Fibreglass dust in your house · every number, one page
How much fibreglass dust ends up in your house and how it gets there.
I'm Peter Johnson, a Brisbane insulation contractor since 1986. Batt companies scare people about Cellulose Fibre Insulation being loose in a roof. The measurements run the other way. The industry's own national code puts 10 to 20% of the fibres in glasswool under the 3-micron respirable size, while the US government's own cellulose study found under 0.1% of cellulose fibre by weight comes off as respirable dust. Those are two different measurements — one counts fibres, the other weighs dust — so this page shows the working on both, with the document behind every figure linked beside it.
225–500 kg
of fibreglass into an average roof
Every hole is a hole in both directions
The openings between your roof and your rooms — and there are more of them than a downlight.
Everybody talks about downlights, exhaust fans and range hoods. They are real openings. A downlight cut-out is a hole. A bathroom exhaust fan is a hole with a motor in it. A range hood duct is a hole running straight up over the spot you cook and eat. But that's not the whole list. The rest of it gets skipped every time.
Wiring runs down from the roof space to every light switch and every power point in the house. Each of those is a hole drilled through the top plate for the cable to pass. Where a plasterboard ceiling meets the brickwork in a corner, there's routinely a gap that was never sealed. And behind your fridge, there's a gap that vents fridge heat and, in plenty of kitchens, microwave and cooktop heat straight up into the roof space — with your cooking sitting directly underneath it.
Downlights
A cut hole straight through to the roof space, popped open every time a globe goes.
Exhaust fans & range hoods
A hole with a motor in it or a duct running straight up over where you cook.
Wiring holes
Every light switch and power point has a cable running back up to the roof through a drilled hole.
Corner gaps & the fridge vent
Unsealed gaps against brickwork and the gap behind the fridge that vents straight up — with your cooking underneath it.
Modern LED downlights fix half the problem, not all of it
An IC-4-rated LED downlight runs cool enough to have insulation laid straight over the top, which is a genuine improvement on the old halogen clearance problem. What it doesn't fix is the moment somebody pulls that fitting down to change it or fault-find it. In my own trade experience, next to none of the electricians I see on a roof job are wearing a proper respirator when they do that. If there are fibreglass batts sitting over an IC-4 downlight, that's the moment they're breathing whatever comes down out of the hole with the fitting — and this may matter more for people with asthma, bronchitis or other breathing issues.
A recessed downlight sitting in a plasterboard ceiling. The trim you can see is the lid — on the other side of that hole is the roof space and whatever is loose in it.
A manhole cover being lifted out. It's normally propped wide open the whole time anybody is working up there. It's the biggest hole of the lot.
Every hole above is only a problem because of what’s floating around waiting to come through it. Here’s what that actually looks like the moment a batt gets moved — the loose fibres coming off a batt the instant it’s disturbed, on the other side of every hole above.
Loose fibres floating in the air off a fibreglass batt
Loose fibreglass fibres you can actually see floating in the air the moment a batt gets moved.
Read the transcript
Just pulling out this little bit of fibreglass that somebody hung in here and then decided it was too itchy to insulate their floor with and too hard to get it to hold up. I'm installing this polyester batt and it's quite easy to put in place for a professional installer. But have a look at all of this because you've got to wear really good safety equipment when you use fibreglass because have a look at all the fibres that come out of here. You see that? Yep, all of that fibreglass is itchy. And people say, well why would I bother paying more for the same R value as polyester? You don't have to have this stuff in your home, that's why. I'm not going to touch it any more than that.
A written distance you're supposed to keep off it
"3 metres back" isn't about installers standing apart. It's about anyone in the roof at all.
Clause 6.14(j) of the national code says that where workable, employees not engaged in the work should not be within 3 metres of an overhead synthetic-mineral-fibre work area. It repeats the same distance twice more in its removal schedules. NOHSC:2006(1990) cl 6.14(j), plus Schedule 1 cl 31(a) and Schedule 3 cl 17(a) — search the PDF for “3 metres” ↗ The point isn't that installers work in a crowd. The point is that once fibreglass is installed, the fibres are still up there and still moving every time someone climbs into that roof. Without a respirator, that person is standing well inside 3 metres of them. Particles lift off with any turbulence and float with any disturbance — a pulled batt, a dragged cable, a fan starting up.
On a building site, nobody is allowed within 3 metres during install without proper PPE — the batt companies' own paperwork says as much. Once the job is finished and the ladder's put away, that rule doesn't go with it. The plumber running a new line, the electrician chasing a fault, the antenna installer, the pest man — they're all inside that 3 metres with nothing on. Nobody hands them a copy of the code on the way past. And the gap behind your fridge puts your own cooking within 3 metres of the batts directly above it, where the same code puts 10 to 20% of the fibres under the 3-micron respirable size, every day, with no ladder involved at all.
Who's inside the 3 metres, with nothing on
- Electricians chasing a fault or changing a downlight
- Plumbers running a new line through the roof
- Antenna and solar installers
- Pest control, working through the manhole
- Your own family — under the fridge vent gap, under the bathroom exhaust fan while they're cleaning their teeth in the shower, under an old-style (open) downlight or near a heater flue
All of these spots let the fibres in your roof drift down to where your family breathes. They're invisible — you can't see them coming down. The industry's own national code puts 10 to 20% of the fibres in glasswool batts under the 3-micron respirable size, fine enough to bypass your nose and throat and reach the deep lung. NOHSC:2006(1990), Schedule 3 cl 7 — “The typical proportion of fibres less than 3 µm contained in glasswool materials is in the order of 10 to 20 per cent” ↗
Worth knowing: that's a 1990 code from the old National Occupational Health and Safety Commission. NSW has a public review of it open right now, which is the clearest proof it's still a live document, not a dead one.
