FAQ · Insulation & rainwater tanks
Fibreglass insulation and tank water: the blanket under a metal roof ends at the gutter line, and nobody has tested swallowing the fibres.
Two different products, two different answers. Ceiling batts lie down in the cavity, away from the water. The foil-faced glasswool blanket under a metal roof runs out to the fascia and finishes on the gutter line, which is exactly where the water leaves your roof. I pull fibres out of gutters regularly. Nobody has ever tested what swallowing them does.
It’s a question I get a lot out on the rural blocks around the South Burnett and the Lockyer, where the house drinks what the roof catches. Here’s where each product actually sits. Batts lie down in the ceiling cavity. The foil-faced anticon blanket runs up under the roof sheets and out to the fascia your gutter hangs off. Then what a normal tank filter does with a glass fibre, and what nobody has ever measured.
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Alstonvale, 2024
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Brisbane
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Brisbane
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Fitzgibbon, 2023
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Upper Caboolture, 2024
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Riverhills, 2023
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Ormeau, 2024
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David H
Sunshine Coast, 2021
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Timea
Highland Park, 2023
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Benjamin H
Carseldine, 2019
“Very good explanation about their works. Advice of existing problems with the roof. Clean work. Very professional.”
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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.”
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Ian G
Burnside, 2019
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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.”
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Danny D
Boondall, 2018
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Pottsville, 2023
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Riverhills, 2018
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Redland Bay, 2023
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West Ipswich, 2018
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Redland Bay, 2017
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Mcdowall, 2017
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Kuluin, 2023
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Brendon
Brays Creek, 2016
“Peter supplied and installed roof insulation for me. He was very informative and provided good advice.”
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Fitzgibbon, 2023
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Trevor G
Brookside Centre, 2016
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Underwood, 2023
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Beaudesert, 2019
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Ashgrove, 2023
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Riverhills, 2018
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Riverhills, 2023
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North Lakes, 2023
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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.”
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Sunshine Coast, 2021
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Cedar Vale, 2021
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Woody Point, 2021
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Jenny C
Plainland, 2021
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Quinton
Coomera, 2020
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Gary P
West Kempsey, 2020
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Batts sit in the cavity. The blanket runs out to the gutter line.
Start with where the water goes. A rainwater tank collects what runs off your roof sheets, into the gutters, down the pipe and into the tank. Ceiling insulation lives away from that run. It sits on top of the plasterboard, down in the cavity, whether it’s fibreglass batts, polyester batts or pumped-in Cellulose Fibre Insulation. The blanket under a metal roof is the different one. It goes in hard under the sheets and the roll runs all the way out to the fascia your gutter is screwed to. So its cut edge finishes at the point every drop of water crosses on its way to your tank.
So the plain answer to “is it safe near my tank?” is that the danger isn’t the material sitting quietly in your ceiling. It’s an open or half-finished roof, a disturbed roof, or a sloppy install that leaves bits of insulation, dust or offcuts lying in the gutters where they don’t belong. That’s a job-quality problem, not a property of the product. Insulation isn’t even a licensed trade in Queensland anymore, so any bloke with a ute and a ladder can call himself an installer, which is exactly why a clean, photographed job matters here more than the badge on the bag.
“Batts sit down in the ceiling, away from the water. The blanket under a metal roof runs out to the fascia and stops on the gutter line. That’s not a bad install. That’s where it’s meant to finish.”Peter Johnson, Comfort Zone Insulation Team
The one under the iron roof
What about the anticon blanket under my iron roof?
Anticon, the foil-faced fibreglass blanket rolled out under the roof sheets during construction, is the one people on tank water ask me about most, and it’s a fair question: unlike ceiling batts, it sits right up under the roofing rather than down in the cavity. Two points worth knowing. First, the rainwater that fills your tank runs across the outside of your roof sheets into the gutter; the anticon is on the underside, so in a sound roof it still isn’t in that water path.
