Hedgehog gaps and connectivity conditions

A hedgehog gap is a 13cm by 13cm opening at ground level in a boundary fence or wall, and it appears in planning conditions on housing schemes because habitat connectivity is now a routine expectation rather than an optional extra. The dimension is the one used in the guidance authorities borrow from, and it exists because a hedgehog will pass through that aperture and a domestic cat will think twice. The measure costs almost nothing at construction stage and fails constantly at handover, when a management company replaces a fence panel or a resident blocks the hole with a paving slab.

So the useful question is not whether to provide gaps. It is how to word the condition and the estate documents so the gaps are still open in five years.

Why connectivity is conditioned on housing schemes

Three strands of policy converge on it.

Public authorities carry a duty to have regard to conserving biodiversity in exercising their functions, and that duty was strengthened to a duty to conserve and enhance by the Environment Act 2021. Hedgehogs are a species of principal importance for conserving biodiversity in England, which brings them squarely within that duty. And most adopted local plans now carry a policy on habitat connectivity, green infrastructure or wildlife corridors that an officer can cite.

The evidence side is straightforward. Suburban gardens are a significant part of the remaining habitat, and a housing estate enclosed by continuous close boarded fencing on concrete gravel boards divides that habitat into parcels too small to support foraging. Individual animals need to move across several gardens a night.

A Preliminary Ecological Appraisal will normally recommend connectivity measures where the site is within or adjoining a suburban or rural matrix, and the condition follows from that recommendation rather than appearing from nowhere.

Gap dimensions and position in boundary treatments

Specify the gap in the boundary treatment detail, not in a covering note.

The opening should be at ground level, 13cm by 13cm, positioned where the ground on both sides is level enough to use and away from the point where a bin or a shed will end up. One gap per boundary is the usual expectation, which on a typical plot means two or three.

Construction detail matters more than the dimension. A close boarded fence on a concrete gravel board has to have the board notched or a purpose made gravel board with an aperture used, because cutting the fence panel above the board achieves nothing. A brick or block wall needs the opening built in, with the lintel or arch detailed, since retrofitting means breaking out masonry. Post and rail fencing, hedges and native hedgerow with an occasional rail are permeable by default and remove the problem altogether.

Where the boundary is a retaining structure or a party wall, gaps are not appropriate and the condition should say where the connectivity route runs instead.

Management company rules that undo the provision

This is where the measure is most often lost, and planning conditions alone will not prevent it.

The sequence is predictable. A fence panel is damaged, the management company replaces it with a standard panel and a standard gravel board, and the gap is gone. Or the estate rules require uniform boundary treatment and a resident replacing a fence installs one without an aperture. Or a new owner blocks the hole because a dog escaped through it.

Two documents fix this, and neither is a planning condition. The estate management plan or the transfer covenants should record that boundary apertures are a planning requirement and must be maintained and reinstated on replacement. And the homeowner information pack should explain what the gap is for, because residents who understand it keep it.

Ask for both to be secured, either through the condition wording or through the section 106 agreement where one exists. A condition that requires the developer to install gaps and says nothing about the management regime discharges on the day of the final inspection and has no purchase afterwards.

Gully gratings, trenches and construction risk

During construction the site is more dangerous to hedgehogs than the finished estate.

Open foundation trenches and service trenches are the main hazard, because an animal that falls in cannot climb out. The standard measures are to backfill or cover trenches at the end of each working day, to place a means of escape such as a scaffold board ramp in any trench left open, and to check trenches before backfilling or pouring. Add the checks to the toolbox talk rather than only to the method statement.

Gully pots and drainage chambers left uncovered do the same thing. So do stacked materials that create a void, pallets left on soft ground, and bonfires built and left overnight before burning.

None of this is expensive. It needs a named person responsible and a line in the daily site check, and it belongs in the construction environmental management arrangements alongside the tree protection measures.

Landscape design that supports movement

Gaps in fences are the minimum. The landscape scheme is what makes the estate usable.

What helps: native hedgerow instead of fencing on rear and side boundaries wherever the layout allows, continuous planted verges rather than isolated beds, log piles and leaf litter retained in corners, dense low planting along routes, gaps beneath gates rather than flush thresholds, and avoiding continuous kerb upstands along routes an animal would take. Lighting matters too, because a brightly lit corridor is avoided, and the dark route principles applied for bats serve hedgehogs as well.

What hurts: continuous hard boundary treatment, sheer sided ornamental water features, close mown amenity grass with no structure, and steel edging set proud of the surface.

Put the connectivity route on a plan within the Landscape Strategy so the officer can see it as a network rather than a list of holes. A drawn route also survives design changes better than a written commitment.

Drafting the condition so it survives handover

1. Require the gaps to be shown on the approved boundary treatment drawing, with the dimension and the ground level position detailed.
2. Require the gravel board or wall detail to accommodate the aperture, rather than the panel above it.
3. State the number of gaps per plot boundary rather than a site total.
4. Require a connectivity plan showing the intended route across the site.
5. Require the estate management plan or transfer documents to include a maintenance and reinstatement obligation.
6. Require a homeowner information note explaining the purpose.
7. Require photographic evidence of installation before occupation of the final plot.

Recording compliance

Photograph every gap as it is installed, with the plot number and a scale in the frame, and keep the record in the same file as the tree protection photographs. Discharge submissions that arrive with a spreadsheet and no images tend to come back.

Where a later design change removes a boundary, submit the revised connectivity plan rather than hoping the change goes unnoticed. Officers compare the as built boundary treatment against the approved drawing on the final inspection more often than developers expect.

Where the measure is largely symbolic

An honest assessment matters here, because overselling connectivity damages the credibility of the rest of an ecological submission.

On a site enclosed by dual carriageways, or a single infill plot in a dense terrace with walled gardens on every side, gaps in the new fence connect one garden to another garden and nothing more. The measure is still worth providing, because a network is built from individual permeable boundaries and the cost is negligible. But it should be described as what it is rather than presented as mitigation for habitat loss.

It is also not a biodiversity unit. Connectivity measures do not score in the statutory biodiversity metric, so they cannot substitute for the gain a scheme has to deliver. The metric must be completed by a competent person under the Environment Act 2021 regime, and a Biodiversity Net Gain Assessment is a separate exercise from the connectivity condition. Where the ecological report treats gaps as a gain, an officer will notice.

An illustrative example: a 24 plot scheme on the edge of a village, with rear gardens backing onto arable land. Boundary treatment is native hedgerow to the rear with post and rail, and close boarded fencing between plots with a notched gravel board and one aperture per boundary. A connectivity plan shows a continuous route from the rear hedgerow through the plots to a retained hedge on the street frontage. The management plan carries a reinstatement obligation, and the sales pack includes a short note. The condition discharges on 48 photographs and one drawing. The wider significance of effects is set out properly in the ecological impact assessment, which is where the real mitigation case sits.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.