcript
We've just insulated your house — what did you think of the job? I think it's fantastic, I can notice the difference already, which is amazing. So we've got some eggs here, which is not the normal thing, but Ruth has indulged me to cook some eggs on a roof, and I'll hand over to my off-sider to film. So this is the Comfort Zone cooking show now. I'm not a very good cook because I'm a single bloke, but the roof is so hot up there, we'll just see how long it takes to cook an egg. Too hot to touch. Just keep that in there with a bit of bread — there you go, starting to go right on the bottom. I don't know whether this is the best way to cook an egg, but we'll see. If this works, we might just bring eggs along with us — normally some onion, some eggs and some bacon, and we'll have a fry-up on people's roofs. The roof is actually too hot for me to put my hand on. But the eggs were cold when they came out of the box. What's happened is it's actually taken the heat out of where it was sitting — if I had a fry pan up here it would have heated up in the sun, and because the fry pan's thicker on the bottom it would have held the heat. The iron's only a millimetre thick, so I didn't think about that. So I don't think it's working very well. Oh well — it was worth a shot.
Read the transcript
Okay, so I've just hopped into this roof. It's an old roof, and you're always amazed at what you see in old roofs — there's lots of rubbish up here, everywhere. We've gone around and done the downlights; there's a couple of downlights we put the batts around. You'll notice there's some foil over one part of the roof, because they put a new roof on but didn't bother putting the roll blanket on the rest — it's pretty pointless putting it on one part and not the rest, even though it is R1.5. And notice these bits of timber that run from the top down to the bottom — they're actually supporting the roof, so they've been put in afterwards. This roof's in really bad condition, so I've got to be very careful going through here. See the snake skins? That's a new extension up in there, so that looks okay, and we'll get up and pump all of that. But you can see the old tongue-and-groove timbers are all warped and bowing in the middle. They've put a new plaster roof underneath this, so you don't see that from below, but this is all in very bad condition. On the ground there's wasps' nests and everything, and all of this timber is just wrecked. So this is the ceiling — anyway, it's all got a second ceiling under it already, so it doesn't really matter. We'll just pump over the top of it, and that'll keep the termites and things out of it, and we go from there.
The clips play right here on the page, or open the playlist to watch them all on YouTube and subscribe.
Some of these were filmed a while back. Our methods, safety standards and products have moved on since. For how we work today, see the rest of this page.
Some of these were filmed a while back. Our methods, safety standards and products have moved on since then.
More questions about builder insulation recommendations
Does my builder earn money on the batts they specify?
Yes, and that is completely standard practice in the building industry — it is not fraud or a conspiracy. Builders buy batts at trade prices and sell them to you at retail. That margin is how they run a business. What matters is whether you know about it, because it does mean the recommendation is not purely about which product performs best in your roof. The best product for your roof and the best product for your builder’s margin may not be the same thing.
Since when has no insulation qualification been required in QLD?
Since around 2003, when the Queensland Building Services Authority (QBSA — now QBCC) removed the trade qualification requirement for insulation installers. The licence I hold dates from 2006, which is the last year any qualification was required. Since then, anyone with a ute has been able to install batts with no training and often no insurance. This is not just a quality issue — people have died installing insulation because of this change.
Why can’t a builder just pump in cellulose instead of batts?
Because pumped cellulose requires about $60,000 worth of specialist equipment — a blowing machine, hoses, and a trained crew who know how to use them. Builders do not carry that equipment. Batts arrive in a ute, get cut and dropped between joists, and the job is done. There is no specialist gear, no training requirement, and no reason for a builder to change what already fits their workflow and their supplier relationship.
What does the ICANZ 2024 finding mean for a batt job my builder specifies?
The ICANZ 2024 ceiling insulation guidelines found that gaps of around 6% of the ceiling area roughly halve the effective R-value. Builder-laid batts are notorious for gaps — every batt has to be cut to fit around joists, pipes, and penetrations, and the person doing it is usually a labourer with no insulation training. So an R3 batt job with 6% gaps performs at around R1.5 in practice. You’ve paid for R3 and got R1.5.
Does the NCC actually require R5 in SE-QLD?
No. The NCC (National Construction Code) requires R2.5 in Brisbane and coastal SE-QLD (Climate Zone 2). R5 or R6 batts are sometimes pushed by sales reps because the margin is higher on thicker product, not because the code requires it. If your builder or their supplier is quoting you R5 for a new Zone 2 build, it is worth asking why. There are situations where more insulation makes sense, but the NCC minimum for your zone is R2.5.
If my builder has already specified batts, what should I do?
Read the comparison between cellulose and fibreglass batts and decide for yourself. If you want to change the spec, you have the right to do that — the choice of insulation product should be yours, not your builder’s default. If batts are staying, at minimum make sure the installer is trained, the coverage is complete with no gaps, and the R-value being quoted is the actual product R-value, not a total system value (which was made illegal on insulation labels in 2020 but sometimes still appears).
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