You're never far from an opening
Walk through your own house and count how close you actually are to the ceiling.
The National Construction Code sets a 2.4 m minimum ceiling height for most habitable rooms (2.1 m in a kitchen, bathroom or laundry). NCC 2025, Housing Provisions Part 10.3, Clause 10.3.1(1)(a) — “in a habitable room excluding a kitchen — 2.4 m” ↗ Most project-built homes today sit at 2.4 to 2.7 m. So as you walk through the kitchen past the exhaust-fan opening, stand under a downlight or reach past a power point, you're standing a couple of metres at most from a ceiling that has a working hole in it somewhere close by.
Fibreglass also wraps most air-conditioning ducting run through a roof space, unless the ducting has been specified in polyester instead — another surface for loose fibre to sit on and shed from every time the system cycles on.
Constant airflow, not a sealed box
A house isn't a sealed container with air handling bolted onto it — it has constant airflow running through it. That constant airflow is exactly what spreads fine fibres far and wide. They're light enough to move with any draft from a fan, an air-conditioner or an open window. They don't settle the way a heavier dust would. Once a fibre is airborne in that kind of moving air, "where it lands" isn't really the right question — "how long before it moves again" is.
The weight question
A batt job puts 225 to 500 kilograms of fibreglass up above your ceiling.
Work the arithmetic through on an average house and it's a real weight, not an abstract percentage.
- 1An average Australian house is around 150 to 250 square metres of ceiling.
- 2Fibreglass batts weigh roughly 1.5 to 2 kilograms per square metre once laid.
- 3So a full job puts somewhere around 225 to 500 kilograms of fibreglass into the roof.
- 4The industry's own national code puts the typical proportion of fibres under 3 microns — the respirable size — in glasswool materials at 10 to 20%.
- 5That last figure sorts fibres by size rather than weighing them. It says 10 to 20% of the FIBRES in the roof are the respirable size, which is a different statement from 10 to 20% of the weight. It doesn't multiply out to a second kilogram number.
Step 4 is quoted verbatim from the code. NOHSC:2006(1990), Schedule 3 cl 7 — “The typical proportion of fibres less than 3 µm contained in glasswool materials is in the order of 10 to 20 per cent” ↗ Steps 1 and 2 are my own trade figures for an average Queensland job, not a published standard.
So the roof holds hundreds of kilograms of glass, with 10 to 20% of its fibres at the respirable size that reaches the deep lung. The figure that means something to a person isn't either of those. It's what a set of lungs actually takes in.
About 1.3 million glass fibres in a shift
A mask-less installer laying fibreglass batts breathes in roughly 1.3 million respirable glass fibres over an eight-hour shift. That comes off two sourced numbers multiplied together: the 0.14 fibres per cubic centimetre an American field survey measured in the breathing zone of installers laying batts across 107 houses Lees et al. 1993, Applied Occupational and Environmental Hygiene 8(12):1022–1030, via the NTP Report on Carcinogens glass wool profile — “ranged from 0.02 to 0.41 fibers/cm³, with a mean of 0.14 fibers/cm³” ↗ and the 9.6 cubic metres of air a worker breathes in an eight-hour shift at the reference light-work rate of 1.2 cubic metres an hour. ICRP Publication 66 (1994), Human Respiratory Tract Model — Reference Worker light-work breathing rate 1.2 m³/h ↗ Across the measured range that's about 190,000 fibres on a good day and 3.9 million on a bad one. Every fibre in that count is already deep-lung size, since the counting method the survey used throws out anything 3 microns or thicker before it counts at all. NIOSH Manual of Analytical Methods 7400, B counting rules — “Count only fibers ≥5 µm in length … and having a diameter less than 3 µm” ↗
That's an installer's shift. It's also the same air an electrician chasing a fault, a plumber running a line or your own family gets when the roof is disturbed. The fibres don't leave when the installer does. Nobody hands the sparky a respirator on his way past the manhole.
Up to half a tonne of glass fibre sits above your downlights, your exhaust fans and the gap behind your fridge for the life of the house.
Old fibreglass batts pulled back off the ceiling, wiring draped across the top. This is what the kilogram figure is describing — not a single batt, the whole roof's worth.
Working the numbers, not just quoting them
How much boron does an installer actually breathe pumping Cellulose Fibre Insulation?
The fire retardant in our Cellulose Fibre Insulation is boric acid and borax. Both are borates. Both are minerals mined out of the ground like salt. Neither one is sodium or ammonium sulphate. We make the product ourselves at Tiaro, so the recipe is ours to state rather than borrow off somebody else's safety data sheet: the borate treatment runs at about 20% of the finished weight, roughly 12% boric acid and 8% borax.
