Large parts of Tonbridge town centre and the Medway valley sit in Environment Agency flood zones 2 and 3, and any landscaping that changes levels, raises edging or covers permeable ground is scrutinised against flood risk. On Weald Clay plots in those zones we typically set patio thresholds above the property DPC, pipe surface water away from the house to a soakaway or storm drain rather than infiltrating into the clay, and specify SuDS-friendly permeable surfaces for paths. EA informal advice is worth obtaining before finalising a spec on any flood-zone frontage, and Tonbridge & Malling BC's LDC route gives written confirmation of the planning position.

Tonbridge & Malling Borough Council follows the standard Class E Permitted Development framework — a ground-level patio is generally exempt, raised decking or terracing over 300mm is not, and outbuildings within the standard limits are usually permitted. The Tonbridge-specific nuance is that valley-floor streets in flood zones 2 and 3 are subject to EA guidance treating any ground-level change — including new raised edging or a patio built above existing DPC — as potentially affecting flood storage. TMBC strongly recommends applying for a Lawful Development Certificate on these streets before works start; the LDC gives written confirmation the scheme is PD, which also removes ambiguity with insurers.

Tonbridge splits between Weald Clay through the town-centre flats and river valley, and Tunbridge Wells Sand and Ashdown Sandstone on rising ground towards Tunbridge Wells and Hildenborough. Weald Clay shrinks and swells seasonally, drains poorly, and causes the lifted or cracked slabs common on older Tonbridge patios — on clay plots we specify a deeper MOT Type 1 sub-base, geotextile membrane and flexible jointing throughout. Sandstone plots on the ridge drain well and suit a lighter, permeable build-up. On flood-zone frontages we set patio thresholds above the property DPC and pipe surface water away rather than relying on infiltration into the clay.