Rodents Under Raised Extension

Once an extension is complete, the sub-base void is enclosed above by the floor deck and bounded on at least one side by the existing building. Retrofitting a barrier in this environment is significantly more difficult than in a freestanding garden structure — access is restricted, ground conditions may vary considerably within the footprint, and there is no clear perimeter edge to fold the mesh against.

The only practical solution is to specify the barrier at the groundworks stage — before the piles are loaded, before the bearer frame is set, and before any superstructure work begins. At that point, the full footprint is accessible, the ground is relatively clear, and installation is straightforward.

The specification for a raised extension sub-base barrier is the same as for any other raised structure: welded wire mesh with a maximum 8mm clear mesh opening, hot-dip galvanised after welding, covering the full footprint. The key additional consideration for extension applications is the junction with the existing building — the mesh should be overlapped against the existing damp proof course level and sealed at the junction to prevent rodents accessing the gap between old and new construction.

Where the extension footprint is larger than a standard garden building, multiple rolls are required with 100mm overlaps at joins. The barrier must be continuous — any gap, however small, is a potential access route. Perimeter edges should be folded upward against the pile caps or perimeter frame to prevent rodents exploiting the edge junction.