Keeping roof water away from your foundation is one of the most effective things you can do to protect your home from moisture damage, subsidence, and costly repairs. The good news is that many surface-level water management tasks are well within a confident DIYer's reach — but some work is legally restricted to a licensed drainlayer, so it pays to know the difference before you start digging.
Why Foundation Water Damage Is a Serious Problem
New Zealand's variable climate — from heavy Auckland downpours to Christchurch's clay-heavy soils — means poorly managed stormwater can quickly saturate the ground around your foundations. Over time this leads to soil erosion, foundation movement, damp subfloors, and even mould growth inside the home. Under the NZ Building Code, clause E1 (Surface Water) requires that stormwater is managed so it doesn't damage buildings or neighbouring properties, so getting this right matters both practically and legally.
Step 1 — Check Your Gutters and Downpipes First
Before doing anything at ground level, start at the roof. Blocked or undersized gutters are the most common reason water ends up pooling near foundations.
- Clean gutters at least twice a year (more often if you have overhanging trees).
- Check that gutters fall toward the downpipe — a spirit level will confirm this.
- Inspect downpipe joints for leaks and make sure every downpipe has a proper shoe (the angled fitting at the bottom) directing water away from the house.
- Extend downpipe shoes with a splash block or a flexible downpipe extender so water discharges at least 600 mm–1 m away from the foundation wall.
Splash blocks and downpipe extenders are inexpensive and available at Bunnings or Mitre 10. This alone can make a significant difference.
Step 2 — Improve Surface Grading Around the House
Surface grading (the slope of the ground around your home) is your first line of defence. The ground should slope away from the foundation at a minimum fall of about 50 mm over the first 1–2 metres.
- If the ground slopes toward the house, you can add topsoil or compacted fill to build up the level and redirect surface runoff.
- Avoid piling soil directly against timber weatherboards or cladding — maintain the clearances required by your cladding manufacturer and BRANZ guidelines.
- Compact the fill well so it doesn't settle unevenly over time.
This is straightforward DIY work requiring only a shovel, wheelbarrow, and a long straight-edge or level.
Step 3 — Install a Surface Channel or Swale
For larger volumes of water or sloped sections, a surface swale (a shallow, gently graded channel in the lawn) or a surface drain channel can intercept runoff before it reaches the foundation.
- A swale is simply a shallow depression graded to carry water to a safe discharge point — a legal road channel, your council's stormwater system (check your local council's rules first), or a soakage area on your own property.
- Plastic channel drains with grates can be set into paving or concrete paths and connected to a downpipe or directed to a safe outlet. Cutting and laying these surface channels is generally DIY-friendly.
- Always check with your local council before discharging to any public drain or waterway — rules vary by region.
Step 4 — Consider a Simple Soakage Pit or Rain Garden
If your soil drains reasonably well, a soakage pit (a gravel-filled hole that allows water to percolate into the ground) or a rain garden (a planted depression that absorbs runoff) can handle downpipe discharge without connecting to any underground drainage system.
- Soakage pits should be located at least 1.5–3 m away from the foundation and away from boundaries (check your council's requirements).
- They work best in free-draining soils — clay-heavy soils may need a different approach.
- A rain garden planted with moisture-tolerant NZ natives is an attractive, low-maintenance option.
Neither a soakage pit nor a rain garden involves connecting to the underground drainage network, so they generally don't require a licensed drainlayer or a building consent — but always confirm with your local council before proceeding, as rules differ.
What Work Is Legally Restricted to a Licensed Drainlayer?
This is where many homeowners get caught out. Under the Plumbers, Gasfitters, and Drainlayers Act 2006, drainlaying work — which includes installing, altering, or connecting to any underground stormwater or wastewater drainage system — is restricted work that must be carried out or supervised by a registered and licensed drainlayer.
Specifically, you must use a licensed drainlayer if you want to:
- Connect a new underground stormwater pipe to the council's public drain or your property's existing underground drainage network.
- Install or alter underground perforated agricultural drain (ag-drain) systems.
- Lay underground pipes that form part of the property's drainage system.
Doing this work yourself is illegal and could void your home insurance, create issues when you sell, and potentially cause serious drainage problems for neighbours.
When to Call a Professional
Call a licensed drainlayer if:
- Surface fixes haven't solved the problem and you suspect water is tracking through the soil to your foundations.
- You need to connect any underground pipe to the council's stormwater system.
- You're dealing with persistent damp subfloors, which may indicate a failed agricultural drain or high groundwater.
- Your property has significant slope or complex drainage issues.
A licensed drainlayer can also advise whether a building consent is required — some drainage work falls under Schedule 1 exemptions, but this depends on scope and your local council's interpretation. Always check with your council.
You can find qualified, local drainlayers on tradedirectory.co.nz.
Sources & Further Reading
- MBIE Building Performance — Building Code clause E1 Surface Water
- Plumbers, Gasfitters and Drainlayers Board — licensing and restricted work
- BRANZ — moisture and drainage guidance
- Bunnings NZ — drainage and stormwater products
- Mitre 10 NZ — drainage and landscaping supplies
- Energywise — healthy, dry homes
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