Can I Raise a Sunken Drain Grate to Match New Paving?

Raising a sunken drain grate to match new paving is a common issue when relaying or lifting the level of a driveway, path, or patio. In many cases a homeowner can handle minor adjustments themselves, but some situations require a licensed drainlayer — and getting it wrong can cause flooding, compliance issues, or damage to your drainage system.

Why Drain Grates End Up at the Wrong Height

When new paving is laid over an existing surface — or when old paving is replaced with a thicker product — the surrounding ground level rises while the drain grate stays put. The result is a grate that sits 20–100 mm (or more) below the finished paving surface, creating a trip hazard and a spot where water pools rather than drains away.

What Type of Drain Do You Have?

Before you start, identify your drain type, as this affects both the method and whether the work is restricted:

• Surface channel drains – Long linear drains set into paving. The channel body and grate can often be adjusted or shimmed.
• Stormwater gully pots / sump grates – Round or square grates sitting over a concrete or plastic sump. These are the most common in NZ residential driveways and paths.
• Wastewater gully traps – The grate over a trapped gully connected to your wastewater system. These are restricted work (see below).
• Kerb and channel drains – Council infrastructure; do not touch these without council approval.

What Can a Homeowner Do?

For stormwater surface drains (not connected to the wastewater system), minor raising is generally within a homeowner's capability, provided:

• You are only adjusting the frame and grate height, not cutting or joining pipes.
• The drain body (sump or channel) itself does not need to be moved or replaced.
• No building consent is triggered (check with your local council — most minor drainage adjustments on private property fall under Schedule 1 exemptions, but confirm this).

Common DIY Methods

1. Riser rings or extension collars – Plastic or concrete riser rings are available from plumbing and drainage suppliers. They sit on top of the existing sump body to raise the frame and grate. Make sure the riser is compatible with your sump diameter.
2. Mortar bedding – The existing cast-iron or galvanised frame can sometimes be re-bedded in fresh mortar at the new height. Use a suitable exterior mortar mix and allow full cure time before trafficking.
3. Adjustable grate frames – Some modern channel drain systems have height-adjustable frames built in. Check the manufacturer's instructions.

Key rule: Water must still flow into the drain, not away from it. The finished grate level should sit at or very slightly below the surrounding paving surface — typically 3–6 mm lower — so surface water drains freely.

When Is It Restricted Work?

Under the Plumbers, Gasfitters, and Drainlayers Act 2006, drainlaying work on sanitary drains (wastewater and stormwater drains that connect to the public network) must be carried out by, or under the supervision of, a licensed drainlayer registered with the Plumbers Gasfitters & Drainlayers Board (PGDB).

You must use a licensed drainlayer if:

• The drain grate is connected to the wastewater system (e.g., a gully trap).
• Raising the grate requires cutting, joining, or repositioning pipes.
• The sump or drain body itself needs to be raised or replaced.
• The drain connects to the public stormwater network and the work involves more than surface-level adjustment.
• Your council requires an inspection or building consent for the work.

If you are unsure whether your drain is stormwater or wastewater, check with a licensed drainlayer or your local council before starting. Connecting incorrectly can cause serious contamination issues and may breach the NZ Building Code (particularly clauses E1 Surface Water and G13 Foul Water).

Step-by-Step: Raising a Stormwater Sump Grate (DIY)

1. Remove the grate and frame – Lift carefully; cast-iron frames are heavy.
2. Clean the top of the sump – Remove old mortar, debris, and dirt.
3. Measure the height difference – Calculate how much you need to raise the frame to sit 3–6 mm below finished paving level.
4. Install riser rings or mortar bed – Use riser rings for larger adjustments; mortar for fine-tuning. Ensure the riser is level.
5. Re-seat the frame – Bed the frame in mortar or secure per the riser manufacturer's instructions. Check it is level in all directions.
6. Allow to cure – Keep foot and vehicle traffic off until mortar is fully set (typically 24–48 hours minimum).
7. Replace the grate – Confirm it sits flush or just below the paving surface and that water flows toward it.

Matching Grate Style to Your Paving

If you are upgrading paving, it is a good opportunity to replace an old or rusty grate with one that suits the new surface. Options include galvanised steel, stainless steel, and polymer grates in various load ratings. Check load ratings if the drain is in a driveway — pedestrian-rated grates are not suitable for vehicle traffic.

When to Call a Professional

Call a licensed drainlayer if:

• You are not certain whether the drain is stormwater or wastewater.
• The sump or pipe needs to be physically moved or replaced.
• The height difference is large and requires structural changes to the drain body.
• Your council requires inspections or consent.
• You simply want the job done correctly and to code the first time.

A qualified local drainlayer can assess the situation quickly and ensure the work meets the NZ Building Code and any council requirements. You can find licensed drainlayers in your area on tradedirectory.co.nz.

Safety note: Always check for underground services before digging around any drain. Call Before U Dig (0800 248 344) to locate cables and pipes.

Sources & Further Reading

• Plumbers Gasfitters & Drainlayers Board – Licensed Drainlayers
• MBIE Building Performance – NZ Building Code
• BRANZ – Drainage and Stormwater Guidance
• WorkSafe NZ – Safe Excavation and Underground Services
• Mitre 10 – Drainage Products
• Bunnings – Drainage and Grates