Yes, checking whether your internal walls are out of plumb is absolutely something a homeowner can do themselves — no special licence required. With a few basic tools and a methodical approach, you can get a clear picture of how vertical your walls are and whether the issue warrants a closer look by a professional building inspector.
What Does 'Out of Plumb' Mean?
Plumb simply means perfectly vertical — straight up and down. A wall that is out of plumb leans or bows to one side. Minor variations are common in older NZ homes, particularly those built before modern framing standards like NZS 3604 were widely adopted. However, significant or worsening lean can signal foundation movement, framing failure, or moisture damage — all worth investigating.
Tools You'll Need
You don't need expensive equipment. Here's what works well:
- Spirit level (1.2 m or longer is ideal for walls)
- Plumb bob (a weighted string line — cheap and highly accurate)
- Long straightedge or timber batten (to detect bowing mid-wall)
- Tape measure
- Pencil and notepad to record readings
How to Check Your Walls Step by Step
1. Use a Spirit Level
Hold your spirit level vertically against the wall surface. The bubble should sit centred between the lines. Check at the top, middle, and bottom of the wall, and in multiple spots across its width. Note which direction the bubble moves — this tells you which way the wall leans.
2. Use a Plumb Bob
For greater accuracy, especially on tall walls, hang a plumb bob from a nail or pin at the top of the wall. Let it settle, then measure the gap between the string and the wall surface at the top and bottom. If the gap is different, the wall is out of plumb by that difference.
3. Check for Bowing
A wall can be plumb at the top and bottom but still bow outward or inward in the middle. Run a long straightedge or taut string line horizontally across the wall to check for this.
4. Record Your Measurements
Use a simple table like this to track your findings:
| Wall Location | Top Gap (mm) | Bottom Gap (mm) | Difference (mm) | Notes |
|---|---|---|---|---|
| Lounge north wall | 0 | 8 | 8 | Leans outward |
| Hallway east wall | 2 | 2 | 0 | Plumb |
| Bedroom south wall | 0 | 15 | 15 | Investigate further |
What's an Acceptable Tolerance?
NZS 3604, which covers timber-framed buildings, sets out construction tolerances for framing. As a general guide, a deviation of up to around 5 mm over a 2.4 m wall height is typically considered within acceptable limits for new construction. Older homes may have more variation due to age, settlement, or original build quality — this doesn't always indicate a structural problem, but anything beyond about 10–15 mm of lean deserves further investigation. Always check with a qualified professional rather than relying solely on your own assessment.
What Could Cause a Wall to Be Out of Plumb?
Common causes in NZ homes include:
- Foundation settlement or movement — particularly relevant in areas with expansive soils or earthquake activity
- Subfloor timber rot or pile failure — common in older NZ homes with timber piles
- Moisture damage to framing, often linked to weathertightness issues covered under MBIE's Building Performance guidance
- Original construction variation — especially in pre-1970s homes
- Earthquake damage — even minor events can shift framing over time
Warning Signs to Watch For
Beyond the lean itself, look for these red flags:
- Cracks in GIB plasterboard lining, especially diagonal cracks at door and window corners
- Doors or windows that stick, won't latch, or have uneven gaps around frames
- Gaps appearing between the wall and ceiling or floor
- Visible bowing or bulging of the wall surface
- A lean that appears to be getting worse over time
When to Call a Professional
If you find walls that are noticeably out of plumb — particularly more than 10–15 mm — or if you notice any of the warning signs above, it's time to bring in a qualified building inspector or Licensed Building Practitioner (LBP). They can assess whether the issue is cosmetic, age-related, or a sign of something more serious like foundation failure or structural framing damage.
A professional inspector has the tools, training, and experience to interpret what they find in the context of your whole home — not just one wall. This is especially important if you're buying or selling a property, or if you suspect earthquake damage. You can find qualified local building inspectors on tradedirectory.co.nz.
For anything involving structural repairs to framing, you may need a building consent from your local council. Some work may qualify as exempt under Schedule 1 of the Building Act, but always confirm this with your council before starting — MBIE Building Performance has useful guidance on what requires consent.
Licensed Building Practitioner (LBP)
BCITO Qualified
