New Build Cracks: What’s Normal vs Structural? NZ Homeowner Guide 2025

You spot a crack on a fresh wall and your stomach drops. Is your new home already failing, or is this just the building settling in? Here’s the straight answer for New Zealand homes in 2025: many tiny cracks in the first 3-12 months are normal and fixable, but a few patterns mean call someone now. I’ll show you how to tell the difference, how to measure and track them, and when to push for repairs under your warranty. I live in Wellington, so I’m writing with seismic and wind in mind.

• TL;DR: Hairline cracks under ~0.2 mm are common in the first year. Note them, wait for one full season cycle, then get them touched up at your 12‑month defects visit.
• Cracks 0.2-1 mm: monitor and photograph. Ask your builder to make-good at the first-year check.
• Cracks over 1-2 mm, stepped cracks in brick or blockwork, repeating cracks across door heads, or anything growing fast: call your builder now; consider a structural engineer if movement continues.
• In NZ, you have a 12‑month defects repair period for residential work under the Building Act, plus 10‑year implied warranties. Use them.
• After earthquakes or slips, lodge with your insurer promptly; EQC (Toka Tū Ake) may be involved for building damage.

What’s normal in the first year of a new build?

New houses move. Timber dries, concrete shrinks, seasons swing, humidity drops when you turn on heating, and the whole frame finds its long-term shape. In Wellington, you can add wind racking and the occasional shake. That early movement shows up as small cracks, mostly cosmetic.

Typical first-year cracks you might see:

• Hairline lines at plasterboard joints and internal corners.
• Tiny gaps at skirting, scotia, and window architraves.
• Fine crazing in paint films, especially on sun-baked walls.
• Hairline meanders in slab-on-ground garages or driveways.

Why it happens:

• Drying shrinkage: Timber framing and plasterboard compounds lose moisture and contract after you move in and heat the home. NZS 3604 assumes framing moisture falls after lock-up.
• Concrete shrinkage: Slabs shrink as they cure; control joints help, but hairlines still happen.
• Seasonal movement: Wet winter to dry summer can move cladding and timber by a millimetre here and there.
• Seismic and wind: Even small shakes or strong northerlies can highlight weak points like door heads and ceiling junctions.

What counts as “normal”? A practical rule-of-thumb that aligns with MBIE tolerances guidance and common industry practice:

• Hairline cracks under ~0.2 mm (a pencil line) in interior plaster: normal cosmetic settlement.
• Fine cracks 0.2-1 mm in plaster or paint: common. Monitor and request touch-ups within the defects period.
• Cracks 1-2 mm: borderline. Often fixable with stopping and repainting, but track for growth.
• Over 2 mm, or cracks that open/close through the day, or that repeat across multiple rooms: investigate now.

New Zealand context that matters:

• Defects period: For most residential contracts here, you get a 12‑month defects repair period. The Building Act implies the builder must fix defects notified in that window. Many owners batch small crack repairs for that visit.
• Implied warranties: The Building Act 2004 gives you up to 10 years of implied warranties for workmanship and materials. If a crack points to poor work or movement from insufficient control joints, you have rights well beyond 12 months.
• Guarantees: Master Build and HALO guarantees typically cover structural issues long-term; cosmetic cracks are usually a first-year item.

Industry references: MBIE’s tolerances guidance for residential work expects minor shrinkage cracks; BRANZ guides call these common and fixable; NZS 3101 and related concrete guidance aim to limit crack width for durability, but domestic slabs still show hairlines even with best practice. You shouldn’t see ongoing growth across multiple elements.

Measure and monitor: simple ways to size cracks and track movement

You don’t need fancy gear. A few everyday items will give you a reliable read on size and change over time.

Quick sizing hacks:

• Mechanical pencil lead: 0.5 mm or 0.7 mm. If the crack is narrower than the lead, you’re under that size.
• Credit card: about 0.76 mm thick. If a crack swallows the edge, you’re around the 0.7-1.0 mm zone.
• Printer paper: roughly 0.1 mm thick. If it just slides in, you’re near hairline territory.
• Fingernail test: if you can barely catch it, think ~0.2-0.3 mm.

