Squirrels Under Decking
Grey squirrels are a commonly overlooked cause of sub-base damage beneath raised garden decking. Larger than mice and considerably more destructive than rats when it comes to gnawing, squirrels in a decking sub-base cause damage that is both rapid and difficult to remediate. Prevention, correctly specified, is the only reliable answer.
Why squirrels use decking sub-bases
The grey squirrel (Sciurus carolinensis) is an adaptable, highly intelligent animal that exploits any available structural cavity for nesting and food storage. Raised decking provides both. The void beneath a deck frame is dry, sheltered, thermally stable, and, in most gardens, entirely undisturbed. It closely replicates the tree cavity environments that squirrels naturally exploit.
Squirrels are most active in spring and autumn — when breeding nests are being established and when food caching for winter begins. During these periods, a garden with squirrel activity will see animals investigating decking perimeters consistently. Any accessible gap in the perimeter will be used, widened if necessary, and established as a nest site within days.
Unlike rats or mice, squirrels typically access sub-base voids from above — jumping onto deck boards and squeezing through gaps in the deck surface — or from the perimeter at ground level. Both routes need to be addressed for comprehensive exclusion.
The damage squirrels cause beneath decking
Squirrels are powerful gnawers. Their incisors are harder and their jaw force considerably greater than that of rats or mice. Beneath decking, squirrels gnaw structural timber — joist edges, bearer faces, deck board undersides — both to maintain their teeth and to modify the space. The structural consequences of sustained squirrel gnawing on floor joists are more severe than equivalent rodent damage.
Squirrels also cache food in sub-base spaces. Buried nuts, seeds, and other food items attract other pest species and, when they decompose, create conditions favourable to fungal growth in the sub-base. In conjunction with the nesting material they bring in, squirrels rapidly fill a sub-base void with organic material that retains moisture and accelerates timber decay.
Removal of an established squirrel nest requires handling contaminated organic material. Squirrel nesting material in a decking sub-base is an unpleasant and labour-intensive problem to address. In many cases, section of the deck must be removed to allow full clean-out.
Why squirrel control fails without structural exclusion
Squirrels are a protected species in terms of certain control methods, and non-lethal deterrents are largely ineffective against an animal that is highly motivated to access a specific nesting site. Live trapping can remove individual animals but does not prevent re-colonisation from the local population.
Physical exclusion is the only approach that permanently resolves the problem. For existing decking, sealing the perimeter and deck surface gaps with appropriate mesh is the primary strategy. For new construction, a sub-base barrier at ground level eliminates the most accessible entry route before the deck is built.
Sub-base barrier specification for squirrel exclusion
Squirrels are significantly larger than mice and rats, which simplifies the mesh specification in one respect: they cannot pass through a 20–25mm opening. However, the barrier still needs to be installed correctly — with a welded construction that resists gnawing, and a perimeter detail that does not leave gaps at the deck edge.
A welded wire mesh with a 7.66mm opening, as used in BaseShield™ SubBase Defence, is more than adequate for squirrel exclusion and simultaneously excludes mice and rats. Using a purpose-built barrier product also ensures the mesh is hot-dip galvanised for long-term ground contact performance.
The right product for this application
BaseShield™ SubBase Defence excludes squirrels, rats, and mice with a single barrier installation. The welded construction resists gnawing and the roll format covers the full deck footprint efficiently before the frame is fixed.
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
For new decking construction, deploy BaseShield before fixing the frame. For existing decking with squirrel access, a perimeter barrier dug in to 200mm depth and folded flat beneath the perimeter joist provides useful secondary protection, though full footprint coverage via retrofit is not achievable without lifting the structure.
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.