Do I Need a Rodent Barrier Under a Garden Room?

There are some foundation configurations where a sub-base barrier is less critical. A garden room on a fully solid concrete slab — where the floor structure sits directly on a continuous concrete base with no perimeter gap — does not have a sub-base void to protect. Similarly, a structure with a fully sealed, solid perimeter base (concrete block or brick) that eliminates the ground-level gap may not require a sub-base barrier.

However, these configurations are the minority. Most contemporary garden room construction uses screw piles or adjustable pads specifically because they avoid the need for concrete. These are the configurations that require a barrier.

The most common outcome of an unprotected garden room sub-base is a rodent problem within one to three years of installation. The timeline depends on the rodent population density in the surrounding garden and the proximity of food sources. In gardens with established bird feeders, compost heaps, or neighbouring gardens with rodent activity, the timeline can be much shorter.

When the problem does occur, it is expensive to resolve. Floor insulation must be replaced. Cable damage must be assessed and repaired. Pest control visits are required. And if complete eradication is not achieved — which is common when the access point remains open — the cycle repeats.

The cost of prevention — a barrier installed during construction — is a fraction of the cost of remediation. The disruption of remediation — which in some cases requires the floor structure to be partially dismantled — significantly exceeds anything involved in a 30-minute barrier installation at the build stage.

Not all mesh products are appropriate for sub-base use. The specification that reliably excludes both rats and mice requires: welded wire construction (not hexagonal or woven), a clear mesh opening no greater than 8mm, a wire diameter of at least 0.80mm, and a hot-dip galvanised finish applied after welding. Each of these criteria matters — a product that meets three of four is not adequate.

The barrier must cover the full footprint of the garden room — not just the perimeter. Rodents burrow, and a perimeter-only barrier will be circumvented as animals excavate beneath it and re-enter the sub-base from inside the perimeter. The only approach that works is full-footprint ground-level coverage.

Installation must happen before the floor frame is assembled. Once the garden room is in place, complete footprint coverage is not achievable. Specifying the barrier as a line item in the foundation programme is the correct approach.