External Works and Patio Design for London Homes

Most straightforward hard landscaping in a private residential garden does not require planning permission. However, there are important exceptions:

**Paving the front garden:** Since 2008, planning permission is required to pave a front garden with an impermeable surface (concrete, tarmac, standard porcelain) if the area is more than 5m². Using permeable paving (gravel, permeable block paving, permeable resin-bound surfaces) does not require permission — and is strongly encouraged to manage surface water run-off and reduce sewer flooding risk in London.

**Raised decking:** Decking in a residential garden is permitted development if it is no higher than 300mm above the ground. Decking above 300mm (elevated decking structures or roof decks) requires planning permission.

**Garden rooms and outbuildings:** Garden outbuildings (garden rooms, home offices, studios, storage) are subject to permitted development rules: maximum 2.5m height if within 2m of the boundary; up to 4m (dual-pitch roof) or 3m (other) if more than 2m from the boundary; maximum 50% of the original garden area; not to the front or side of the property (some restrictions). In Conservation Areas, outbuildings require planning permission.

**Retaining walls:** Retaining walls do not typically require planning permission. However, a retaining wall over approximately 1m high requires structural design — particularly in London where the combination of clay soils, groundwater, and tree root pressure makes wall stability a genuine structural concern. A structural engineer should design any significant retaining wall.

**Trees:** In Conservation Areas, works to trees (pruning, removal) require notification to the council (and sometimes consent). Any significant tree in London may be protected by a Tree Preservation Order (TPO). Check before undertaking any tree works.

• **Porcelain paving:**
• The most popular external paving for contemporary London gardens. Available in large format tiles (600×900mm, 900×900mm) and a wide range of finishes. Key considerations:
• •For external use, porcelain must be the correct specification (anti-slip rating R11 or better for areas that can be wet — patios, terraces)
• •Requires a full mortar bed on a properly prepared sub-base (MOT Type 1 or concrete) — not suitable for loose laying
• •Frost-resistant specification required
• •Cost for supply and lay (mid-range porcelain, prepared sub-base): £80–£150/m²

**Natural stone:** Indian sandstone, limestone, granite, and slate are all used in London gardens. Limestone and sandstone require sealing and maintenance. Granite is extremely durable and low-maintenance. Supply and lay: £90–£200/m² depending on stone type.

**Brick paving:** Traditional London stock brick or clay pavers complement Victorian and Edwardian properties. Often the most contextually appropriate choice for period properties. Requires a sand bed on a compacted sub-base. Cost: £70–£130/m².

**Resin-bound gravel:** Permeable (important for front gardens), attractive, and low-maintenance. UV-stable resin binders available in a range of aggregate options. Requires a rigid base (tarmac or concrete). Cost: £70–£120/m² installed.

• **Timber decking:**
• Hardwood (Ipe, Cumaru, Bangkirai) or composite decking (Trex, Millboard, Cladco) are both popular for London gardens. Hardwood is natural and ages gracefully; composite requires virtually zero maintenance. Cost:
• •Hardwood decking: £120–£200/m² supply and install
• •Composite decking: £150–£250/m² supply and install

• **Surface water drainage — London's critical consideration:**
• London's combined sewer system (which handles both sewage and surface water in much of inner London) is operating at or beyond capacity. Flooding from impermeable surfaces — driveways, patios, and extensions — is a growing problem. For this reason:
• •New hard landscaping should use permeable materials where possible or include surface water drainage to a soakaway or rain garden
• •Thames Water and the borough councils encourage permeable paving and Sustainable Drainage Systems (SuDS)
• •For larger external works, a drainage design may be required as part of planning approval

• **Subbase preparation:**
• All hard landscaping requires adequate subbase preparation:
• •Minimum 100mm compacted MOT Type 1 (crushed stone) sub-base under paving and decking in areas subject to foot traffic
• •For areas subject to vehicular loading (driveways): minimum 150mm MOT Type 1 + concrete slab or tarmac
• •Where London clay is present, additional consideration is required — clay shrinks and swells seasonally, affecting paving stability. A deeper sub-base and/or compacted hardcore is typically required.

• **Retaining walls and level changes:**
• Many London gardens have level changes — either natural slope or changes created by the extension footprint. Retaining a level change requires:
• •A suitable retaining structure (brick wall, blockwork wall, timber sleepers, gabion baskets)
• •Adequate drainage behind the wall (a 'French drain' or granular fill with drainage channel) to prevent water build-up and wall failure
• •For walls above approximately 800mm height: structural design recommended

• **Typical external works costs in London:**
• •Small patio (20–30m²) + preparation + drainage: £5,000–£10,000
• •Medium patio with steps and feature planting beds (40–60m²): £10,000–£20,000
• •Composite decking structure (20m²): £6,000–£12,000
• •Garden room/home office outbuilding (15–25m², timber frame, insulated): £15,000–£35,000