Boron is only part of each of those. Boric acid is 17.5% elemental boron by mass and borax decahydrate about 11%, straight off the molecular weights. PubChem, Boric acid (H₃BO₃, MW 61.83) — boron 10.81 of 61.83 = 17.5% ↗ PubChem, Borax decahydrate (Na₂B₄O₇·10H₂O, MW 381.4) — 4 × 10.81 of 381.4 ≈ 11% ↗ So 12% × 0.175 plus 8% × 0.11 puts our finished product at about 3% elemental boron by weight. That 3% is the number every line of the arithmetic below runs on.
Boron sits on a chemist's shelf as a bone and joint supplement because a seminal human trial found that 3 mg of boron a day measurably reduced how much calcium and magnesium postmenopausal women were losing in their urine. Nielsen et al., FASEB J 1987;1(5):394-7, PMID 3678698 ↗ The NIH calls that a "might" rather than a settled fact, so I'll call it that too. Nobody's selling fibreglass-dust capsules at the chemist — I asked.
The arithmetic, worked out simply
Worked on respirable dust only — the fraction fine enough to get past a nose and throat and reach the deep lung of somebody wearing no mask. That's the right basis because it's the only fraction a lung actually receives.
- 1. Respirable dust measured in the air on real cellulose jobs: geometric means of 0.11 to 1.53 mg per cubic metre across ten US contractor sites. These are area samples taken in the work space, not samples off a badge clipped to one installer's collar — the report collected 175 personal-breathing-zone samples but published them for total dust only, so this is the closest respirable figure that exists. Individual area readings in the same table run as high as 12.9 mg/m³. NTP TOX-74, Table 15, p.49 — area respirable dust, wet and dry ↗
- 2. × 10 cubic metres of air breathed in an eight-hour shift, the standard occupational-hygiene figure for light-to-moderate work = 1.1 to 15.3 mg of respirable dust for the whole day.
- 3. × 3%, the elemental-boron share of our own Tiaro formulation worked out above (20% borate treatment: 12% boric acid at 17.5% boron plus 8% borax at 11% boron) = about 0.03 to 0.46 mg of elemental boron for the day. That percentage is our recipe rather than a figure lifted off an overseas manufacturer's sheet, which is the whole reason we can print it.
One caveat that belongs beside the answer. The same NTP report found the respirable fraction of cellulose fibre dust is mostly fire retardant rather than paper fibre, so the borate share of what reaches a lung is richer than the 3% product average used above. Nobody has measured how much richer. That makes 3% a floor rather than a ceiling and the modelled range an approximation, which is how it should be read. NTP TOX-74, Abstract p.8 — respirable fractions “consisted mainly of fire retardants” ↗
| A mask-less installer's whole day, modelled from the measured worksite air readings above | 0.03 – 0.46 mg |
| Same model at the US legal respirable-dust limit, 5 mg/m³ all shift | 1.5 mg |
| Blackmores Joint Formula, one tablet, the labelled adult dose | 1 mg/day |
| Blackmores Multivitamin + Antioxidants, one tablet, the labelled adult dose | 2 mg/day |
| TGA threshold above which a supplement must carry a child fertility warning | 3 mg/day |
| Australian recommended daily intake or upper limit for boron | none set |
The two supplement doses are the elemental boron printed on real Australian shelf products. Chemist Warehouse — Blackmores Multivitamin + Antioxidants Sustained Release: “Borax (boron 2 mg) 17.7 mg”, one tablet daily ↗ Chemist Warehouse — Blackmores Joint Formula: “Borax (boron 1 mg) 8.8 mg”, one tablet daily ↗ The 3 mg line is the TGA's, not a nutrition figure: a listed supplement carrying more than 1 mg of boron per daily dose has to warn against giving it to under-2s. More than 3 mg has to warn against under-12s on fertility grounds. TGA — Outcomes: changes to permissible ingredients (low/negligible risk): boron warning statements required above 1 mg and above 3 mg per daily dose ↗ Australia sets no nutrient reference value for boron at all: the NHMRC's own nutrient page for it returns a 404 while iron and the rest resolve, which is the government treating boron as non-essential rather than an oversight. NHMRC / Eat For Health — nutrient page for boron returns “Page not found” ↗ NHMRC / Eat For Health — the index of nutrients that do have reference values ↗ For overseas context only, the US sets a tolerable upper intake level of 20 mg a day and the WHO an acceptable safe range of 1 to 13 mg a day. Neither is an Australian figure. NIH Office of Dietary Supplements, Boron — Health Professional Fact Sheet: WHO acceptable safe range 1–13 mg/day, US adult UL 20 mg/day ↗ The 5 mg/m³ respirable-dust figure is the US OSHA permissible exposure limit quoted in the NTP report, not an Australian workplace exposure standard. NTP TOX-74 — “The OSHA permissible exposure limit (PEL) for PNORs is 15 mg/m3 for total dust and 5 mg/m3 for respirable dust” ↗
So the top of that range, 0.46 mg, is about 23% of the boron in one Blackmores multivitamin tablet — and the bottom of it, 0.03 mg, is under 2% of the same tablet. Australia has no recommended daily intake for boron to measure it against, so the nearest Australian benchmark is the TGA's 3 mg warning threshold. A whole mask-less day of pumping sits at about 15% of that. Even run at the US legal respirable-dust ceiling for a full eight-hour shift, the number tops out at 1.5 mg: under one multivitamin tablet and half the TGA threshold.