How to document:

1. Photograph with a ruler or a coin in frame. Keep the same angle and distance each time.
2. Log it: room, location (e.g., north wall by kitchen window), date, estimated width.
3. Mark discreetly: a tiny pencil dot at each end lets you see if it grows.
4. Repeat after big weather swings, a quake you felt, and before your 12‑month inspection.

Decision tree (use this like a flowchart):

• Is the crack under ~0.2 mm and not spreading? Note it. Request cosmetic repair at the 12‑month defects visit.
• Is it 0.2-1 mm? Photograph, log, watch across one season. If stable, add to defects list for stopping and repainting.
• Is it over 1 mm, or are doors/tiles/windows nearby binding or popping? Notify your builder now. Ask for a site check.
• Is it stepped through masonry, diagonal from window corners, repeating across multiple rooms, or appearing after a quake? Builder plus a structural engineer’s opinion is worth it.

Pro tips that save time:

• Turn on raking light (a torch held along the wall). You’ll see what a normal ceiling light hides.
• Note humidity. A dehumidifier can shrink timber and widen cracks for a week or two; don’t panic-check again after conditions stabilise.
• If a crack opens and closes with daily temperature, you’re looking at movement, not failure. The fix is flexible compounds and proper jointing, not just paint.

Fix or wait? The right remedy and timing under NZ warranties

Most cosmetic cracks get sorted at the end-of-first-year tidy-up. The goal is to let the house complete one full wet-dry cycle before you spend money or use your one “free” visit.

Common fixes (what your builder or stopper will do):

• Interior plaster hairlines: Scrape, apply fibre-reinforced compound or setting compound, sand, repaint that wall or the room for an even finish.
• Corner cracks: Add paper/fibre tape and setting compound to bridge movement, not just skim and hope.
• Gaps at trims: Low-shrink decorators’ caulk, then paint.
• Tile grout: Rake out and regrout with a flexible grout. In showers, check waterproofing if cracks are recurring.
• Exterior plaster hairlines: System-approved sealers or elastomeric coatings; sometimes a proper control joint is needed if the original detailing missed one.

When to bring forward repairs:

• If water can get in (exterior cladding, window heads, parapets), do not wait. Water beats warranties every time.
• If a crack keeps growing month on month, fix the cause first. Cosmetic patches won’t last.
• If doors won’t latch or floors feel different, you may have movement beyond “cosmetic.”

Your rights and how to use them (NZ specifics):

• 12‑month defects repair period: For residential building work, the Building Act gives you a one-year period where notified defects must be fixed by the contractor. Put issues in writing with dates and photos.
• 10‑year implied warranties: Work must be done with reasonable skill, suitable materials, and be fit for purpose. These warranties are automatic. If a crack points to poor design or workmanship (say, missing control joints), you can pursue a remedy beyond 12 months.
• Guarantees: If your build is covered by a Master Build or HALO guarantee, check what’s cosmetic vs structural. Use their dispute process if needed.

Timing matters. I usually tell owners to compile a defects list at month 10-11: you’ve seen the first winter/summer swing, and you have buffer to schedule trades. If you’re in Wellington and had a notable quake during that first year, note the date so the builder understands context.

DIY or not?

• DIY is fine for tiny interior hairlines: a tub of fine filler, a 120/180 grit sanding pad, and leftover paint. If you see mesh tape under paint, it’s already been bridged-don’t yank it.
• Do not DIY exterior cladding cracks unless you’re following the cladding system’s details. Wrong sealant traps water.
• Leave anything near wet areas, balustrades, or structural elements to the pros.

Red flags and who to call in Wellington and across NZ

Most cracks won’t make the evening news. But some patterns are worth acting on straight away-especially in quake country.