Second, and this is the part worth knowing, anticon is a thin condensation and thermal-break blanket. It is not a substitute for proper ceiling insulation, and it doesn’t give you anywhere near the R-value your ceiling needs in our climate. So if anticon is all you’ve got up there, you still want cellulose pumped into the ceiling to actually keep the house cooler in summer and warmer in winter. Where a fibre worry is legitimate is an ageing, damaged or disturbed blanket shedding fibres that wash into the gutters, and that’s the same catchment-hygiene issue as any roof debris, handled the same way (below). With cellulose in the ceiling, there’s no glass blanket in the picture at all.
Comfort Zone insulation.team
Family-owned insulation manufacturer, making comfy homes since 1986
What’s really in each one
What’s actually in fibreglass, and in cellulose.
I sell all three products, fibreglass included. A batt sale is still a sale for me. Fibreglass batts are made of fine glass fibres held with a binder. They’re the cheapest insulation you can buy, and they do insulate. The fine print worth knowing is the handling side: the manufacturers’ own safety data sheets tell installers to wear a P2 dust mask and to wash work clothes separately, and the Australian Government’s CSIRO notes glass-fibre and rockwool can cause temporary skin, nose and eye irritation. That’s about handling fine glass fibres during the install rather than a batt lying in the ceiling cavity, which is away from the run of water into your tank. The blanket up under the sheets is the one that finishes at the gutter line.
Cellulose is a different beast: it’s made from recycled waste paper, treated with borax and boric acid. No glass fibre, no asbestos, no formaldehyde. The borax is the clever bit. A natural mineral salt that means the insects rats feed on can’t survive in it and has been shown to slow fire spread, and it’s locked into the paper fibre, not floating around loose. The CSIRO describes cellulose as recycled paper combined with fire-retardant chemicals, and notes it’s easy to handle though it can be dusty, so, like any loose-fill, we wear masks when we pump it.
About that borax
Borax is a mineral salt, in the same league as the shaker on your table.
People hear “treated with chemicals” and picture something nasty leaching into their water. Borax is a naturally occurring mineral salt, and it’s about as toxic to you as the common table salt in your kitchen. It’s not asbestos, it’s not formaldehyde, and it’s bound into the paper fibre sitting in your ceiling cavity, not the gutters, and not your tank.
You shouldn’t eat any insulation, the same way you wouldn’t eat the dust and leaf litter off your roof. But plenty of us ate a few pages of a book as kids and lived to tell the tale, and borax is in roughly that league of nasty. Read that as the band it sits in rather than a licence to eat the stuff. And where a product sits matters as much as what it’s made of. Pumped-in Cellulose Fibre Insulation lies down in the ceiling cavity, away from the gutter run. The glasswool blanket is the product that finishes out at the fascia.
Comfort Zone insulation.team
Family-owned insulation manufacturer, making comfy homes since 1986
What actually protects a tank
Clean gutters and a first-flush diverter first, then the question of what’s at the fascia.
If you’re collecting rainwater to drink, start with the cheap things, and they’re the same on any roof. The Australian Government’s yourhome guide to rainwater is good plain reading on this. In practice it comes down to a clean catchment and keeping the ordinary roof grime, dust, leaves, and the droppings from birds, rats and possums, out of the water.
- A first-flush diverter on the downpipe, so the dirtiest first run of water doesn't reach the tank.
- A leaf screen or gutter guard, and gutters kept clear of litter.
- A clean, fully finished roof, with ceiling insulation kept in the cavity and no offcuts or dust left lying in the gutters. On a BAL-rated block being built or re-roofed, ask for the 2 mm corrosion-resistant mesh instead of the glasswool blanket at the fascia.
- A roof cavity that doesn't host vermin, because their droppings are the real thing you don't want washing into a tank.
That last point is where cellulose quietly earns its keep on a tank-water home. Because the insects rats feed on can’t survive in the borax-treated fibre, there’s far less to draw them in , and in my own field experience I’ve pulled rat nests out of plenty of batt-insulated roofs but never out of one we’ve pumped with cellulose. A cleaner cavity means less of exactly the muck you don’t want ending up in your drinking water. The job is done by a Comfort Zone franchise owner-operator who treats your roof like it’s their own. Drop sheets down, work kept in the cavity, site left clean, because they’re building their own reputation in your area. Every job is photographed to the same system and the photos are checked before you’re invoiced, so you can see it was done right, even the bits you’d never climb up to look at.