That's also an installer's exposure, not a homeowner's, modelled on a full eight-hour shift with no mask at all. In practice most installers spend around two hours actually pumping on a job before moving to the next one, two to three jobs a day, so a real day's dose sits well under even the low end of that range.
Batt companies point at boron toxicity. Here's the actual comparison
Boric acid and borax sit in the same low-acute-toxicity band as ordinary table salt. Salt's oral rat LD50 is 3,000 mg per kilogram, confirmed by two independent manufacturer safety data sheets. Mallinckrodt Baker MSDS, Sodium Chloride ↗ Fisher Scientific MSDS, Sodium Chloride ↗ Boric acid's is 2,660 to 5,140 mg per kilogram and borax's is 3,493 to 6,080 mg per kilogram, per the EPA-cited figures on the US National Pesticide Information Center's fact sheet. NPIC (Oregon State University / EPA), Boric Acid Technical Fact Sheet — “2660-5140 mg boric acid/kg body weight”; “3493 to 6080 mg borax/kg body weight” ↗ So on that single-dose measure both sit in the same low-acute-toxicity band as table salt. Salt's 3,000 mg/kg falls inside the borax range and above the bottom of the boric acid one, which is the point worth making — these are kitchen-shelf numbers, not poison-cabinet ones. Nobody worries about the salt shaker on the kitchen table. A single-dose LD50 says nothing about a daily dose taken for years, which is why the TGA's 3 mg warning threshold above still matters and why the insulation isn't for eating either way.
Both sides, same page
What one shift with no mask on actually puts in you, product by product.
Two columns, both real. How many deep-lung-size fibres you breathe and what chemistry is in the material alongside them. Every figure is worked from a document you can open beside it.
| Product | Fibres breathed in one mask-less 8-hour shift | Chemistry in the material |
|---|---|---|
| Cellulose Fibre Insulation | Effectively none reaching the deep lungUnder 0.1% by weight of it comes off as respirable dust at all. The US government's own study found that fraction is mostly fire retardant rather than fibre. Plant fibre isn't sized or shaped like a glass fibre and doesn't behave like one in a lung. NTP TOX-74, Conclusions — “less than 0.1% by weight was collected as the small respirable particle fraction”; Abstract p.8 — respirable fractions “consisted mainly of fire retardants” ↗ | Boron — no resin, no binderShredded plant fibre with a boric acid and borax treatment, about 3% elemental boron by weight, made at our own factory at Tiaro. A mask-less installer breathes 0.03 to 0.46 mg of boron across a whole shift — less than half the boron in one Blackmores multivitamin tablet, which carries 2 mg. NTP TOX-74, Table 15 p.49 — area respirable dust, modelled to a boron dose in the section above ↗ Chemist Warehouse — Blackmores Multivitamin + Antioxidants: “Borax (boron 2 mg)”, one tablet daily ↗ Boron is a mineral the body already carries and uses. NIH Office of Dietary Supplements, Boron — Health Professional Fact Sheet ↗ No resin, no binder, no formaldehyde. |
| Fibreglass batts | About 1.3 million glass fibresRange about 190,000 to 3.9 million. Worked from a measured mean of 0.14 respirable fibres per cubic centimetre in the installer's breathing zone, multiplied by the 9.6 cubic metres of air breathed in an eight-hour shift. Lees et al. 1993 via NTP RoC — “ranged from 0.02 to 0.41 fibers/cm³, with a mean of 0.14 fibers/cm³” ↗ ICRP Publication 66 — Reference Worker light-work breathing rate 1.2 m³/h × 8 h ↗ | Glass fibre plus a formaldehyde-based binderThe batt and the binder-blown loose fill are both held together with a heat-cured urea-extended phenol-formaldehyde resin at under 15% by weight, CAS 25104-55-6, listed in CSR Bradford's own composition table. CSR Bradford Safe Use Information Sheet, FBS-1 Glasswool, §3 Composition — “Heat-cured resin (fibre binding agent) … <15% … CAS Number 25104-55-6” ↗ Bradford's own website says glasswool products are made with organic binders and therefore contain trace amounts of free formaldehyde, which they describe as measured and very low. CSR Bradford, “Mythbusting insulation and glasswool” — “made with organic binders and therefore contain trace amounts of free formaldehyde” ↗ Formaldehyde is IARC Group 1, carcinogenic to humans. IARC Monographs Volume 100F (2012) — formaldehyde reaffirmed in Group 1, sufficient evidence in humans ↗Keep the two classifications apart because they are not the same substance. The glass fibre itself is IARC Group 3, not classifiable. The Group 1 listing belongs to the formaldehyde in the binder. Knauf markets its ECOSE binder as formaldehyde-free, which is Knauf's own claim about their own product rather than a test I've read. Knauf North America — “without added formaldehyde or dyes”; formaldehyde manufacturing equipment removed from plants (a North America announcement) ↗ |
| Loose-pumped fibreglass, blown with a binder | About 5.3 million glass fibresFrom a measured installer mean of 0.55 respirable fibres per cubic centimetre, roughly four times the batt reading, on the same shift basis. Lees et al. 1993 via NTP RoC — “mean exposures of 0.55 fibers/cm³ for the installer” ↗ | |
