What Goes Under Artificial Grass? A Complete Guide

If you’ve got as far as picking out a synthetic lawn, there’s a good chance you’ve also started wondering what actually sits underneath it. It’s a fair question, and an important one. The turf itself gets all the attention, but the sub-base underneath is what determines whether your new lawn lasts 20 years or starts looking tired and lumpy within a couple of summers.

This guide walks through what actually goes under artificial grass, why it matters so much in New Zealand conditions, and what to look for when you’re choosing an installer or comparing quotes.

Why the Sub-Base Matters More Than the Turf

It’s tempting to think of synthetic turf as a simple “roll it out and you’re done” product. In reality, the turf is only as good as what’s beneath it. A premium product laid over a poorly prepared base will still develop dips, drainage problems and uneven wear. A modest product laid over a properly built base will outperform it every time.

This is especially true here in New Zealand, where many sections deal with heavy clay soils, particularly around Auckland, that hold water and shift slightly with moisture changes through the seasons. Skipping proper base preparation on clay-heavy ground is one of the most common reasons synthetic lawns fail early.

The Layers Under a Quality Artificial Lawn

A correctly built sub-base typically includes a few key layers, each doing a specific job:

1. Excavation and Sub-Grade Preparation

The existing soil, grass, roots and any debris are removed to a suitable depth, usually around 75 to 100mm for residential lawns, more for areas with poor drainage or heavy clay. The exposed sub-grade is then compacted to create a stable starting point.

2. Base Aggregate Layer

A compacted aggregate layer, often a GAP40-style crushed rock, forms the structural foundation. This layer does the heavy lifting for drainage, allowing water to move down and away rather than pooling under the turf. On sites with particularly poor natural drainage, this layer may need to be deeper or supplemented with additional drainage solutions.

3. Weed Membrane

A weed barrier sits between the base layers and the turf to stop weeds pushing up through the lawn from below. It’s a small step that saves a lot of frustration later, particularly on sections backing onto reserves or with persistent weed issues.

4. Finer Levelling Layer

A finer compacted material, sometimes referred to as crusher dust or a similar fine aggregate, sits on top of the base layer. This is what gets carefully screeded and levelled to create the smooth, even surface the turf is laid onto. This step is where a lot of the “look” of the finished lawn actually comes from. Any unevenness here shows up as bumps and dips later.

5. Shock Pad or Drainage Pad (Where Needed)

For play areas, pet zones or anywhere extra cushioning or drainage is wanted, a shock and drainage pad can be installed under the turf itself. This adds underfoot comfort and helps water disperse both vertically and horizontally, which is particularly useful on sites with limited fall or slope.

Choosing Materials for Longevity

Not every base build needs every layer at full depth. The right specification depends on:

• Soil type: Clay-heavy sites generally need a deeper, more robust aggregate base than free-draining sandy soils
• Drainage and fall: Flat sections or those prone to surface water need extra attention to base depth and any additional drainage measures
• Intended use: A lawn for general use needs a different base than a high-traffic kids’ play area or a pet zone that needs to manage urine and odour
• Climate exposure: Areas exposed to heavy rainfall need a base built to move water away quickly, not just hold the turf in place

This is where getting advice from a manufacturer who actually understands New Zealand soil and rainfall patterns pays off. Imported product ranges and generic installation guides aren’t always built around our conditions. As New Zealand’s only local synthetic turf manufacturer, TigerTurf designs and builds base specifications around how our soil, rainfall and seasons actually behave, not a generic international standard.

Common Mistakes to Avoid

A few issues come up again and again with poorly performing synthetic lawns:

• Base too shallow: Cutting corners on excavation depth to save time or cost
• Skipping compaction: Aggregate that isn’t properly compacted will settle unevenly over time
• No weed membrane: Leads to weed growth pushing through the turf within a year or two
• Ignoring drainage: Particularly on clay soils, where water needs somewhere to go

Getting It Right From the Start

The sub-base isn’t the exciting part of a synthetic turf project, but it’s the part that determines whether you’re happy with your lawn in five years’ time, not just on installation day. If you’re comparing quotes, it’s worth asking exactly what base specification is included, not just what turf product is being quoted.

For a clearer picture of how the full installation process comes together, including base preparation, take a look at our synthetic turf installation process and get in touch with our team for advice specific to your section.

Getting the ground right is the unglamorous, genuinely important first step. Get that sorted, and the lawn on top has every chance of looking great for decades.