How to Stop Animals Getting Under a Shed

Garden sheds and small outbuildings sit on a raised base — typically timber bearers, runners, or paving slabs — with a gap between the floor frame and the ground. That gap is an access point. It does not need to be large. Mice need only 6–7mm. Rats are larger but will excavate beneath a frame if they want access. Cats, foxes and hedgehogs will use wider clearances to shelter beneath the floor.

The conditions beneath a shed are ideal for sheltering animals: dry, dark, undisturbed, and insulated by the floor above. If there are food sources nearby — bird seed, pet food, compost — the attraction increases further. Sheds are typically positioned over garden soil, which is easy to excavate and already home to the invertebrates and insects that small rodents feed on.

The problem is not just that animals are present. Mice and rats cause structural damage — gnawing timber, destroying insulation, contaminating stored goods. Even non-pest species like hedgehogs may need to be considered if a barrier is being installed, since a correctly specified sub-base barrier will also prevent their access.

Mice are the most common species. They can enter through gaps as small as 6–7mm, nest in floor insulation and stored materials, gnaw through packaging and cabling, and establish quickly. Signs include droppings, gnawed materials and nesting debris.

Rats are less common but more damaging. They burrow beneath the shed base, excavate runs and establish nesting territories in the sub-base. Signs include disturbed soil at the perimeter, defined runs along the base of the frame, and larger droppings.

Foxes may use larger clearances — typically 150mm or more — to den beneath outbuildings. They are more likely to use sheds at the end of long gardens with low disturbance. A sub-base barrier will prevent this, though the mesh opening size is less critical than for rodent exclusion.

Each of these cases requires the same fundamental solution: closing the accessible void at ground level.

The most effective approach is a physical sub-base barrier installed at ground level beneath the full footprint of the shed, before the shed is positioned. This removes the accessible void entirely — not just at the visible perimeter, but across the full ground area beneath the floor.

For rodent exclusion, the barrier must be welded wire mesh with a clear opening no greater than 8mm. This is small enough to prevent mouse entry and rat body compression. The material must be hot-dip galvanised after welding for corrosion resistance in permanent ground contact.

For existing sheds that cannot be moved, a perimeter barrier — welded wire mesh secured tightly to the full base frame perimeter and pressed flat into the soil — is the practical alternative. It provides meaningful reduction in access, particularly for larger species, but cannot achieve full footprint exclusion. For complete detail on this approach, see our full prevention guide.

BaseShield™ SubBase Defence is designed for exactly this application. The rolled format (1m × 25m, 25m² per roll) makes it straightforward to install beneath a shed before the building is positioned. For a standard 2.4m × 2.4m shed, a fraction of a roll covers the full footprint.

The 7.66mm mesh opening excludes mice and rats. The 0.80mm wire diameter resists gnawing. The hot-dip galvanised finish is designed for permanent ground contact without corrosion.

For step-by-step instructions, see our installation guide.