The practical question
Will a normal water filter take glass fibres out of my tank?
Here’s the detail. Australia’s national standard, written in 1990, put glasswool at a nominal fibre diameter of 5 to 8 microns, with 10 to 20% of fibres finer than 3 microns. That describes the fibre of that era, and nobody has published an equivalent figure for what is made today. The catch is what a micron rating means. Cartridge ratings are set with spherical test particles, so an absolute rating is the largest glass bead that will not pass. A fibre is not a bead: it can sit under the rating across and many times over it long, and a long thin fibre can thread a rated pore end-on instead of being caught side-on. Stepping down from the standard 5 to 20 micron sediment cartridge to a 1-micron absolute cartridge, ultrafiltration or reverse osmosis is the sensible move if it worries you. What nobody can give you is a test: no one has published a trial of a domestic cartridge against glass fibre, so no rating comes with a promise.
NSW Health’s Rainwater Treatment Fact Sheet sets out the same chain. A 20-micron pre-filter, a 1-micron filter before UV, 0.1–0.01 micron ultrafiltration, 0.001 micron reverse osmosis, and makes the point that water filters shouldn’t even be necessary if your catchment and tank are well maintained. In plain terms: a fine sediment filter is a sensible belt-and-braces backstop. But the real fix is upstream. Keep loose fibre off the roof in the first place.
Then there’s the swallowing question. Everything the world knows about glass fibre and health comes from breathing it — lungs, eyes, skin, decades of it. Go looking for the oral side and the shelf is bare. The US Agency for Toxic Substances and Disease Registry’s Toxicological Profile for Synthetic Vitreous Fibers covers glass wool by name and reports no studies located in humans or animals after oral exposure, at any dose, for any effect. No oral limit has ever been set. That profile is from 2004 and nothing has filled the gap since. No study shows harm from drinking it. No study shows it’s safe either. That is the whole of what is known. With pumped-in Cellulose Fibre Insulation the question doesn’t arise: the fibres are paper, and they sit down in the ceiling cavity, not out at the fascia where the water runs.
More on insulation and tank water
Is fibreglass insulation safe near my drinking-water tank?+
Depends which product you mean. Fibreglass batts lie in the ceiling cavity, above the plasterboard and below the roof sheets, away from the run of water into your tank. The foil-faced glasswool blanket under a metal roof is the different one. It runs out to the fascia your gutter hangs off, so its cut edge finishes at the point every drop of water crosses. I find anticon fibres in gutters, most often on recently built or re-roofed houses. Nobody has published a measurement of glass fibre in gutter runoff or tank water, and nobody has tested what swallowing those fibres does. Batts are still made of fine glass fibre, and the manufacturers' own safety data sheets tell installers to wear a P2 dust mask while handling them. Cellulose Fibre Insulation is recycled paper with a borate treatment of boric acid and borax, and it goes in the cavity rather than out at the fascia.
Does ceiling insulation actually touch the water that goes into my tank?+
Ceiling insulation, no. Your tank collects what runs off the roof sheets into the gutters and down the pipe, and that water doesn't pass through the cavity where batts or pumped-in Cellulose Fibre Insulation lie. The product that does sit in the water's way is the glasswool blanket under a metal roof, because the roll runs out past the rafters to the fascia and finishes on the gutter line. That isn't a bad install. That's where it's designed to finish, and on a bushfire-rated block it's often packed into that junction on purpose. Everything else you can get in a tank is ordinary catchment stuff. Leaf litter, roof dust, or a sloppy install leaving offcuts in the gutters. That's why the job is done by a Comfort Zone franchise owner-operator working to one system. Drop sheets down, work kept in the cavity, site cleaned up, and every job photographed with the photos checked before you're invoiced. A first-flush diverter on the downpipe is cheap, sensible insurance on any roof.
