Landscaping and External Works After an Extension

• **1. Garden reinstatement**:
• During construction of a rear extension, the garden directly behind the house is typically devastated — used for material storage, scaffolding bases, skip placement, concrete mixing, and subcontractor access. The standard of reinstatement to be included in the building contract should be specified before work starts:
• •Topsoil removal and storage, returned and re-levelled at completion (better quality than buying new topsoil)
• •Lawn reinstatement: turfing or seeding — specify which in the contract
• •Boundary fencing or walls: whether temporary hoarding during construction is removed and replaced with permanent fencing at completion
• •Tree and shrub protection during construction and replacement of any damaged planting

• **2. Paving and hard landscaping**:
• The patio area immediately behind a kitchen/dining extension is typically redesigned as part of the project — the existing patio may be covered by the extension, the level may change, or a new terrace is created to link the extension to the garden. Key considerations:
• •Levels: the new extension floor level determines the level at which the external paving must meet the threshold. French doors, bifold doors, or sliders must meet the external paving at a level that allows a weathertight threshold (typically 150mm above the external paving, or 'level threshold' with a drainage channel)
• •Materials: Indian sandstone (£60–£120/m² supply and lay), porcelain (£80–£150/m²), natural limestone (£90–£160/m²), and concrete flags (£40–£70/m²) are the common choices
• •Sub-base: all paving requires a proper MOT Type 1 sub-base (100–150mm compacted), sharp sand bed, and appropriate jointing — paving laid on bare soil or insufficient sub-base will move, crack, and weeds will colonise the joints within 2–3 years
• •Drainage: paved areas adjacent to the building must slope away from the extension at minimum 1:80 (12.5mm fall per metre) to prevent water standing against the wall and causing damp issues

**3. Drainage gullies and channel drains**: At the threshold of bifold or sliding door openings, a channel drain (linear drain) is typically installed to catch water before it reaches the threshold. Without it, rain-driven water can enter under the door seal during heavy rain. Linear drainage channels: £150–£300/m supply and install, coordinated with the external paving level.

• **4. Steps**:
• Where there is a level change between the extension threshold and the garden, steps must be designed and built. Steps in a private garden have no minimum requirement for rise and going (unlike internal stairs), but for comfortable and safe use:
• •Going (tread): minimum 280mm, preferred 350mm+
• •Rise: 100–175mm; lower rises (120–150mm) are more comfortable for garden steps
• •Nosing: bullnose or chamfer to the front edge of each tread
• •Number of steps: typically 1–3 steps for the modest level changes at a ground-floor extension, with 1–3 steps of 150mm rise each being most common in London gardens
• •Cost: approximately £400–£900 per step (cast-in-situ concrete cheek walls + natural stone tread)

• **5. Garden walls and boundary structures**:
• The party boundary wall between the property and the neighbour is often disturbed during the extension construction — the extension is built up to or close to the boundary. Where the boundary wall is shared (a party wall), any damage must be made good. Where a new boundary structure is needed, this should be specified:
• •Brick boundary wall (1.8m high): approximately £300–£500/m supply and build (materials and labour)
• •Timber fence panel with capped posts: £80–£200/m
• •Feather-board fence with gravel board: £100–£180/m
• •Note: a boundary wall over 2m height adjacent to a highway (front garden/public road) requires planning permission under the Permitted Development rules

**External lighting**: Outdoor lighting transforms an extension's connection to the garden — making the space usable after dark and creating a visual reference from inside. Lighting should be co-ordinated in first fix:

• *Types of outdoor lighting*:
• •Security lighting (PIR-activated floodlights): typically 2–4 fittings covering the rear and side access, connected to a dedicated exterior circuit
• •Atmospheric lighting (downlights in soffit of extension, wall-mounted luminaires, spike lights in the garden, uplighting to trees): planned as part of the extension design, cable routes installed in first fix before rendering and paving are laid
• •Step and path lighting: low-level step lights or linear LED strips under step overhangs; cable to be laid before steps and paving are finished

*Installation note*: exterior lighting must be IP44 rated (splash-proof) or higher for outdoor use. IP65 or higher for directly exposed external locations. Part P notifiable work — use a Part P registered electrician.

**External power sockets**: Weatherproof double sockets in the garden are useful for electric mowers, power tools, and external appliances. Typically installed on the outside wall of the extension, connected from the extension's ring main. RCD protection is mandatory for all outdoor sockets (BS 7671 requirement). Cost: £150–£400 per socket installation including weatherproof cover plate and RCD protection.

**Water supply for the garden**: An external garden tap on the rear wall of the extension is one of the most useful and underspecified provisions in an extension — the tap is connected from the cold water supply in the extension and includes an inside service valve for winterising. Install the supply pipe in first fix before the external render and paving are complete. Cost: £200–£500 for a single garden tap including pipework, inside service valve, and tap.

**Irrigation**: For larger gardens or gardens with planting beds, a drip irrigation system can be connected from the garden tap. Micro-irrigation systems for a medium London garden (50–100m² planted area): £800–£2,500 supply and install including automatic timer.

Most garden landscaping and paving is permitted development — but there are important exceptions:

**1. Paving in the front garden**: Under changes to the GPDO in 2008, paving more than 5m² of a front garden (between the house and the public road) with an impermeable material (concrete, tarmac, standard porcelain or sandstone without permeable jointing) requires planning permission. This is to address surface water run-off concerns.

• Exceptions:
• •Permeable paving (gravel, permeable block paving with open jointing, permeable concrete paving) does not trigger this rule — any area can be paved without permission
• •Any size of impermeable paving in the rear garden is permitted development

• **2. Boundary walls**:
• •A wall over 1m high adjacent to a highway: requires planning permission
• •A wall over 2m high not adjacent to a highway: requires planning permission
• •In a Conservation Area: any new boundary wall that was not previously there requires planning permission

**3. Outbuildings and garden structures**: See the separate guide on garden rooms and outbuildings for the full permitted development rules.

• **4. Surface water drainage**:
• Building Regulations Part H3 requires that surface water run-off from new hardstanding adjacent to the extension is managed without increasing the burden on the public sewerage system. Options:
• •Drainage to soakaway (preferred)
• •Drainage to a watercourse if available
• •Drainage to the combined or surface water sewer (requires the water authority's approval and may not be permitted)

For a large new paved area (over ~50m²), a soakaway assessment may be required.

• **London 2025 costs — typical external works package for a 4m × 6m kitchen extension**:
• •Garden reinstatement (top soil, turfing 30m²): £1,500–£3,000
• •Rear patio (15m² sandstone, sub-base, jointing): £2,500–£5,000
• •Linear channel drain at bifold threshold (3m): £500–£900
• •Steps (2 steps, natural stone treads): £800–£1,600
• •Garden tap: £300–£500
• •External lighting (4 downlights in soffit + 2 wall lights): £800–£1,800 supply and install
• •Total typical external works budget: £6,000–£13,000

This is a meaningful budget item that should be included in the project estimate from the start — not added as a last-minute extra.