Artificial Grass Installation: Sub-Base, Membrane, Jointing & Drainage

Quick Answer: A professional artificial grass installation requires a compacted sub-base of minimum 50mm (residential) to 100mm (commercial/heavy use) of MOT Type 1 or sharp sand, a weed suppressant membrane, and a correctly tensioned and fixed grass layer with invisible joins. Drainage is typically through the grass backing and sub-base to the soil below; on clay soils or concrete, a drainage channel or aggregate drainage layer is required. There are no Building Regulations requirements for artificial grass in gardens, but planning permission may be needed in Conservation Areas.

Summary

Artificial grass has grown rapidly in popularity in UK gardens over the past decade, driven by low maintenance and year-round usability. The quality of finished installations varies enormously — from carpet laid on bare soil (which fails within a year) to properly engineered installations on compacted sub-bases that last 15–20 years. The difference in cost between a poor and a proper installation is modest; the difference in outcome is very significant.

The key elements of a lasting installation are: adequate sub-base depth and compaction (the most commonly skimped step), effective weed suppression beneath the membrane, correct grass tensioning and fixing at edges and joins, and drainage appropriate to the soil type. On clay soils or over concrete (e.g., converting a patio), the drainage must be specifically designed because water cannot pass through to the native soil.

From a regulatory perspective, artificial grass is largely unregulated. Planning permission is not generally needed, though Conservation Areas and Listed Building curtilages may have restrictions. The main considerations are the environmental arguments (heat island effect, loss of biodiversity, microplastics from infill) which are increasingly relevant to client conversations, and the planning pressure in some LPAs to limit artificial grass in front gardens.

Key Facts

• Sub-base depth (domestic) — minimum 50mm compacted sharp sand over cleared ground; 100mm MOT Type 1 for heavy use or poorly draining soils
• Sub-base depth (sports/commercial) — 150mm+ engineered sub-base; designed to SAPCA guidelines
• Pile height — 20–25mm: flat/occasional use; 30–37mm: general garden; 40–50mm: luxury appearance; taller piles flatten faster under foot traffic
• Dtex (density) — a measure of grass weight per 10,000m of fibre; higher dtex = denser, more durable; quality residential grass typically 11,000–15,000 dtex
• Backing — most artificial grass has a latex or polyurethane (PU) backing; PU backing tends to be more durable and dimensionally stable; backing must be permeable (holes or open weave) for drainage
• Weed membrane — woven polypropylene membrane under the grass prevents weed growth through the grass; semi-permeable allows drainage; do not use solid polythene as it traps water
• Fixing at edges — nails (bright round head, 38mm or 50mm) at 100–150mm centres; staples on decking; proprietary aluminium nail strip on concrete
• Jointing — seam tape (self-adhesive or glued) under joins; brush pile direction both sides of join before adhering; joins should be at right angles to direction of view
• Infill — kiln-dried silica sand brushed into pile at 3–5 kg/m² keeps blades upright; optional crumb rubber infill adds cushioning (but raises microplastic concerns)
• Drainage on concrete — surface water cannot drain through concrete; lay aggregate drainage layer (40mm 6mm pea gravel) over concrete + permeable membrane + grass; drain aggregate to edge channel
• Drainage on clay — install perforated drain pipe under sub-base to collect water that pools above clay horizon; connect to soakaway if possible (test first)
• Planning in Conservation Areas — may require consent if it materially changes the character of the area; check with LPA
• Heat — artificial grass can reach 50–70°C surface temperature in summer sun; important to advise clients, especially those with children and pets
• Guarantee — manufacturer warranty typically 8 years for residential; installation guarantee separate from product guarantee

Quick Reference Table

Detailed Guidance

Ground Preparation

Step 1: Remove existing grass and topsoil Scalp the existing lawn to 75–100mm below the intended finished surface level. Remove all roots, debris, and organic matter. Never lay artificial grass over existing topsoil — it will compact unevenly, organic matter will decompose and create settlement, and weeds will push through.

Step 2: Treat with weedkiller (optional but recommended) Apply a non-residual glyphosate-based weedkiller (e.g., Roundup Fast Action) to the exposed soil. Leave 7 days before proceeding. This targets persistent weeds that will push through membrane over time.

Step 3: Install edging Before laying the sub-base, fix timber or composite edging boards at the perimeter of the grass area. 100mm × 38mm treated softwood fixed with 75mm galvanised nails to timber pegs is standard. This creates a neat boundary for the sub-base and gives a firm edge for nailing the grass.

Step 4: Sub-base Lay and compact the sub-base (see table above for specification by substrate type). Compact in lifts with a vibrating plate compactor. Final surface: firm, level, and with the same fall profile as intended for the finished grass (1:80 minimum away from buildings).

Step 5: Weed membrane Lay woven geotextile weed control membrane over the entire sub-base, lapping joints by 200mm. Staple to the sub-base at 500mm centres. The membrane prevents weed growth without blocking drainage.

Laying the Grass

Unroll the grass and allow it to acclimatise for 1–2 hours in warm weather — this reduces the rubber smell and allows any dimensional changes from temperature to stabilise before cutting and fixing.

