Short answer: Rats and mice don't eat loft insulation for food, but they tunnel through it, pull it apart for nests and soak it with urine, which flattens it and stops it working. No loft insulation is rodent-proof: they will nest in glass wool, stone wool, sheep's wool and loose-fill, and gnaw rigid foam boards. What keeps them out is blocking the way in. After an infestation we refill with standard mineral wool roll to 270mm or deeper.
What Rats and Mice Actually Do to Insulation
- Tunnel through it: runs and tunnels along the routes they use every night.
- Nest in it: pulling it apart and balling it up, often near the eaves or over a warm ceiling.
- Soil it: droppings and urine soak into the fibres and mat them together.
- Flatten it: running and resting on it compresses it.
- Chew what is in it: cables, pipe lagging and anything plastic.
Loft insulation works by trapping still air. Once it is flattened, matted with urine and full of holes, it traps much less heat, and the smell stays in it. That is why soiled insulation is replaced rather than cleaned.
Is Any Insulation Rodent-Proof?
No. Rodents will use whatever is in the loft. Here is how the common types compare:
| Insulation | What rodents do | Worth knowing |
|---|---|---|
| Glass mineral wool roll | Nest and tunnel in it readily | What most UK lofts have; easy to inspect and to replace |
| Stone mineral wool | A little harder to tunnel through, but they still nest in it | Denser and dearer; not rodent-proof |
| Sheep's wool | Nest in it | Natural fibre; more expensive |
| Blown loose-fill | Tunnel through it and scatter it | Harder to clear cleanly if it ever gets soiled |
| Rigid foam boards | Gnaw through edges and existing gaps | Usually fitted between rafters or under boarding |
| Spray foam | Can still be gnawed | Can cause mortgage and survey problems in the UK |
Spray foam is sometimes sold as a fix for rodents. It isn't one, and in the UK spray foam on the underside of a roof can make a house harder to mortgage or sell: several major lenders have said they won't lend on homes with it, and the Royal Institution of Chartered Surveyors published consumer guidance on it in 2023.
What We Refill With After Rodents
We refill with standard mineral wool roll in two layers, one between the joists and a second laid across them, to 270mm or deeper. Typically that is a 100mm layer between the joists and a 170mm layer across the top.
There are good reasons to stick with it after an infestation. Nothing is genuinely rodent-proof, so the refill should be easy to check and easy to replace if they ever get back in. Laying the top layer across the joists also means any new droppings or runs show up on the surface, where you can see them from the hatch. More on how a rodent-damaged loft is cleared and refilled.
What Actually Keeps Them Out
- Close the route. Most rats in lofts come up from a fault in the drains and through the cavity wall; see rats in the walls.
- Seal holes with mesh, not foam alone. Rodents chew through expanding foam. We seal the entry holes we find in the loft with mesh.
- Fit a one-way valve in the drain where the sewer is the route.
- Don't store food up there, including bird seed and pet food.
- Store things in plastic crates, not cardboard boxes, which make good nesting material.
- Cut back ivy and branches touching the walls and roof.
- Look in the loft each autumn, when mice and rats start moving indoors.
Boarded Lofts
In a boarded loft, the insulation under the boards can be soiled even when the boards look clean, because rodents run and nest in the space beneath them. The boards may need lifting to clear it properly. If you are boarding again afterwards, raised loft legs keep the insulation at its full depth under the storage instead of squashing it.
Does Loft Insulation Attract Mice and Rats?
Not by itself. Warmth, shelter and a way in are what draw them. A well-insulated loft is warm and quiet, which makes it more appealing in winter if they can get in, but the answer is no way in, not less insulation. The signs to watch for are in our guides to mice in the loft and identifying droppings.
More Rodent Guides
Everything else we have written about rats and mice in the loft, and the clean-up service itself.
Areas We Cover
Based in Cheshire and working across the UK, with most rodent jobs in Greater Manchester, Merseyside and Cheshire.
Rodents and Loft Insulation FAQs
Do mice eat fibreglass insulation?
No. Mice and rats don't eat loft insulation as food, but they tunnel through it, nest in it and soak it with urine, which ruins it just as surely.
What insulation do rats not like?
None reliably. Dense stone wool is a little harder to tunnel through, but rats and mice will still nest in it. Keeping them out of the loft is what protects the insulation.
Should I fill the holes with expanding foam?
Not on its own, because rodents chew through it. Use steel mesh, held in place with mortar or sealant, for any hole rats or mice could use.
Can I keep some of the old insulation after mice?
Sometimes. If the droppings are confined to one area and the rest of the loft is clean and dry, the soiled section can be cut out and patched. Anything with droppings, urine or nesting in it has to go.
Will new insulation stop rats coming back?
No. New insulation is just new bedding if the way in is still open. The route has to be closed first, then the loft refilled.