Call now if you see:

• Stepped cracks in brick or block veneer, especially radiating from corners or lintels.
• Diagonal cracks running from window or door corners across plasterboard.
• Horizontal cracks at mid-height of walls, or multiple rooms showing the same line.
• Slab cracks wider than ~2 mm, or cracks that offset vertically (one side higher).
• New gaps under skirting plus doors suddenly rubbing-movement is happening.
• Any crack that lets water in, or staining around it.

Earthquakes and storms: what’s different?

• After a felt quake, cosmetic cracks can spike. Note them, take photos, and check for alignment changes (doors, windows). If you suspect structural movement, call a structural engineer.
• Insurance: Report quake or landslip damage to your insurer promptly; they coordinate with Toka Tū Ake EQC for the building cover portion. Keep your photos and dated notes.
• Hillsides: Wellington homes on cut-and-fill or retaining walls deserve extra attention. Cracks coupled with deck posts tilting or fences leaning need swift eyes on site.

Who to call, in order:

1. Your builder or site supervisor: Start a written defects note with photos and measurements. Ask for an onsite review and suggested remedy.
2. Professional stoppers/painters (for cosmetic only): If you’re outside the defects period and it’s small stuff, a good stopper will fix and finish in a day.
3. Structural engineer: If there’s repeating cracking, stepped masonry, slab offsets, or changes after a quake. Ask for a brief assessment first; it’s cheaper and fast.
4. Your insurer: For quake, landslip, or storm related cracking that may be more than cosmetic. They’ll guide EQC steps.

Checklist: crack triage you can do today

• Measure: use the credit card or pencil trick and note the size.
• Photograph with scale and date stamp.
• Check for function changes: sticky doors, windows, uneven floors.
• Look outside for matching signs: paving or paths tilting, brick mortar stepping.
• Decide: wait for defects visit, notify builder now, or bring in an engineer.

FAQ (quick hits)

How much is too much cracking in a new build? Hairlines under ~0.2 mm are common. Anything over 1-2 mm, repeating across the home, or growing fast needs attention.

Are ceiling cracks normal? Hairline cracks at ceiling joints or where scotia meets plasterboard are common in the first year. Wide lines, sags, or repeated cracks along truss lines need a look.

Will paint fix it? Paint hides, it doesn’t bridge movement. Use fibre tape and setting compound on joints, then repaint. Elastomeric paint can help on exterior plaster-only if the system allows it.

Do earthquakes void my builder’s obligations? No, but quake-related damage is an insurance route. If a quake exposed a weak detail (say, missing control joints), discuss both with your builder and insurer.

When should I schedule repairs? Month 10-12 is perfect for cosmetic interiors. Exterior cracks that risk water should be handled immediately.

Can central heating or a dehumidifier cause cracks? Rapid drying can make hairlines show up sooner. Run heating and dehumidifiers steadily rather than “blast and forget.”

Next steps / troubleshooting for different scenarios

• If you’re inside 12 months: Start a defects list now. Group cosmetic fixes for one efficient visit. Include dates, sizes, and photos.
• If you’re past 12 months but within 10 years: If you believe a design or workmanship issue is causing cracks, write to the builder citing the Building Act implied warranties. Consider an independent report to support your case.
• If you felt a quake and saw new cracks: Photograph immediately, check doors and windows, and log a note with your insurer if damage seems beyond cosmetic. Ask your builder to inspect.
• If you’re on a hillside: Walk the outside. Look for new gaps at retaining walls, fence leans, or paving steps. Combine those observations with interior cracks to decide on an engineer visit.
• If you’re selling: Disclose, but also fix what’s cosmetic. A tidy stopping and repaint can defuse buyer nerves, and an engineer letter (if you needed one) reassures everyone.

Final tip: don’t let the first hairline freak you out. New homes settle. Use a simple measuring habit, document changes, and use the NZ warranty framework you already paid for. If something feels off, get a pro pair of eyes. Most of this is simple, fix-once-and-forget sort of stuff.

If you need a one-sentence sanity check: most new build cracking you’ll see in the first year is normal and cosmetic, and the system here in NZ is set up to put it right.