Rodents Under Garden Rooms

Most garden rooms are built with an insulated floor. Mineral wool, PIR board or EPS is installed in the floor joist bays — directly above the sub-base void. This insulation is an ideal nesting material. Rats and mice pull it from between the joists and accumulate it in the sub-base, destroying the thermal performance of the floor and creating a substantial nesting mass beneath the building.

Beyond insulation damage, rodents in the sub-base of a habitable garden room present a hygiene concern. Urine and droppings accumulate in the void. Service penetrations through the floor — electrical conduit, plumbing — create potential entry routes into the interior of the building if they are not sealed.

The damage is compounding: a rodent problem that goes unaddressed for six months is significantly harder to resolve than one caught early. And in a garden room used as a home office or studio, the disruption of remediation — potentially including partial dismantling of the floor — is substantial.

Garden room builders work to a specification that covers the structure above ground level. Sub-base protection is not a standard line item. There is no building regulation requiring it for structures of this type. And because the sub-base void is invisible once the build is complete, there is no immediate prompt to address it.

The problem does not announce itself at point of sale. A garden room can look and perform perfectly for months before sub-base activity becomes apparent. By the time the homeowner notices — scratching beneath the floor, disturbed ground at the perimeter, damage to the exterior of the base frame — rodents are already well-established.

This is a structural omission with predictable consequences, not an unpredictable pest event. The correct time to close the sub-base void is before the floor frame is set — not after.

Many garden rooms are finished with a decorative skirting or cladding at the base — composite board, timber battens or a metal trim that conceals the gap between the frame and the ground. This is frequently assumed to provide rodent exclusion. It does not.

Perimeter skirting is installed at the finished ground level. Rodents burrow beneath it. A rat will dig under a skirting panel in hours if there is harbourage on the other side. Mice will find or create a gap at the skirting junction without difficulty.

Skirting provides visual concealment of the sub-base, not physical exclusion from it. A barrier that stops rodent access must be installed at ground level across the full footprint of the structure — not at the perimeter face.

The only reliable long-term approach is a physical sub-base barrier installed flat at ground level before the floor is built. The barrier must cover the full footprint of the structure — not just the perimeter — to prevent burrowing entry from any direction.

The product must be made from welded wire mesh with a clear mesh opening no greater than 8mm. The welded construction is important — hexagonal or woven mesh distorts over time and has inconsistent aperture geometry. Hot-dip galvanised finish is required for corrosion resistance in ground-contact conditions.

Installation timing is critical. Sub-base barrier installation is most effective and most straightforward during the construction phase, before the floor frame is set. Retrofit installation beneath an existing structure is difficult and often results in incomplete coverage. Specifying the barrier during the construction programme adds minimal time and cost compared to the remediation cost of a sub-base rodent problem.

For a complete guide to sub-base barrier specification for raised structures, see the full guide to stopping rodents under raised structures.