Yes, you can absolutely carry out a basic visual inspection of your own foundation — and it's a smart habit to do so regularly. However, while a DIY check is a great first step, interpreting what you find correctly is where things get tricky. Some cracks are harmless; others signal serious structural problems. This guide walks you through what to look for, how to document it, and when to bring in a qualified professional.
Why Foundation Checks Matter in New Zealand
New Zealand's geology makes foundation health particularly important. We sit on an active tectonic boundary, meaning earthquake movement, soil settlement, and expansive clay soils are common concerns across the country. Add in our variable rainfall and the prevalence of older timber-framed homes on shallow foundations, and it's clear why keeping an eye on your foundation is worthwhile.
The NZ Building Code sets out structural performance requirements, and foundations must meet these standards throughout the life of a building — not just at the time of construction.
What You'll Need for a DIY Inspection
You don't need specialist equipment for a basic check. Gather:
- A torch (head torch is ideal)
- A tape measure or ruler
- A notepad or your phone for photos
- A piece of chalk or masking tape to mark cracks
- Knee pads if you're crawling under the house
How to Inspect Your Foundation Step by Step
1. Walk the Perimeter
Start outside. Walk slowly around the entire exterior of your home, looking at the foundation walls, piles, or concrete slab edge. Look for:
- Cracks — note their direction, length, and width
- Bulging or bowing walls
- Gaps between the foundation and the framing above
- Efflorescence — white chalky deposits that indicate moisture movement through concrete
- Crumbling or spalling concrete
2. Check the Subfloor Space (If Applicable)
Many NZ homes — particularly those built before the 1980s — are on timber piles with an accessible subfloor. If yours has a crawl space:
- Enter carefully and use your torch to inspect timber piles for rot, splitting, or leaning
- Look for piles that have sunk, shifted, or lost contact with the bearer above
- Check for moisture, pooling water, or signs of fungal growth
- Look at the condition of the ground — soft, wet, or disturbed soil can indicate drainage issues
Safety note: Before entering a subfloor space, check for hazards including asbestos insulation (common in homes built before the mid-1980s), rodents, and poor ventilation. If in doubt, don't enter — contact a professional. WorkSafe NZ has guidance on working safely around asbestos.
3. Inspect Interior Floors and Walls
Foundation movement often shows up inside the house first. Look for:
- Sloping or bouncy floors — place a marble on the floor and see if it rolls
- Sticking doors or windows that have recently become hard to open or close
- Diagonal cracks running from the corners of door and window frames
- Cracks in wall linings or ceiling plasterboard
4. Document Everything
Photograph every crack and mark its ends with chalk or tape and the date. Check back in four to six weeks. Cracks that grow or widen over time are a red flag and should be assessed by a professional promptly.
Understanding What Cracks Mean
Not all cracks are equal. Use this as a rough guide:
| Crack Type | Likely Cause | Action |
|---|---|---|
| Hairline cracks (under 0.2 mm) | Normal concrete shrinkage | Monitor over time |
| Horizontal cracks in concrete block walls | Lateral soil or water pressure | Get professional assessment |
| Diagonal stair-step cracks in masonry | Differential settlement | Professional assessment needed |
| Vertical cracks, uniform width | Concrete shrinkage or minor movement | Monitor; check for water ingress |
| Wide cracks (over 3 mm) or growing cracks | Significant movement | Urgent professional inspection |
BRANZ is New Zealand's building research authority and publishes useful guidance on building defects and maintenance that can help you understand what you're seeing.
Limitations of a DIY Inspection
A homeowner inspection is a visual check only. You cannot assess:
- Subsurface soil conditions or bearing capacity
- Reinforcing steel inside concrete (and whether it's corroding)
- Pile depth and embedment
- Compliance with NZS 3604 (the timber-framed buildings standard) or site-specific engineering requirements
- Earthquake damage that may not be visible on the surface
If your home has been through a significant earthquake, even if it looks fine, a professional inspection is strongly recommended.
When to Call a Professional
Call a Licensed Building Practitioner (LBP) or a qualified building inspector if you notice:
- Any crack wider than 3 mm or that is actively growing
- Horizontal cracks in foundation walls
- Floors that slope noticeably or have become worse over time
- Piles that are visibly leaning, rotting, or have lost contact with bearers
- Water consistently pooling around or under the foundation
- Doors or windows that have recently started sticking for no obvious reason
- Any concerns after an earthquake
For structural concerns, you may also need a Chartered Professional Engineer (CPEng) to assess the foundation and provide a report. Your building inspector can advise whether this is necessary.
You can find qualified local building inspectors and LBPs on tradedirectory.co.nz. Always check that any LBP you hire is currently registered at lbp.govt.nz.
If you're buying or selling a property, a pre-purchase building inspection by a qualified inspector is highly recommended — foundation issues can be costly to remediate and may affect your ability to get insurance or a mortgage.
Licensed Building Practitioner (LBP)
BCITO Qualified
