Yes, in most cases you can identify failing joinery seals yourself without any specialist tools. A methodical walk-around inspection — both inside and outside your home — will reveal the most common warning signs. Catching seal failure early is important in New Zealand's varied climate, where wind-driven rain can quickly turn a minor gap into a serious moisture problem.
Why Joinery Seals Matter
Joinery seals — including sealants, gaskets, weatherstripping, and flashings around windows and doors — form the first line of defence against water ingress and draughts. When they fail, moisture can penetrate wall cavities, leading to rot, mould, and structural damage. Under the NZ Building Code, Clause E2 (External Moisture) requires buildings to prevent moisture from causing undue dampness or damage, so keeping seals in good condition is not just good practice — it's part of maintaining a compliant home.
What You'll Need for Your Inspection
- A torch or headlamp
- A thin, flat tool (like a butter knife or feeler gauge)
- A piece of tissue or thin paper
- A garden hose (optional, for a water test)
- A notepad or your phone to photograph problem areas
Step 1 — External Visual Inspection
Start outside on a dry day. Work your way around every window and door frame, looking for:
- Cracked, shrinking, or missing sealant — silicone and polyurethane sealants harden and pull away from surfaces over time, especially on north-facing elevations exposed to UV.
- Gaps between the joinery frame and the cladding — even a 1–2 mm gap can allow significant water entry under wind pressure.
- Discolouration or staining on cladding below windows, which can indicate water is tracking down from a failed seal.
- Rust streaks from aluminium joinery fixings, suggesting moisture is getting behind the frame.
- Damaged or missing flashings above windows and doors — these are critical for diverting water away from the frame.
On James Hardie fibre cement or timber weatherboard cladding, pay particular attention to the junction between the cladding and the window reveal, as this is a common failure point. See James Hardie for guidance on correct detailing around their products.
Step 2 — Internal Visual Inspection
Move inside and check around every window and door:
- Paint bubbling, peeling, or staining on the interior reveals or surrounding walls — a classic sign of moisture getting in.
- Mould or mildew on or near the frame, particularly in corners.
- Soft or spongy timber around the sill or reveal — press gently with your thumb. Solid timber should feel firm; softness suggests rot from prolonged moisture exposure.
- Condensation patterns — if condensation consistently forms at the same spot on a frame (not just the glass), the seal or thermal break may be compromised.
Step 3 — The Paper (Draught) Test
For doors and openable windows, the paper test is a quick way to check weatherstripping and compression seals:
- Close the door or window on a piece of paper or tissue.
- Try to pull the paper out.
- If it slides out easily with little resistance, the seal is not compressing properly and needs attention.
Repeat this at several points around the frame — top, sides, and bottom — as seals often fail unevenly.
Step 4 — The Water Hose Test (Optional)
If you suspect a specific area is leaking but can't see obvious damage, have a helper run a garden hose gently over the outside of the joinery while you watch from inside for any water entry. Start low and work upward so you can pinpoint the source. Do not use high pressure — you're simulating rain, not a pressure washer.
Common Seal Types and Their Failure Signs
| Seal Type | Where Found | Common Failure Signs |
|---|---|---|
| Silicone/polyurethane sealant | Frame-to-cladding junction | Cracking, shrinkage, pulling away |
| Foam weatherstripping | Door/window rebates | Compression loss, tearing, gaps |
| Rubber gaskets | Aluminium joinery | Hardening, cracking, displacement |
| Head flashings | Above frames | Lifting, corrosion, missing sections |
| Sill flashings | Below frames | Ponding, blocked drainage slots |
What to Do If You Find a Problem
Minor sealant gaps on accessible, single-storey joinery are generally straightforward for a competent DIYer to address — clean out the old sealant, prepare the surface, and apply a quality exterior-grade sealant such as those available from Sika or products stocked at Bunnings or Mitre 10. Always follow the manufacturer's preparation instructions for a lasting bond.
For more complex issues — failed flashings, rot in structural framing, or joinery that needs replacing — you'll want professional help. Refer to BRANZ for best-practice guidance on weathertightness repairs.
When to Call a Professional
Call a Licensed Building Practitioner (LBP) or a qualified building inspector if you find:
- Soft or rotten framing timber around multiple windows
- Evidence of water in wall cavities (staining low on interior walls, musty smells)
- Failing flashings that require removal and reinstallation
- Any joinery that may need replacing, as this can trigger building consent requirements — always check with your local council first
- You're unsure of the extent of damage
A professional building inspector can carry out a moisture meter survey and thermal imaging to find hidden damage that a visual check will miss. You can find qualified local building inspectors and tradespeople on tradedirectory.co.nz.
For Healthy Homes compliance (relevant to rental properties), draught stopping is a specific requirement — see Tenancy Services for the current standards.
Licensed Building Practitioner (LBP)
BCITO Qualified
