Rats Under Decking: Why a Rodent Barrier is the Only Permanent Solution

The sub-base void beneath a deck is different to that beneath a solid floor structure. The ground beneath the frame is typically undisturbed garden soil — easy to excavate. The deck frame itself provides multiple anchor points for burrowing, and the shaded, humid conditions beneath composite decking in particular create a stable micro-environment throughout the year.

Composite decking is also increasingly sealed at the visible perimeter with fascia boards or edge details, which gives a misleading impression of enclosure. In practice, the sub-base remains fully accessible from the ground beneath the frame because there is no ground-level barrier — only a perimeter face at finished deck height.

Timber decking with a more open frame structure may appear more ventilated, but this also means the sub-base is more accessible. Rats can enter from any angle at ground level, and once established will expand their territory to adjacent structures — including garden rooms, sheds or the main building itself.

Sub-base rat activity beneath decking is rarely visible from the garden surface. The first signs are typically heard rather than seen — scratching or movement beneath the boards, particularly in the evening. Visual evidence at the perimeter — disturbed soil, entrance holes, runs along the base of the frame — may take weeks or months to become apparent.

By the time signs are visible, the problem is established. Reactive treatment at this stage — bait, traps, proofing the perimeter — may reduce activity but cannot prevent re-entry if the sub-base remains open. Without a ground-level barrier, the accessible void remains available to any rat in the vicinity.

Bait stations and traps placed around or beneath the deck address individual animals — not the structural vulnerability. A bait programme will reduce a population, but if the sub-base remains open and the conditions that attracted rats in the first place have not changed, re-colonisation is likely.

Sealing the visible perimeter of a deck with fascia boards or skirting provides no reliable protection. Rats burrow beneath perimeter details without difficulty. Only a ground-level barrier across the full footprint of the structure removes the accessible void. Without it, the sub-base remains available indefinitely.

For a broader explanation of why reactive approaches fail and what an effective sub-base strategy looks like, see the full guide to preventing rodent access beneath raised structures.

A physical sub-base barrier installed flat at ground level across the full footprint of the deck is the correct approach. The barrier must be positioned before the frame is fixed — at the point when the ground beneath the structure is fully accessible.

The product must be welded wire mesh with a clear mesh opening no greater than 8mm. Woven or hexagonal mesh is not suitable — the apertures are inconsistent and distort over time, and common rat species can force through soft or poorly constructed mesh. The mesh must be hot-dip galvanised after welding for adequate corrosion resistance in ground-contact conditions.

The barrier should overlap at all joins by a minimum of 100mm, with joins fixed to prevent separation. At the perimeter, the mesh is turned upward against the frame or bearer to prevent rats exploiting the edge junction. Where the deck frame includes post supports or block footings, the mesh is cut around or lapped close to each contact point.