| Unbound loose fibreglass, the dustiest job in the study | About 74 million glass fibresRange about 12.7 million to 176.6 million, from an installer mean of 7.67 respirable fibres per cubic centimetre. Lees et al. 1993 via NTP RoC — “ranged from 1.32 to 18.4 fibers/cm³ (mean = 7.67 fibers/cm³) for installers” ↗ | Glass fibre aloneBlown with no binder holding it together, which is the whole reason it reads dustier than anything else in the survey. No resin means no formaldehyde in it. It also means nothing stopping the fibre going where the air goes. Lees et al. 1993 via NTP RoC — “The highest exposures were noted for installation of loose insulation without binder” ↗ |
The three fibreglass fibre counts all come off one field survey of insulation installers across 107 houses in 11 US states, published in 1993 — categories of product, not brands on sale in Australia today. Lees et al. 1993, Applied Occupational and Environmental Hygiene 8(12):1022–1030, as quoted in the NTP Report on Carcinogens glass wool profile ↗ The counting method behind them, NIOSH 7400 B rules, only counts fibres under 3 microns across and longer than 5 microns, so every number in that column is already restricted to deep-lung size. NIOSH Manual of Analytical Methods 7400, B counting rules ↗ Shift volume for all four rows is the same 9.6 cubic metres. ICRP Publication 66 (1994) ↗
What this table does and doesn't prove
The fibre column is a count, not a weight. Nobody has published a milligram-per-cubic-metre dust reading taken during real fibreglass installation — the fibreglass literature counts fibres, so a count is the measurement that exists. The boron milligrams and the fibre counts aren't the same unit either. They shouldn't be. One is a solid particle lodging where the body has no way to shift it. The other is a dose of a mineral that already circulates in you. Read each column for what the product puts into the person standing in it.
On the chemistry side, the two IARC classifications have to stay separate. Glass wool fibre was moved down to Group 3, not classifiable, in 2001. Group 1 is formaldehyde, a component of the binder rather than the fibre. And there's no published toxicological study of the cured binder itself, old formulation or new — Bradford's own safe-use sheet says toxicology test data is generally not available on the products and gives an estimate in place of a measured figure. CSR Bradford SUIS, FBS-1 Glasswool, §11 Toxicological Information — “Toxicology test data is generally not available on the products, but is estimated as being very low” ↗ The boron side has a named human clinical trial behind its dose. Nielsen et al., FASEB J 1987;1(5):394-7, PMID 3678698 ↗
The real numbers, not a rounded-off headline
What the American occupational dust-limit study actually found.
The US National Toxicology Program's worksite survey of ten American cellulose contractors collected 175 personal-breathing-zone total-dust samples. Of those, 26 employees' total-dust eight-hour time-weighted averages exceeded the OSHA permissible exposure limit of 15 mg per cubic metre and 42 exceeded the ACGIH threshold-limit value of 10 mg per cubic metre. NTP TOX-74, Conclusions, p.9 — “26 employees' total dust 8-hour time-weighted averages (TWAs) exceeded the [OSHA] PEL of 15 mg/m³, and 42 exceeded the [ACGIH] threshold-limit value (TLV) of 10 mg/m³” ↗ That's a real, sourced overexposure finding on cellulose fibre worksites. It's why the report's own conclusion says cellulose insulation should continue to be regarded as a nuisance dust and that workers should keep wearing protective masks. That's exactly why my crew wears a Sundström respirator on every job, cellulose fibre or otherwise.
That survey covered cellulose only. I haven't found an equivalent US or Australian field study that measured fibreglass batt or blown-fibreglass installation against those same OSHA and ACGIH total-dust limits, so there's no fibreglass exceedance figure to print alongside it. If a comparable fibreglass survey turns up, I'll put the real number here rather than a guess.
The only fair comparison there actually is
The only way fibreglass matches Cellulose Fibre Insulation on dust is to leave it in the bag.
Every dust reading on this page, from the fibre counts to the kilograms in the roof, is what happens once fibreglass is opened, cut, laid or blown. Sealed in its plastic wrap, it sheds nothing. That's the whole comparison. It's not really one. The moment either product actually does its job, the government's cellulose study puts under 0.1% by weight of cellulose fibre into the respirable range NTP TOX-74, Conclusions — “less than 0.1% by weight was collected as the small respirable particle fraction” ↗ while the national code puts 10 to 20% of the fibres in glasswool under the 3-micron respirable size. NOHSC:2006(1990), Schedule 3 cl 7 ↗
I've pulled an unopened R2.0 batt pack straight out of a roof, still sealed in its wrapper, where a previous installer got paid to lay it and simply left it there instead. It wasn't doing that house any good sitting in the plastic. It also wasn't shedding a gram of dust, which is the only circumstance under which that's true.
Anticon blanket, gutters and rainwater tanks
Does the glasswool blanket under a metal roof end up in the gutter and then in the tank water people drink?
This one splits into what I see, what the manufacturer says and what anybody has actually measured. They're three different things. Mixing them up is how people end up saying something they can't stand behind. The longer version, including the bushfire rules that put the blanket at the gutter line and the toxicology finding on swallowing glass fibre, is on is there glass in your drinking water?
