Rodents Under Timber Frame: Rodent Barrier Specification & Installation
Timber frame garden structures — from garden offices and rooms to multi-purpose outbuildings — share a common vulnerability: a raised floor on a timber bearer system that creates an open sub-base. Without a specified barrier at the foundation stage, that void is accessible to rodents throughout the lifetime of the build.
How timber frame construction creates sub-base access
A timber frame garden structure is typically constructed on a series of pressure-treated floor joists or bearers supported at intervals by pads, piles, or direct soil contact. The floor deck is then laid over this frame, creating a closed cavity between the underside of the deck and the ground. At the perimeter, the gap between the bottom of the frame and the ground surface is the primary access point.
Even in structures where the bearer frame sits directly on paving or a concrete edging, the junction between the frame and the hard surface is rarely fully sealed. Movement, weathering, and ground settlement create gaps over time. On soft ground, the gap is often continuous around the entire perimeter from day one.
The timber construction itself can become part of the problem. Rodents gnaw timber — both to maintain their incisor teeth and to enlarge access gaps. A sub-base access point that is initially too small for a rat may be gnawed to size within weeks of the structure being installed. The timber bearer frame provides a natural gnaw surface at exactly the right height and position.
The specific risks in a timber frame structure
Once beneath a timber frame structure, rodents gain access to the floor joists and bearers directly. Gnawing on structural timber weakens floor members over time. In severe cases, bearer damage can compromise the structural integrity of the floor deck — though this level of damage typically requires a well-established colony over an extended period.
More immediate concerns are the damage to floor insulation fitted between the joists, contamination of the sub-base void with urine and droppings, and the risk of rodents accessing the structure interior through gaps in the floor deck. In a habitable garden structure — a studio, office, or treatment room — these consequences are operationally significant.
The correct preventive approach
Sub-base protection for a timber frame structure requires a ground-level barrier across the full footprint, installed before the bearer frame is set. The mesh is deployed flat, overlapped at joins, and secured at the perimeter before any superstructure work proceeds.
The specification must include: welded wire construction (not woven or hexagonal), a maximum clear mesh opening of 8mm, and a hot-dip galvanised finish applied after welding. These three criteria together ensure that the mesh physically excludes rodents and performs in permanent ground contact without corrosion failure.
The rolled format of BaseShield™ SubBase Defence is particularly suited to timber frame applications, where the bearer pattern is often irregular and rigid mesh panels would be difficult to fit around the frame geometry. A rolled product can be deployed, adjusted, and lapped around existing pad positions with minimal effort.
The right product for this application
BaseShield™ SubBase Defence is specified as part of the foundation programme for timber frame garden structures. It installs before the bearers are set, requires no specialist tools, and provides permanent sub-base protection for the lifetime of the build.
BaseShield™ SubBase Defence
Forti NovaA purpose-built rolled sub-base barrier system designed specifically to prevent rodent access beneath raised structures. Supplied in 1m × 25m rolls — covering 25m² per roll — with a 7.66mm clear mesh opening and hot-dip galvanised finish applied after welding.
Roll size
1m × 25m
Coverage
25m² per roll
Mesh opening
7.66mm
Construction
Welded wire
Finish
Hot-dip galvanised
Wire diameter
0.80mm
Installation
Lay the BaseShield mesh before setting the bearer frame. Overlap joins by 100mm, fold the perimeter edge upward against the outer frame or foundation, and secure. The bearer frame is then positioned directly over the barrier.
Read the full installation guideFrequently Asked Questions
Stop access beneath your structure
BaseShield™ SubBase Defence is installed during construction to provide permanent sub-base protection. Designed for garden rooms, modular buildings, decking and screw pile foundations.