Yes, as a homeowner you can absolutely carry out a basic visual inspection of the weathertightness around your window joinery — no licence is required, and catching problems early can save you thousands of dollars in repairs. That said, a thorough assessment of a leaky building is complex work, and a qualified building inspector should be brought in if you find anything concerning or if your home is at higher risk of weathertightness failure.
Why Weathertightness Around Windows Matters
Windows are one of the most common entry points for water in NZ homes. Poor installation, failed sealants, missing flashings, or inadequate clearances can allow moisture to penetrate the wall cavity, leading to rotting framing, mould growth, and structural damage. The consequences can be serious — both for your health and your home's value. The MBIE Building Performance website has useful guidance on the NZ Building Code's Clause E2 (External Moisture), which sets the standard all window installations must meet.
What You'll Need
- A bright torch or headlamp
- A thin-bladed screwdriver or probe (for gently testing timber firmness)
- A moisture meter (available from Bunnings or Mitre 10 — as a guide, expect to pay roughly $40–$150 for a basic model)
- A ladder (used safely on firm, level ground)
- A notepad or phone to photograph findings
Step-by-Step: How to Inspect Window Joinery Weathertightness
1. Start From the Outside
Walk around the exterior of your home and examine each window carefully. Look for:
- Cracked, missing, or shrinking sealant (silicone or polyurethane) at the junction between the window frame and the cladding
- Gaps or separations between the window reveal and the surrounding wall surface
- Rust staining or streaking below aluminium joinery, which can indicate water tracking
- Missing or poorly lapped flashings above the window head — there should be a continuous head flashing directing water away from the opening
- Cladding damage or staining directly below or beside windows
- Inadequate clearance between the bottom of the window frame and any horizontal surfaces (decks, sills, or apron flashings)
2. Check the Interior
Inside, inspect around every window reveal and sill:
- Look for paint bubbling, staining, or discolouration on the plasterboard or timber lining around the frame
- Check for soft or spongy plasterboard — press gently with your finger
- Use your moisture meter on the wall lining and timber sill. Readings consistently above 16–18% in timber can indicate moisture ingress (check your meter's manual for guidance, as thresholds vary by material)
- Look for mould growth in corners or along the bottom of the frame
- Check that internal sill trims sit flat and haven't lifted or warped
3. Probe Timber Carefully
If you have timber-framed windows or exposed timber reveals, gently probe with a screwdriver. Soft or crumbling timber that the blade sinks into easily is a red flag for rot caused by long-term moisture exposure.
4. Check After Rain
The best time to inspect is during or immediately after heavy rain. Look for active water entry, damp patches appearing on internal linings, or water pooling on internal sills.
Common Risk Factors in NZ Homes
Certain homes carry a higher weathertightness risk. BRANZ research has identified key risk factors, including:
| Risk Factor | Why It Matters |
|---|---|
| Monolithic cladding (e.g. plaster/stucco) | Hides moisture damage; no drainage cavity |
| Low-pitch or complex rooflines | Water can pond near window heads |
| Flush or recessed window joinery | Less protection from wind-driven rain |
| Homes built 1992–2004 | Higher incidence of leaky building syndrome |
| Exposed, high-wind sites | Greater driving rain pressure |
If your home ticks several of these boxes, a professional inspection is strongly recommended.
Maintenance You Can Do Yourself
If your inspection reveals minor issues, some maintenance is well within DIY reach:
- Re-sealing gaps: Remove old, failed sealant fully and apply a quality polyurethane or silicone sealant rated for exterior joinery. Products from Sika are widely used in NZ for this purpose.
- Painting exposed timber: Use a quality exterior primer and topcoat — Resene or Dulux both offer suitable exterior timber systems.
- Clearing debris: Keep window sills, sill trays, and weep holes clear of leaves and dirt that can block drainage.
Note: Re-sealing is maintenance, not building work — no consent is required. However, replacing flashings or modifying the window installation itself may require a building consent or fall under Schedule 1 exemptions. Always confirm with your local council before starting any repair work beyond basic maintenance.
When to Call a Professional
Call a licensed building inspector or LBP (Licensed Building Practitioner) if you find:
- Active water entry or significant moisture meter readings
- Soft, rotten, or damaged framing timber
- Widespread sealant failure across multiple windows
- Any signs of mould inside wall cavities
- A home with monolithic cladding and recessed joinery
- You're buying or selling a property and need a formal report
A professional inspector has specialist tools — including thermal imaging cameras and invasive probes — that go well beyond what a DIY check can reveal. You can find qualified local building inspectors on tradedirectory.co.nz. Check that any practitioner doing remedial building work holds the appropriate LBP licence.
Licensed Building Practitioner (LBP)
BCITO Qualified
