Sub-Base Barrier System: Definition, Specification and Application

A sub-base barrier system is a physical mesh barrier installed at ground level beneath the full footprint of a raised structure, before the structure is built above it. Its purpose is to prevent rodents and other animals from accessing the void between the ground and the underside of the floor.

The term 'sub-base' refers to the layer of ground immediately beneath the floor structure. In the context of raised buildings — garden rooms, modular buildings, decking, sheds on bearers — the sub-base is the soil or prepared ground surface below the bearer frame. A barrier system installed at this level creates a physical exclusion layer that the structure is then built above.

This is distinct from a perimeter seal, a skirting detail, or any treatment applied after construction. A sub-base barrier system is a construction component, specified and installed during the build process, not retrofitted in response to an existing problem.

Any raised structure with an open sub-base creates an accessible void at ground level. That void is sheltered, warm, and undisturbed — conditions that rodents, particularly rats and mice, actively seek out for nesting and harbourage. Without a physical barrier, the void is available for the lifetime of the structure.

Standard construction practice for raised garden structures does not include sub-base protection. There is no building regulation requirement for it in the UK. The sub-base is invisible once construction is complete. And the problem does not announce itself immediately — the gap between construction and the emergence of rodent activity is typically months.

The consequence of an unprotected sub-base is progressive and difficult to resolve once established. Insulation damage, contamination, and the potential for rodents to access the interior of the building through floor junctions all compound over time. Full detail on these consequences is provided in our complete prevention guide.

Welded wire mesh construction. The mesh must be welded — not woven, not hexagonal — to provide consistent aperture geometry and structural rigidity over time.

Clear mesh opening of 8mm or less. Sized to exclude common rodent species including juvenile mice. A 7–8mm clear aperture is the correct specification.

Wire diameter of minimum 0.80mm. Sufficient to resist gnawing from rats and maintain structural integrity in permanent ground contact.

Hot-dip galvanised finish applied after welding. This protects every wire surface and weld point from corrosion. Galvanising applied before welding leaves the weld points unprotected — an important distinction for ground-contact use.

Full footprint coverage. The barrier must cover the full area beneath the structure, not just the perimeter. Perimeter-only installation leaves the full interior of the sub-base void accessible via burrowing beneath the barrier edge.

Correct overlap at joins. Where multiple sections or rolls are used, joins must be overlapped by a minimum of 100mm and fixed to prevent separation over time.

BaseShield™ SubBase Defence is a purpose-built sub-base barrier system in roll format. Specification: 7.66mm clear mesh opening, 0.80mm wire diameter, hot-dip galvanised after welding. Roll size: 1m × 25m (25m² per roll).

It is designed to be installed during the foundation stage of a new raised structure build — before the floor frame is set — and is compatible with all common foundation types: concrete pads, adjustable feet, ground screws, screw piles and bearer frames.

BaseShield is part of the Forti Nova group of construction protection products. It is positioned as a building component — specified by architects, contractors and self-builders at the design stage — not as a reactive pest control measure.