Rats in the roof, filmed on the job
Rodent damage in roof insulation — what rats and mice actually do to your batts
I’m Peter Johnson. I’ve been pulling rodent-damaged insulation out of Brisbane roofs since 1986, and it’s the same story in fibreglass batts and polyester batts — rats and mice burrow in, nest, and breed. Here’s what I actually find up there, how fast it happens, and what it takes to fix a roof properly once they’ve moved in.
Rodent damage, Brisbane roofs
what I find pulling old batts out
It’s not the roof, it’s what’s up there
A batt doesn’t bring rodents into your roof. It gives them somewhere to live once they’re in.
Rats and mice get into a roof cavity whether there’s insulation up there or not, through a gap in the eaves, a service penetration, wherever they can find a way in. What decides whether that becomes a five-minute visit or a breeding colony is what they find once they’re inside. A fibreglass batt sitting loose between the joists is exactly what a rodent wants: soft enough to burrow into, hidden enough to nest in, and undisturbed enough to breed in. I’ve filmed the damage this causes over time, and it’s not subtle once you see it.
Rodent damage in old fibreglass batts after years in a roof
Old fibreglass batts show how much damage rodents cause over time, burrowing and nesting right into them.
Read the transcript
Old fibreglass batts and how much damage rodents cause over time — they burrow and nest right in them. All you can do is pull them out and dump them, but the rodent smell stays in the roof. When we pump cellulose fibre in, it disinfects the smell and makes a much better environment. Rodents gnaw power and water pipes too.
That’s old fibreglass batts after rodents have had years to work through them. All you can do with a batt like that is pull it out and dump it, there’s no salvaging it. The rodent smell stays behind in the roof timbers even once the batts are gone, which is exactly why I don’t just put fresh batts straight back in. Pumping in Cellulose Fibre Insulation disinfects that smell and leaves the roof a far better environment than what was up there before.
Being fair about it
Polyester batts are a good product. They’re just not a better product for this.
I install polyester batts and I rate them for plenty of jobs, particularly underfloor and acoustic work. It doesn’t solve the rodent problem though. Polyester is still a soft batt sitting loose between the joists, and a rat or mouse burrows into it, nests in it and breeds in it exactly the same way it does in fibreglass. If someone’s telling you polyester keeps rodents out, that’s not right.
Rodent damage in polyester batts — not much better than fibreglass
Rodent damage in polyester batts isn't much better than fibreglass — batts give rodents a place to live, burrow, nest and breed.
Read the transcript
Rodent damage in polyester batts — not much better than fibreglass. Batts give rodents a place to live, burrow, nest and breed. The damage can happen over 3–4 years or take 20, and it's worse near water, chooks or a nature reserve. It damages the roof, power and plumbing, and the smell attracts snakes.
That’s rodent damage in polyester batts, and it looks the same as what I pull out of fibreglass. A soft batt gives rodents a place to live, burrow, nest and breed, regardless of which fibre it’s made from. Choose polyester for what it’s genuinely good at. Don’t choose it expecting a rodent-proof roof.
There’s no set clock on it
3 to 4 years, or 20. It depends on the house.
I’ve seen serious rodent damage show up in batts within 3 to 4 years of installation, and I’ve seen roofs run 20 years before a colony really gets established. There’s no fixed timeline, it comes down to what’s around the house. A property near a creek or dam, with chooks in the yard, or backing onto bush or a nature reserve gives rodents food and cover close by, so I see worse and faster damage on those blocks than on a house with nothing around it.
That’s worth knowing if you’re deciding whether to check your own roof. A newer house near water or bushland isn’t safe just because the insulation went in recently.
It’s not just the batts
Rodents gnaw pipes and wiring. The smell brings snakes.
The insulation is usually the visible mess, but it’s often not the expensive part. Rodents gnaw on power and water pipes running through the roof space, and I’ve found chewed wiring and split water lines behind what looked, from the manhole, like just a dirty batt job.
The other thing people don’t expect is the smell. Rodent urine and droppings soak into the roof timbers and ceiling sheet over time, and that smell lingers even after the rats are gone. In my experience it’s exactly the kind of smell that draws snakes into a roof looking for an easy feed, so a rodent-infested roof doesn’t stay a rodent problem on its own.
A chewed electrical cable in a roof space, the outer sheath gnawed away and bare wires exposed. This is what I find behind the insulation, not just in it.
Pulled out, disinfected, done properly
Fouled batts get pulled out and dumped. Cellulose Fibre Insulation is what I put back.
Once a batt is burrowed into and fouled, there’s no cleaning it back to usable, it gets pulled out and dumped. That leaves the smell in the roof timbers and sarking, and putting fresh batts straight back in doesn’t deal with that. When I pump Cellulose Fibre Insulation in instead, it disinfects the smell that’s built up in the roof and leaves a far better environment than the one the rodents were living in.
