Mice Under Sheds: Install a Rodent Barrier for Permanent Protection

Sheds constructed on timber bearers or runners tend to settle over time, creating inconsistent ground contact at the perimeter. Gaps open up at corners and along the length of the bearer — often invisibly from outside — providing entry points that did not exist when the shed was first positioned.

Concrete base slabs are sometimes assumed to eliminate the sub-base risk. They reduce it significantly for burrowing species, but a shed positioned on a slab with a timber perimeter frame still presents a gap at the junction between the frame and the concrete if the seal degrades. Mice will exploit this readily.

Plastic sheds on plastic bases also carry risk. The injection-moulded base panels are designed to drain rather than seal, and the gaps in the floor panel geometry can be sufficient for mouse entry if the shed is positioned over garden soil rather than a sealed surface.

Mouse activity in a shed sub-base is primarily a problem of structural damage and contamination. Timber floor bearers and base frames are gnawed — mice gnaw continuously to keep their incisor teeth at a functional length, and timber is a preferred material. Over time, this weakens the base structure of the shed.

Inside the shed, mice will gnaw through packaging to access food products, shred stored documents, fabric or insulating materials for nesting, and contaminate surfaces and stored goods with urine and droppings. Electrical cabling stored in sheds — extension leads, power tools with cables — is also at risk of gnawing damage.

A mouse infestation in a shed is difficult to resolve once established. Traps and bait will reduce numbers but will not prevent entry if the access point remains open. Identifying and sealing every entry point at the base of an existing shed is time-consuming and frequently incomplete.

Foam fillers and expanding sealants applied to gaps at the base of a shed will be gnawed through by mice within days — they are not a physical barrier in any durable sense. Rubber or brush draught excluders fitted to door thresholds address only that entry point and ignore the perimeter and floor base entirely.

Bait stations placed inside or outside a shed will reduce activity but the fundamental access point — the unprotected gap between the shed base and the ground — remains open. Any reduction in mouse numbers from baiting is temporary if the structure is not physically sealed.

For context on why physical sub-base barriers are the correct approach for all raised structures, see the full guide to preventing rodent access beneath raised structures.

For new shed installations, the correct approach is a sub-base barrier installed flat at ground level across the full footprint of the shed before it is positioned. The barrier must be welded wire mesh with a clear mesh opening of no more than 8mm — sized to prevent mouse entry. The mesh must be hot-dip galvanised to resist corrosion in ground-contact conditions.

The barrier should extend slightly beyond the shed footprint at the perimeter, turned upward against the base frame and fixed in position. This prevents mice from working into the edge junction between the barrier and the shed base. Joins between rolls must be overlapped by a minimum of 100mm and fixed to prevent separation.

For existing sheds where full footprint coverage is not possible, a perimeter barrier — mesh fixed tightly to the base frame and pressed flat into the soil around the full perimeter — provides meaningful reduction in access, though it is not as effective as a full sub-base barrier. Where this approach is used, the junction between the mesh and the shed base must be fixed flush with no gap.