What I see, from forty years on roofs
On plenty of houses the anticon blanket runs right out to the fascia and I can see fibre hanging over the edge into the gutter. The manufacturer's own datasheet says the blanket is ideally suited to sealing ember entry points at ridges, valleys and fascias, so it's meant to be out there. Bradford Anticon blanket datasheet (2014 issue) — “ideally suited to sealing ember entry points at ridges, valleys and fascia's” ↗
What the manufacturer says — and it's fair to print it
CSR Bradford's own safety document states that once installed, the product doesn't release dust or fibres and that binder-coated insulation wool is hydrophobic with no adverse environmental effects expected if it's accidentally released into water or soil. CSR Bradford SUIS, FBS-1 Glasswool, §7 p.3 and §12 p.6 ↗ The blanket is also installed sandwiched under the roof sheet, so in a sound, sealed roof the weather never touches it.
What's actually been measured
I went looking for a water authority test or a published study measuring glass fibre in gutter runoff or tank water and found none. That's the real state of the evidence — the pathway is physically possible on an old roof with torn facing, badly lapped joints or cut edges left open at the eave. That's as far as the documented evidence goes either way.
What I can stand behind is the settling and the filter arithmetic
Glass is heavier than water, so a fibre in a cup does sink. It just sinks unbelievably slowly. A glasswool manufacturer's own safety data sheet puts the true specific gravity of the glass itself at 2.5 to 4.3 grams per cubic centimetre. Asahi Fiber Glass Co., Ltd, Safety Data Sheet “Glass Wool”, SDS-GW-02, §9, p.5 — “Specific Gravity (Density): 2.5-4.3 g/cm3 (true specific gravity) (HSDB 2005)” ↗ That's the density of the glass the fibre is made of, not the bulk density of a batt or a blanket, which is far lower because most of a batt is air.
Run Stokes' law across that whole density range Stokes' law settling velocity — US EPA, Solids Separation module ↗ and a 1-micron fibre takes somewhere between about 15 and 33 hours to fall the ten centimetres to the bottom of a cup. A 3-micron one takes between about 1.7 and 3.7 hours. Stokes' law models a sphere of that diameter, which is how settling is normally worked; a long thin fibre of the same diameter settles somewhat differently, so read these as the order of magnitude rather than a stopwatch. In any real glass, with any warmth or movement in it at all, the fibres look evenly mixed through the water rather than sitting in a layer at the bottom. They do sink — it takes the best part of a day, which in a cup you're about to drink amounts to the same thing.
The filter on your tank almost certainly won't stop it
Puretec's replacement sediment range runs from 0.35 micron up to 250 micron. The cartridges that go into a standard domestic rainwater housing are typically 5 to 20 micron nominal. Puretec replacement sediment cartridge range — ratings of 0.35, 0.5, 1, 5, 10, 20, 25, 30, 50, 60, 100, 150 and 250 micron ↗ A 5 to 20 micron cartridge is between two and twenty times bigger than the fibre. It won't stop it. Puretec do sell finer cartridges — you have to go looking for them and fit one on purpose.
And nominal isn't the same as absolute. A filter manufacturer's own spec sheet defines its micron ratings as 85% or greater removal of a given particle size, so a nominal 1-micron cartridge lets some fraction straight through by definition, not by fault. Pentair/Pentek CBC series cartridge spec sheet, notes ↗
NSW Health's rainwater treatment guide gives the steps that do work: micro and ultrafiltration membranes at 0.1 to 0.01 micron; reverse osmosis at 0.001 micron. NSW Health, Rainwater Treatment Guide, Filtration Treatment Systems section ↗ Drinking off a roof with loose fibre on it calls for that or a 1-micron absolute cartridge at minimum. Get the loose material off the roof edge either way.
Why this bothers me less with our own product
A borate is a mineral your body is already carrying around and already using — the section above covers that. Glass isn't. At the dilution anything off a roof would ever reach a tank, I haven't lost a minute's sleep over borate. That's my own view from forty years on roofs rather than a finding out of a document, so weigh it accordingly.
Straight answers
Fibreglass dust in your house, the questions I get.
Is fibreglass dust actually harmful in a house?+
The industry's own national code puts 10 to 20% of glasswool batt fibre under the 3-micron respirable size — it's fine enough to bypass your nose and throat and reach the deep lung. It's also fine enough to ride moving air rather than settle. Below about 30 microns, particles are governed mainly by airflow rather than gravity and stay suspended for a long time. Fine particles that have already landed get lifted back off a surface by turbulence. Every hardware-store batt pack's own safety data sheet says unprotected exposure to high levels of that dust may cause discomfort of the nose, throat and upper and lower respiratory tract — and this may matter more for people with asthma, bronchitis or other breathing issues. I'm not calling it a carcinogen. IARC moved glasswool down to Group 3, not classifiable, back in 2001. My argument is about where a particle that size ends up once it's airborne in your roof, which is down through every hole in your ceiling rather than staying politely on top of the joists.
How do fibreglass particles get from the roof into the air I breathe?+
Through every hole between your roof space and your rooms — a downlight cut-out, a bathroom exhaust fan, a range hood duct, wiring holes down to light switches and power points, gaps in the corners against the brickwork. Then there's the gap behind the fridge that vents fridge and cooking heat straight up into the roof. Your cooking sits directly under that last one. Warm air moves through a Queensland roof all day. Once a fine fibre is in moving air it travels with the air rather than falling straight down, so it can come back down through any of those openings.
