Re-levelling a sunken lawn is a satisfying DIY project that most NZ homeowners can tackle themselves, provided the cause of the sinking is straightforward. Before you reach for a spade, though, it pays to understand why the ground has dropped — because the fix depends entirely on the cause.
Why Do Lawns Sink?
Sunken areas in NZ lawns are common and can result from several causes:
- Soil settlement after construction or landscaping, especially on fill sites
- Organic matter decomposition — buried tree stumps, roots, or old garden waste breaking down underground
- Poor drainage or waterlogging, which causes soil to compact and shift
- Underground pipes or services that have leaked, collapsed, or been poorly backfilled
- Soil erosion from heavy rain, particularly on sloped sections
- Animal activity — burrowing pests or worm activity in soft soils
Identifying the cause is the most important first step. A simple settlement hollow is easy to fix yourself. A depression caused by a leaking pipe or collapsed drain is a different matter entirely.
Check for Underground Services First — This Is Critical
Before you dig anything, you must locate any underground services in the area. New Zealand properties commonly have buried water pipes, stormwater and wastewater drains, electrical cables, and gas lines running through lawns and gardens.
Striking a buried service can be dangerous or fatal. Contact Dial Before You Dig (0800 248 344) to request a service location plan for your property. Your local council may also hold records of drainage and stormwater lines.
If you suspect a sunken area is caused by a broken underground pipe or drain, stop and call a licensed drainlayer or plumber. Work on wastewater and stormwater drains is restricted work under the Plumbers, Gasfitters and Drainlayers Board (PGDB) — it must be carried out by a licensed professional.
Do You Need a Building Consent?
For most straightforward lawn re-levelling — moving small amounts of soil and topping up a hollow — you won't need a building consent. However, if you're planning significant earthworks (for example, cutting or filling significant amounts of material, or work near a boundary or retaining wall), your local council may require consent or at least notification. Always check with your council first. The MBIE Building Performance website has useful guidance on what work requires consent under the Building Act.
Tools and Materials You'll Need
- Spade and garden fork
- Wheelbarrow
- Lawn levelling rake or landscape rake
- Straight-edged board or long spirit level
- Topdressing mix — a blend of sandy loam and compost suited to your lawn type
- Lawn seed or turf to patch bare areas
- Garden roller (optional, can be hired)
For larger areas, hiring a rotary hoe, mini excavator, or plate compactor from a local hire centre will save a lot of effort.
Step-by-Step: How to Re-Level a Sunken Lawn
1. Assess the Depth of the Hollow
Use a straight board and spirit level across the sunken area to measure how far it has dropped. Hollows less than 50 mm deep can usually be fixed with topdressing alone. Deeper depressions may need the turf lifted and soil added beneath.
2. Fix the Underlying Cause
If drainage is poor, consider installing a simple French drain or improving the fall of the ground away from the house before re-levelling. Waterlogged soil will just sink again if you don't address the drainage first.
3. Lift the Turf (for Deeper Hollows)
For depressions deeper than about 50 mm, use a spade to carefully cut and lift the turf in sections. Roll it back like a carpet and keep it moist so it stays alive while you work.
4. Add and Compact Fill
Fill the hollow with a suitable soil mix — a sandy loam or quality garden mix works well in most NZ conditions. Avoid pure clay or subsoil, which compacts poorly and drains badly. Add fill in layers of no more than 100 mm and compact each layer by tamping or rolling before adding the next.
5. Replace the Turf or Reseed
Lay the turf back over the filled area, pressing it firmly into contact with the new soil. Water thoroughly and keep foot traffic off for a few weeks. If the turf is damaged, reseed or lay new turf to match.
6. Topdress and Finish
For shallow hollows, simply spread a topdressing mix across the area, work it into the grass with a rake, and water in well. Repeat over a few seasons if needed for gradual levelling.
NZ Soil and Climate Tips
NZ soils vary enormously — from the heavy clays of Auckland and Waikato to the free-draining volcanic soils of the central North Island and the stony soils of Canterbury. Choose a topdressing mix suited to your region and existing lawn type. Your local garden centre can advise on the best blend. In high-rainfall areas, getting the drainage right is especially important — BRANZ has useful guidance on site drainage and ground conditions.
When to Call a Professional
Call a qualified earthmover or landscaper if:
- The sunken area is large (more than a few square metres) or deep
- You suspect a broken pipe, collapsed drain, or buried organic matter
- The ground is unstable, boggy, or keeps sinking after repair
- The area is near a retaining wall, foundation, or boundary
- You need significant cut-and-fill earthworks
For drainage or pipe issues, you'll need a licensed drainlayer — check the PGDB register. For larger earthmoving or landscaping work, find a qualified local tradesperson on tradedirectory.co.nz.
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