Pile direction: artificial grass has a pile direction (the blades lean in one direction). Always lay the pile leaning toward the main viewing direction (toward the house, or toward the garden from the seating area). Consistent pile direction across joined sections is critical for invisible seams.

Cutting: use a sharp Stanley knife or carpet knife. Cut from the back to avoid cutting visible fibres. Make straight cuts along the backing ribs.

Jointing: for joins, apply seam tape (minimum 300mm wide) sticky side up under the join. Butt the grass edges (do not overlap) and adhere firmly. Run a heavy roller or tamp with a flat board. The join is visible until infill is brushed in.

Edge fixing: fold the grass over the timber edging board and fix with 38–50mm bright round head nails at 100–150mm centres. Trim surplus. The timber edging board provides a firm fixing base and a clean edge to the installation.

Drainage for Concrete Substrates

This is the most technically demanding situation. The existing concrete must slope to an outfall or a channel drain must be installed. Without drainage, water will pool on the surface (backing is permeable but if the drainage layer beneath is saturated, it cannot accept more water).

Solution A: Drainage layer over concrete

• Lay 40mm pea gravel (6–10mm rounded) over the concrete
• Install 150mm-wide linear channel drain at the lowest point or at perimeter
• Connect channel to soakaway or surface water outlet
• Lay weed membrane over gravel
• Lay artificial grass over membrane

Solution B: Raise the perimeter

• At the low edge of the concrete, install an ACO or polymer channel drain with fall to outlet
• Lay grass directly on permeable geotextile over concrete
• Not suitable if concrete is not draining quickly enough — drainage layer is preferable

Infill Application

Silica sand infill (kiln-dried, fine grain) should be applied after laying and fixing, then regularly topped up:

• Application rate: 3–5 kg/m² (spread with a drop spreader or by hand and brush in)
• Use a stiff broom or power brush to work infill into the pile
• Repeat twice — first pass at half rate, second pass at full rate
• Re-apply after heavy rainfall washes infill to the edges
• Top up annually as part of maintenance

For sports pitches and commercial applications, crumb rubber (SBR) infill is used at higher rates (5–10 kg/m²) for cushioning. Increasing awareness of microplastic contamination from crumb rubber has led some installers to offer cork, silica, or EPDM alternatives.

Maintenance Guidance (Pass on to Client)

• Brushing: brush against the pile direction monthly with a stiff broom or power brush to keep blades upright
• Cleaning: rinse with a garden hose for pet waste; diluted mild soap solution for stains; avoid petroleum-based solvents
• Leaves and debris: blow or rake off regularly; leaves break down and create organic matter on the surface
• Pets: rinse immediately after dogs urinate; apply artificial grass enzyme cleaner (e.g., Simple Solution, Zero Odour) monthly in pet areas
• Weeds: despite the membrane, some weeds may grow in the infill layer over time; treat with a non-bleach-based spot weedkiller

Frequently Asked Questions

How long will artificial grass last?

Quality residential artificial grass with proper installation typically lasts 12–18 years. Shorter-pile (under 25mm) or sports-quality grass with higher dtex lasts longer. The main degradation is UV fading (most modern grass is UV-stabilised for 8+ years) and mechanical wear in high-traffic areas. The latex backing degrades before the blades — better-quality PU-backed grass lasts longer.

Can I lay artificial grass on top of an existing lawn?

You can but should not. Laying directly over an existing lawn leaves organic matter under the grass that will decompose, causing uneven subsidence, odour problems, and creating ideal conditions for weeds to grow through the membrane. Always remove topsoil and organic material first.

Is artificial grass bad for the environment?

It eliminates the biodiversity value of a real lawn (pollinators, birds, invertebrates), increases surface water run-off on clay soils (less infiltration than grass), generates heat in summer (significantly warmer than natural grass), and contains synthetic materials that will ultimately go to landfill. For clients concerned about this, mention alternatives: hard-wearing drought-tolerant turf varieties (fescues, crested dog's-tail), gravel gardens, or permeable paving with planted beds.

Do I need planning permission to install artificial grass?

Generally no for rear gardens. For front gardens, some LPAs have issued guidance discouraging or restricting artificial grass in Conservation Areas, as it can materially affect the character of the area. Some planning conditions on new developments specifically prohibit artificial grass in front gardens. Check with the LPA if the property is in a Conservation Area or if the client received any planning conditions when they bought or built.

Regulations & Standards

• SAPCA (Sports and Play Construction Association) — guidance on sub-base and drainage specifications for artificial sports surfaces

• BS 7188 — impact-absorbing playground surfaces (applies to domestic artificial grass only if used in play area context)

• Town and Country Planning (GPDO) 2015 — Schedule 2, Part 1, Class F — hard surfacing in front gardens (implications for artificial grass over 5m²)

• Water Industry Act 1991 — surface water disposal obligations for large artificial grass areas

• SAPCA — Artificial Grass Technical Guidance — installation standards for sports surfaces

• Fieldsports Channel — Artificial Grass Guide

• Which? — Artificial Grass Guide — consumer guidance

• Planning Portal — Front Garden Paving — planning rules for hard landscaping

• patio laying — sub-base and drainage principles for hard landscaping

• drainage landscaping — drainage solutions for clay soils

• block paving — permeable paving alternatives to artificial grass