Rodent Barrier for Modular Buildings: Installation Timing & Specification

Modular and off-site constructed buildings are delivered as complete structures to a prepared foundation. They may be garden offices, studios, welfare units, modular classrooms, or residential garden rooms — the defining characteristic is that they arrive finished and are craned or rolled into position.

This delivery method creates a specific problem for sub-base protection. Once the module is placed, the ground beneath it is no longer accessible. Any barrier that needs to be installed at ground level beneath the full footprint of the building must be in place before the structure arrives. There is no practical retrofit option for full footprint coverage once a modular building is positioned.

The sub-base void beneath a modular building is often larger than beneath site-built equivalents. The combination of a taller bearer frame, a prefabricated floor cassette, and the clearance required for the delivery process typically leaves a void of 200–400mm beneath the floor — an environment that is attractive to rodents and difficult to seal after the fact.

The correct stage for sub-base barrier installation is during foundation preparation, before the module is craned into position. This is typically the stage at which the ground screws, screw piles, or bearer frame is set. The barrier should be installed immediately after the foundation elements are in place, while the full ground footprint is still open.

For screw pile foundations — the most common foundation type for modular garden buildings — the mesh is positioned flat across the prepared ground between the pile positions, fed around each pile shaft, and lapped at penetration points. The mesh is secured at the perimeter before the building is craned on.

For concrete pad foundations, the mesh is positioned across the pad tops and the soil between them, with the perimeter turn-up against the outer bearer position. See our ground screw rodent protection guide for detailed installation notes on pile-based systems.

The practical challenge with modular sub-base protection is that it sits at the interface between two contractors: the foundation installer and the building supplier. Neither typically includes it as a standard scope item. The foundation contractor installs the piles and leaves. The building supplier delivers and positions the module. The barrier, if it is not specifically specified and supplied, is omitted.

The correct approach is to specify the barrier as part of the foundation preparation programme, supplied and installed before the building is placed. BaseShield™ SubBase Defence can be ordered in advance and installed by the foundation contractor immediately after the piles or pads are set — adding a negligible amount of time to the programme.

For a full explanation of why sub-base protection matters for all raised structures, see our complete prevention guide.

BaseShield™ SubBase Defence is a rolled welded wire mesh barrier — 1m × 25m, covering 25m² per roll — designed for installation beneath raised structures at the foundation stage.

The specification — 7.66mm clear mesh opening, 0.80mm wire diameter, hot-dip galvanised after welding — provides long-term protection in permanent ground-contact conditions. It is designed to last the lifetime of the structure above it without maintenance or inspection.

For modular buildings with footprints of 20–50m², one or two rolls typically provide full coverage. For larger structures, additional rolls are ordered based on footprint area with a 10% addition for overlaps.