Is there borax in Cellulose Fibre Insulation?+
There is. Boric acid with it as well. Our fire retardant is boric acid and borax. Both are borates. Neither is sodium or ammonium sulphate. It never has been. We make the product ourselves at our own factory in Tiaro, so I can tell you the treatment runs at about 20% of the finished weight: roughly 12% boric acid and 8% borax. Work that back to the metal and the product is about 3% elemental boron. Boron itself sits on a chemist's shelf as a bone and joint supplement, where a Blackmores multivitamin gives you 2 mg of boron a day and their Joint Formula 1 mg. Modelled on the respirable-dust readings measured on ten US cellulose fibre worksites, a mask-less installer breathes about 0.03 to 0.46 mg of boron across a whole day, so the top of that range is about 23% of what's in one multivitamin tablet.
How much fibreglass is actually sitting in an average roof?+
Work the numbers through. An average house is 150 to 250 square metres of ceiling. Fibreglass batts weigh roughly 1.5 to 2 kilograms per square metre once laid, so a full job puts somewhere around 225 to 500 kilograms of glass fibre up above your ceiling. The industry's own national code puts the typical proportion of fibres under 3 microns — the respirable size — in glasswool materials at 10 to 20%. That figure sorts fibres by size rather than weighing them, so it tells you 10 to 20% of the fibres are the respirable size rather than 10 to 20% of the weight. It doesn't give you a second kilogram number. The tangible figure is what a person breathes. A mask-less installer laying batts takes in about 1.3 million respirable glass fibres over an eight-hour shift, which is the 0.14 fibres per cubic centimetre measured on real batt jobs multiplied by the 9.6 cubic metres of air a worker breathes in a shift. So the roof holds hundreds of kilograms of glass with 10 to 20% of its fibres at deep-lung size, sitting above the downlights and exhaust fans for the life of the house.
Does loose-pumped fibreglass make more dust than fibreglass batts?+
A field survey of installers across 107 houses in 11 US states measured the respirable fibre they actually breathed. Laying glasswool batts averaged 0.14 fibres per cubic centimetre, with individual readings from 0.02 to 0.41. Loose fibreglass blown in with a binder averaged 0.55 for the installer, roughly four times the batt figure. The dustiest work in the whole study was unbound loose insulation, where installers averaged 7.67 fibres per cubic centimetre and individual readings ran from 1.32 to 18.4. So yes, loose-pumped fibreglass reads dustier than batts on every measurement I can find, which is exactly why we never blur blow-in fibreglass and pumped Cellulose Fibre Insulation together as the same thing — they are not the same particle, the same size or the same dust reading. That survey was published in 1993 and measured American products, so treat it as the category behaving that way rather than a reading off any particular brand on sale here today.
Can you just leave fibreglass in the pack instead of installing it?+
That's the one way it genuinely matches Cellulose Fibre Insulation for residual inhalable dust — leave it sealed in the bag and don't open it. I've pulled an unopened R2.0 batt pack out of a roof where a previous installer got paid to lay it and didn't. It wasn't doing the house any good sitting there. At least it wasn't shedding dust either. Once it's opened, cut, laid or blown, it starts doing what every dust reading on this page describes.
Figures on this page are read from primary government, standards-body and manufacturer documents, cited beside each claim, current as of July 2026. Safety data sheets get revised — check the current version before relying on it. This page is general information, not medical or occupational-hygiene advice.
Do you have fibreglass batts in your roof now? We can quote to remove them or fix your insulation so there's nothing small enough to be breathed deep into your lungs.
If you'd rather have nothing up there small enough to be breathed deep into your lungs at all — unlike the 10 to 20% of fibreglass batt fibre under the 3-micron respirable size NOHSC:2006(1990), Schedule 3 §7 — “in the order of 10 to 20 per cent” ↗ — the two products that don't have that problem are Cellulose Fibre Insulation (a plant fibre) or polyester batts — get a quote.
Had us sort out old fibreglass for you? Worth a mention.
A quick honest review genuinely helps a small family business, and helps the next person decide. Thank you.
Real reviews, real jobs
What our customers say
Genuine Google & hipages reviews from Comfort Zone customers across SE Queensland.
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Angela M.
SE Queensland
“The fact that I can't even tell it's 6 degrees outside when I wake up in the morning speaks for itself. Have wasted so much money attempting to heat and cool an uninsulated home. Worth every $.”
- Phipages
P Peter
Alstonvale, 2024
“Connected with Comfort Zone Insulation and would recommend them”
- J
Jessa B.
Brisbane
“It dropped about 4 degrees straight away, and we added another 3 with the second job. I appreciate Peter's honesty, and the team showed pictures before and after.”
- Nhipages
Nola M
Birtinya, 2024
“They were courteous and competent.”
- I
Iain V-B.
Brisbane
“Quick and polite service. Great follow-up advice and photos sent for our records. Above and beyond what we expected. Would highly recommend.”
- Jhipages
Jennifer's E
Upper Caboolture, 2024
“Excellent customer service. Highly recommended. Has a profound knowledge of insulation products and has the best interest of his customer.”
- G
Gerry S
Fitzgibbon, 2023
“I used Comfort Zone and they have a done an excellent job.”
- Jhipages
Jennifer
Upper Caboolture, 2024
“Excellent customer service. Highly recommend. Has a profound knowledge of insulation products and has the customer best interest.”
