Skylight leaks are one of the more frustrating roofing problems NZ homeowners face, especially in our wet, wind-driven climate. The good news is that minor maintenance — like resealing exposed flashings or refreshing sealant — is something a competent DIYer can tackle. However, more significant waterproofing work, particularly anything involving structural changes to the roof or replacing flashings, will likely require a licensed professional and possibly a building consent.
Understanding Why Skylights Leak
Before reaching for the sealant gun, it pays to understand what's actually causing the leak. Common culprits include:
- Failed or cracked sealant around the skylight frame or kerb
- Deteriorated or poorly installed flashings — the metal strips that bridge the skylight frame to the surrounding roofing material
- Condensation dripping inside, often mistaken for a roof leak
- Cracked or damaged glazing on the skylight unit itself
- Blocked or inadequate drainage around the skylight kerb
Identifying the true source of the leak is critical. If water is only appearing after heavy rain with wind, it's likely a flashing or sealant issue. If it appears in cold weather regardless of rain, condensation may be the culprit. Check BRANZ for guidance on diagnosing moisture problems in NZ homes.
What the NZ Building Code Says
Skylight waterproofing sits under Clause E2 (External Moisture) of the NZ Building Code, which requires roofs and their penetrations to prevent water ingress. Any work that changes the weathertightness of your roof — including replacing flashings or modifying the skylight kerb — may require a building consent. Always check with your local council before starting, as Schedule 1 exemptions are limited when it comes to roof penetrations. See MBIE Building Performance for consent guidance.
DIY Waterproofing: What You Can Safely Do
For minor maintenance, a capable homeowner can:
Refresh Sealant Around the Frame
- Clean the area thoroughly — remove old, cracked sealant with a scraper and clean the surface with a suitable solvent.
- Choose the right product — use a high-quality, UV-stable, paintable polyurethane or silicone sealant rated for roofing applications. Sika offers roofing sealants widely available in NZ. Check the manufacturer's data sheet to confirm suitability for your roofing material (metal, tile, membrane, etc.).
- Apply carefully — run a neat, continuous bead and tool it into the joint. Avoid bridging gaps wider than the product's recommended span.
- Allow full cure time before exposing to rain.
Apply a Waterproofing Membrane Coat
If your skylight sits on a flat or low-pitch roof with a membrane surface, you may be able to apply a compatible liquid waterproofing membrane around the kerb. Products from Ardex or Mapei include membrane systems suitable for this purpose — always follow the manufacturer's instructions and ensure compatibility with the existing membrane.
Safety First on the Roof
Working at height carries serious risk. Always:
- Use a properly secured ladder and, where possible, roof anchor points
- Avoid working on wet or frosty roofs
- Never work alone
- Check WorkSafe NZ guidelines for working at height before you start
What You Should NOT Do Yourself
Some skylight waterproofing work goes beyond DIY:
- Replacing or modifying metal flashings — this is skilled trade work and, if done incorrectly, can void warranties and cause significant damage
- Relocating or resizing a skylight — this is restricted building work requiring a Licensed Building Practitioner (LBP). See LBP
- Re-roofing around the skylight — any significant roofing work should be done by a qualified roofer
- Electrical connections on powered or solar-operated skylights — this is restricted electrical work and must be carried out by a registered electrician. See EWRB
Choosing the Right Products
| Product Type | Suitable For | NZ Supplier |
|---|---|---|
| Polyurethane sealant | Frame-to-roof joints, kerb edges | Sika, Bunnings, Mitre 10 |
| Liquid waterproofing membrane | Flat/low-pitch membrane roofs | Ardex, Mapei |
| Butyl flashing tape | Temporary repairs, underlap sealing | PlaceMakers, Bunnings |
Always read the product data sheet and confirm the product is compatible with your specific roofing material before purchasing.
When to Call a Professional
If you've refreshed the sealant and the leak persists, it's time to call a qualified waterproofer or roofer. You should also call a professional if:
- The flashings are corroded, bent, or missing
- The skylight kerb is cracked or structurally compromised
- Water damage has spread to ceiling linings, insulation, or framing
- You're unsure of the leak source
- The roof pitch or access makes working safely impossible
A licensed waterproofer or roofer will carry the right insurance, understand NZ Building Code compliance, and can provide a producer statement if required. You can find qualified local waterproofing tradespeople on tradedirectory.co.nz.
Site Safe
SiteWise
Licensed Building Practitioner (LBP)