What is borax, and is the borax in cellulose a problem for tank water?+
Cellulose is recycled waste paper treated with borax (and boric acid). Borax is a naturally occurring mineral salt, about as toxic to you as common table salt. It's the bit that makes cellulose a place insects won't live in and has been shown to slow fire spread, and it's locked into the paper fibre sitting in your ceiling, not floating around your gutters. Don't go eating the stuff; you shouldn't eat any insulation, the same way you wouldn't eat the dust off your roof. But I will say this: plenty of us ate a few pages of a book as kids and lived to tell the tale, and borax is in roughly that league of nasty. Pumped-in Cellulose Fibre Insulation lies in the ceiling cavity, away from the gutter run. That's the opposite end of the roof from the glasswool blanket, which finishes out at the fascia. If you're worried about anything entering the tank, the answer for any roof is a first-flush diverter and a screened inlet, not picking your insulation around it.
I collect rainwater for drinking, which insulation would you put in my roof?+
After installing insulation since 1986, the pump-in cellulose fibre is the only one I'd use in my own home, tank water or not, and the reasoning holds up here. It's recycled paper and borax rather than fine glass fibre, it pumps in as one seamless blanket with no gaps, it deters the rats and insects whose droppings are the real thing you don't want washing off a roof, and it gives you a far cleaner roof cavity over the decades. If you want batts instead, I'd quote you the polyester, locally made, no glass fibre, over the fibreglass. Whichever you choose, do the cheap things on any tank roof. Clear gutters, a leaf screen, a first-flush diverter and a look in the tank now and then. What that doesn't fix is a glasswool blanket already finishing at your fascia. Short of a re-roof, nothing does. If you're building or re-roofing on a bushfire-rated block, that's the moment to ask for the 2 mm mesh instead.
Will a normal water filter remove glass fibres from my tank water, or do I need a special one?+
Not the cartridge most houses have, and the arithmetic is shakier than either side of this argument admits. Glasswool runs about 5 to 8 microns in nominal fibre diameter. Cartridge micron ratings are set with spherical test particles, so an absolute rating is the largest glass bead that won't pass. A fibre isn't a bead. It can be under the rating across and many times over it long, and a long thin fibre can thread a rated pore end-on instead of being caught side-on. No one has published a test showing what a domestic cartridge does with glass fibre. Stepping down from the standard 5 to 20 micron sediment cartridge to a 1-micron absolute, ultrafiltration or reverse osmosis is the sensible move if it worries you, though nobody can promise 100% at any rating. NSW Health's position is that filters are the backstop and a well-maintained catchment is the main safeguard. With Cellulose Fibre Insulation there's no glass to filter out in the first place.
My roof has anticon blanket under the iron. Is that a problem for my tank, and do I still need ceiling insulation?+
Anticon is a foil-faced glasswool blanket rolled out under the roof sheets. Unlike ceiling batts it sits right up under the roofing, and the roll runs out to the roof edge. It fills the gap at the bottom of the barge cap where the gutter attaches, and it overlaps into the gutter. CSR Bradford's own datasheet says the blanket is ideally suited to sealing ember entry points at ridges, valleys and fascias, so being out at that edge is what it's for. I find anticon fibres in gutters, especially on recently built or re-roofed houses, and wind and heavy rain get straight at that cut edge. What nobody has is a published measurement of glass fibre in gutter runoff or tank water, or a single study on what swallowing those fibres does. On a bushfire-rated block, AS 3959:2018 requires the gaps under the corrugations of a sheet-metal roof to be sealed from BAL-12.5 up, and the blanket is one of three listed ways to do it. Mesh with a maximum 2 mm aperture in corrosion-resistant steel, bronze or aluminium seals the same gap with no glass fibre at the gutter line, so ask for that option if you're building or re-roofing. The other thing to know is that anticon is only a thin condensation and thermal-break blanket. It's not a substitute for proper ceiling insulation and doesn't give you the R-value your ceiling needs in our climate, so even with anticon you still want Cellulose Fibre Insulation pumped into the ceiling.
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On a tank-water block and not sure what to put in? Call Peter on 0414 586 315 , I’ll give you a straight answer for your roof.