- J
Jung K
Riverhills, 2023
“An experienced family operation. Highly recommend. Thank you for the great job!”
- Dhipages
Diane A
Ormeau, 2024
“Peter and crew did a great job I would definitely recommend them”
- D
David H
Sunshine Coast, 2021
“Completed the job as quoted and to a high standard. Great personal service. Would highly recommend Comfort Zone for ceiling installation work.”
- Thipages
Timea
Highland Park, 2023
“I was extremely satisfied with the service they provided. They gave a very thourough explanation of the materials used, the way the work will be carried out and the price I had to pay was the exact amount quoted, no hidden costs included. They arrived on time, well prepared and workwas carried out exactly how they said it would be, they were super efficient, well prepared and were kind enough to even clean up after themselves. The services they provided was second to none! I don't hesitate to recommend them for any insulation job!”
- B
Benjamin H
Carseldine, 2019
“Very good explanation about their works. Advice of existing problems with the roof. Clean work. Very professional.”
- Mhipages
Mark
Pottsville, 2017
“Michelle, we are done - Peter from comfort zone insulation was very helpful. very honest with his recommendations - in fact he told me that the product my daughter had if installed correctly was superb. Thanks Peter you are a champion and i would recommend you to any person that was wanting professional advice and old school service.”
- I
Ian G
Burnside, 2019
“Good information, communication and professionalism.”
- Jhipages
Jessica
Pottsville, 2016
“This business offers a fantastic product that other businesses did not. Pump in ceiling insulation. Knowledge of the industry second to none.”
- D
Danny D
Boondall, 2018
“He explained everything he was going to do and the different types of insulation they used. He talked through the different options but made a recommendation for the one most people use, which is the one I chose. He was very understanding towards what I needed and not about himself.”
- Jhipages
Jack
Pottsville, 2023
“Excellent communication and informative. Professional.”
- G
Graham R
Riverhills, 2018
“Comfort Zone. Turned up ahead of time, completed in about 2 hours, cleaned up. All good. Very motivated installation team.”
- Thipages
Tony P
Redland Bay, 2023
“Very knowledgeable about insulation”
- A
Alex B
West Ipswich, 2018
“Fast, friendly, efficient.”
- Shipages
Steve
Redland Bay, 2017
“Excellent job and reasonable price.”
- L
Luke D
Mcdowall, 2017
“Peter did a good job. It was a quick and clean service. I'm happy to recommend!”
- Bhipages
Bruce H
Kuluin, 2023
“Prompt and efficient quoting.”
- B
Brendon
Brays Creek, 2016
“Peter supplied and installed roof insulation for me. He was very informative and provided good advice.”
- Ghipages
Gerry S
Fitzgibbon, 2023
“I used Comfort Zone and they have a done an excellent job.”
- T
Trevor G
Brookside Centre, 2016
“Excellent tradesmen from Comfort Zone Insulation. They were punctual and cleaned up after. Highly recommended.”
- Thipages
Tamara
Underwood, 2023
“Peter is honest, hard-working and came on time. Knew excally what he was talking about and answered my questions. Would 100% recommend”
- J
John G
Beaudesert, 2019
“Peter is an honest person who provided me with the information I wanted then performed a good job with great results for the benefit of myself and my family.”
- Shipages
Sterling G
Ashgrove, 2023
“Comfort Zone were very knowledge with great communication and follow up”
- Ghipages
Graham R
Riverhills, 2018
“Comfort Zone. Turned up ahead of time completed in +- 2 hours cleaned. All good. Very motivated installation team”
- Jhipages
Jung K
Riverhills, 2023
“An experienced family operation. Highly recommend. Thank you for the great job!”
- Khipages
Kathy A
North Lakes, 2023
“We connected with Peter through HiPages and he was prompt, professional and even came back after the job was complete to assist with a question we had. We would highly recommend Peter for further insulation works.”
- Dhipages
David H
Sunshine Coast, 2021
“Completed the job as quoted and to a high standard. Great personal service. Would highly recommend Comfort Zone for ceiling installationn work.”
- Shipages
Sue H
Sunshine Coast, 2021
“Incredible customer service”
- Ehipages
Eileen C
Cedar Vale, 2021
“Quality work, good customer service, prompt”
- Chipages
Craig M
Woody Point, 2021
“Called within 5 minutes of request. Very knowledgeable and explained job in great detail, provide great advice in prior preparation for works required. Very friendly and helpful.”
- Jhipages
Jenny C
Plainland, 2021
“Although I did not hire Peter I was impressed with the initial contact and the knowledge he was willing to impart. I was treated with respect which I appreciated. I would have hired but I received a lower quote.”
- Qhipages
Quinton
Coomera, 2020
“Professional installation without any short cuts. True to their word with high integrity. Response from Comfort Zone Insulation”
- Ghipages
Gary P
West Kempsey, 2020
“Came & Gave a free quote”
Get the loose particles sorted, not just the R-value.
Send us your address and roof type for a fixed-price quote within 48 hours for most houses — removing old fibreglass, topping over it safely or pumping Cellulose Fibre Insulation or polyester from scratch. Servicing Brisbane, SE QLD and Northern NSW.
Peter Johnson
Owner / installer · Comfort Zone Insulation Team® · Since 1986