A rat nest matted into chewed polyester batt insulation under a roof eave. Fibreglass or polyester, once it looks like this, it’s going in the skip.
Cellulose Fibre Insulation goes in as a dense, packed blanket rather than a soft loose batt, and it’s treated with boric acid. For the fuller picture on why rodents behave differently around cellulose, including how we back that with a standing reward, read rats in your insulation, the $1,000 Rodent Reward.
Already got fibreglass or polyester batts up there?
Do you have fibreglass batts in your roof now? We can quote to remove them or fix your insulation so the smell and the mess don’t stay for the next thirty years.
Or ask about the $1,000 Rodent Reward
Want the roof pumped with Cellulose Fibre Insulation and want it backed with money, not just a promise? Read the Rodent Reward terms and get a quote.
Keep going
The rest of this guide.
This page covers rodent damage on its own. These cover the rest of the batts decision.
Fibreglass batts — what you’re actually buying
Why fibreglass ended up in nearly every Queensland roof, and what you’re really paying for.
Read the buyer’s guideAre fibreglass batts safe?
Particle size, respirable dust and what the makers’ own safety data sheets actually say.
Read the safety guidePolyester underfloor batts
Where polyester genuinely earns its place, and where it doesn’t solve the problem you think it does.
Read the polyester guideRats in your insulation? The $1,000 Rodent Reward
Why rodents nest in batts and leave dense cellulose alone, backed with a standing reward.
Read the rats FAQFibreglass insulation removal
Old batts fouled, gappy or full of vermin? We’ll quote to remove them and dispose of them properly, or top over them with cellulose.
Removal serviceWhat we actually recommend
Cellulose Fibre Insulation and polyester batts, compared properly.
We install fibreglass batts, Cellulose Fibre Insulation and polyester batts. If you'd rather see the full comparison before deciding, here's where to look.
Recycled paper fibre treated with boric acid, made by us at our own factory in Tiaro. Goes in dense and packed, with no soft layer for rodents to burrow into.
A good product for underfloor and acoustic work. Still a soft batt, so it’s no better than fibreglass against rodents.
Want the full side-by-side across every product we install? Compare cellulose, polyester, fibreglass and foam.
Straight answers
Questions about rodent damage in roof insulation.
How long does it take for rodents to damage roof insulation?+
There's no fixed timeline. I've seen bad rodent damage show up in fibreglass and polyester batts in as little as 3 to 4 years, and I've seen roofs go 20 years before a colony really gets established. It depends on the house, not the calendar. A roof near a creek or dam, near chooks, or backing onto bush or a nature reserve gives rodents food and cover close by, so damage tends to show up faster and worse in those spots than it does on a block with nothing around it.
Do mice and rats damage polyester batts as well as fibreglass batts?+
Yes. Polyester is a genuinely good insulation product, but it's no better than fibreglass when it comes to rodents. Both are soft batts that sit loose between the joists, so a rat or mouse can burrow into either one, build a nest in it, and breed there just as easily. If you're choosing polyester over fibreglass, do it for the reasons polyester is actually better, not because you think it'll keep rodents out.
What do rodents actually do to insulation once they're in the roof?+
They burrow into the batt and nest right in it. A batt doesn't attract rodents in the first place, they get into the roof cavity regardless of what's up there, but once they're in, a soft batt gives them somewhere warm and hidden to live, burrow and breed. That's the difference between a rat passing through and a rat setting up house.
Do rodents in the roof damage anything besides the insulation?+
Yes, and it's often the more expensive part. Rodents gnaw on power and water pipes running through the roof space, which can mean a chewed-through water line dripping into your ceiling or damaged electrical wiring. The insulation is usually the visible mess. What's chewed into the pipes and cabling above it is the part that costs real money to fix.
Why does rodent-damaged insulation smell, and does it attract snakes?+
Rodents living in a batt roof leave urine and droppings behind, and that smell settles into the roof space and lingers. In my experience that smell is exactly what draws snakes in looking for an easy feed, so a rodent-infested roof doesn't just smell bad, it can bring in the next problem behind it.
Can rodent-damaged fibreglass or polyester batts be cleaned, or do they need replacing?+
Once batts are burrowed into and fouled, they can only be pulled out and dumped. There's no cleaning a soiled batt back to a usable state, and the smell stays in the roof timbers and sarking even after the batts are gone. That's the point where I pump in Cellulose Fibre Insulation instead of putting more batts back in. It disinfects the smell in the roof and leaves a far better environment than what was there before.
Had a rodent-damaged roof fixed by us? Tell the next person what came out of it.
A quick honest review genuinely helps a small family business, and helps the next person decide. Thank you.
Fouled batts come out. Cellulose Fibre Insulation goes in clean.
Send us your address and roof type and we’ll give you a fixed-price quote to remove rodent-damaged batts and pump in Australian-made Cellulose Fibre Insulation, no inspection needed.
Peter Johnson
Owner / installer · Comfort Zone Insulation Team® · Since 1986