External Public Paving Slip Testing

Where external paving testing is commissioned

• Public footpaths and pedestrianised zones (local authorities)
• Town square and high-street paving (BID partnerships and councils)
• Approach paving to commercial and public buildings
• Retail park and shopping centre external common parts
• School playgrounds and external circulation routes
• Hospital and care home approach paving
• Transport interchange paving (bus stations, tram stops)
• Hospitality external smoking and dining areas

The seasonality problem

External paving PTV is not a single annual number. The same surface can produce:

• PTV 45 in summer, dry, swept — nominally compliant
• PTV 28 in autumn after leaf-litter deposition — moderate slip risk
• PTV 18 with algae bloom in damp shaded sections — high slip risk
• PTV 12 with surface frost — high slip risk
• PTV 35 with de-icer residue once frost has passed

Single-visit data therefore captures one snapshot. Quarterly or seasonal testing programmes capture the variation.

Algae — an underappreciated factor

Biological algae growth on damp shaded paving is the single most consistent finding across our local-authority external testing. Algae typically reduces PTV by 10–20 points wet. Treatment regimes that biocide-clean external paving annually maintain materially better PTV than estates with no algae management programme.

Leaf litter and seasonal contamination

Wet leaf litter, particularly oak and plane, deposits a thin pectin-and-water film on paving as it decomposes that affects PTV beyond the obvious mechanical interference. Sweeping the leaves does not necessarily remove the residual film. Pendulum testing in autumn captures this; mid-summer testing does not.

Local authority compliance

Highway authorities have section 41/58 Highways Act duties relating to maintenance of the highway in a safe condition. Footpath slip claims under the Highways Act require evidence of the maintenance regime. Pendulum data is not a complete defence on its own — the Highways Act case law is more nuanced — but it is a substantive contributor to demonstrating reasonable practicable steps.

Town centre regeneration projects

Public-realm regeneration projects (high-street improvements, town-square refurbishments) typically include slip-resistance specifications drawn from BS 8204-1 or specific public-realm guidance. Pendulum testing at handover closes out the specification; periodic testing thereafter monitors the surface's ageing.