Can I Replace a Cracked Fibreglass Skylight Dome Myself?

Replacing a cracked fibreglass skylight dome is a job many confident Kiwi homeowners can tackle themselves, provided the existing skylight frame and kerb (the raised surround) are in good condition and no structural or weatherproofing work is required beyond swapping the dome. That said, working at height carries real risk, and some situations do call for a licensed roofer.

What's Involved in a Dome Replacement?

A fibreglass skylight dome sits in a pre-formed plastic or timber kerb that is fixed to the roof structure and flashed to keep water out. When only the dome itself is cracked — not the kerb, flashing, or surrounding roofing — replacement is usually straightforward:

1. Remove the retaining ring or clips holding the dome in place.
2. Lift out the old dome.
3. Clean the seating surface and check the kerb for damage or UV degradation.
4. Drop in the new dome (same size and profile).
5. Refit the retaining ring and apply fresh sealant if required.

No building consent is generally needed for a like-for-like dome replacement that doesn't alter the size, location, or weatherproofing system — but always confirm this with your local council, as Schedule 1 exemptions under the NZ Building Code can vary. You can check guidance at MBIE Building Performance.

Measuring and Sourcing the Right Dome

Before you buy anything, measure carefully:

• External kerb dimensions (length × width, or diameter for round domes)
• Dome profile height (low-profile vs. high-rise)
• Glazing thickness if it's a double-skin dome

Take photos of the existing dome, kerb, and retaining system to your supplier. Replacement domes are available from roofing merchants and hardware stores such as Bunnings or Mitre 10, or direct from skylight suppliers. Common NZ brands include Velux and Solatube, though many older homes have generic fibreglass domes — match the profile as closely as possible.

Do You Need a Building Consent?

A straight like-for-like replacement of a dome (same size, same position, no structural changes) is generally exempt from building consent under Schedule 1 of the Building Act 2004. However, if you're changing the size of the opening, altering the kerb, or modifying the roof structure, consent is likely required. Always check with your local council before starting — rules can vary by region and by the type of roof cladding involved. See MBIE Building Performance for general guidance on consent exemptions.

Safety First — Working at Height

This is the most important part. Falls from roofs are a leading cause of serious injury in New Zealand. WorkSafe NZ sets clear expectations around working at height, even for homeowners doing their own maintenance.

Before you climb up:

• Never work on a wet, frosty, or windy day.
• Use a properly footed ladder that extends at least 1 metre above the eave.
• Wear non-slip footwear.
• Have a second person on the ground to steady the ladder and pass materials.
• On steeper pitches (generally over 25°), consider hiring a roofer — it's not worth the risk.
• Do not walk directly on fibreglass or polycarbonate roofing panels; they may not support your weight.

Weatherproofing — Getting It Right

The NZ Building Code Clause E2 (External Moisture) requires that roofs and their penetrations keep water out. A poorly sealed skylight dome can cause significant water damage over time. When fitting the new dome:

• Use a neutral-cure silicone sealant rated for roofing and UV exposure (check the manufacturer's datasheet — products from Sika are widely used in NZ roofing applications).
• Do not use standard household silicone, which can degrade quickly outdoors.
• Check that the existing flashing around the kerb is intact and properly lapped under the roof cladding. If the flashing looks damaged or corroded, stop and call a roofer.
• Inspect the kerb itself for cracks, UV chalking, or rot (on timber kerbs). A damaged kerb needs professional attention before a new dome is fitted.

What If the Kerb or Flashing Is Damaged?

If the kerb is cracked, the flashing is lifting, or there are signs of water staining on the ceiling below, the job goes beyond a simple dome swap. Kerb replacement and reflashing involve cutting into the roof cladding and ensuring the weatherproofing meets the Building Code weathertightness requirements. This work is best left to a qualified roofer who understands your specific roof type — whether it's corrugated iron, long-run steel, concrete tiles, or another cladding. You can find experienced local roofers on tradedirectory.co.nz.

When to Call a Professional

Call a licensed roofer if:

• The kerb, flashing, or surrounding roof cladding is damaged.
• You're not comfortable working at height or the roof pitch is steep.
• The skylight is on a multi-storey building.
• You're unsure whether consent is required.
• Water has already entered the ceiling space — there may be hidden damage to insulation, framing, or lining that needs assessment.
• The existing dome is a non-standard size or integrated into a more complex roofing system.

A qualified roofer can also advise whether upgrading to a double-skin dome (better insulation, less condensation) is worthwhile — a smart consideration given New Zealand's Healthy Homes standards and the push for warmer, drier homes.

Sources & Further Reading

• MBIE Building Performance — Building Consent Exemptions
• WorkSafe NZ — Working at Height
• Sika NZ — Sealants and Adhesives
• BRANZ — Roof Penetrations and Weathertightness
• Tenancy Services — Healthy Homes Standards
• Bunnings NZ — Roofing Supplies