Quick Answer
A leaking skylight in a Melbourne home is usually caused by failed flashing, a cracked or degraded seal around the frame, or a broken/cracked glazing panel. Many leaks can be fixed DIY with silicone sealant or flashing tape for $20–$80; a tradesperson repair costs $150–$500 depending on severity. If the frame or glazing is cracked, replacement may be the only lasting fix.
Why Melbourne Skylights Leak
Melbourne’s climate puts skylights through more stress than almost any other Australian city. Temperatures swing from sub-10°C nights in winter to 40°C-plus days in summer, and that thermal cycling expands and contracts aluminium frames and sealants repeatedly. Add frequent strong winds and driving rain from the south-west, and it’s no surprise that skylights rank among the most common roof leak sources our roofing experts see.
The main causes, in order of frequency:
- Failed silicone sealant — the bead around the frame cracks, shrinks, or separates from the substrate after 5–10 years.
- Lifted or corroded flashing — the metal strip that ties the skylight to the roof surface pulls away or rusts through.
- Cracked glazing panel — impact damage (hail is common in SE Melbourne) or UV degradation over 15+ years.
- Condensation mistaken for a leak — warm humid indoor air hitting cold glass; water drips inside but no water enters from outside.
- Blocked drainage channels — some skylights have internal channels that drain to the outside; these clog with debris.
How to Diagnose Your Skylight Leak
Step 1: Determine Whether It’s a True Leak or Condensation
On a dry day, go into the room below and check the ceiling around the skylight for water marks, staining, or damp plaster. If the marks appear only in cold weather and there’s no water entry on wet days, you likely have condensation. Fix: improve ventilation in the room, or consider a double-glazed replacement if the skylight is old.
Step 2: Inspect from Inside During Rain
During the next heavy rain, stand safely below and observe exactly where water is entering. Use a torch to trace the drip path back to the frame. This tells you whether it’s a perimeter seal failure (water enters at the frame edge) or a cracked panel (water enters through the glass or polycarbonate itself).
Step 3: Safe Roof Inspection
Only inspect the roof if you have a safe way to access it — non-slip footwear, dry conditions, and a properly secured ladder. Look for:
- Gaps or separation between the sealant bead and the frame or tiles
- Lifted, bent, or rust-stained flashing strips
- Cracked or yellowed polycarbonate or glass panels
- Debris or moss blocking drainage channels around the frame
DIY Repairs You Can Do Yourself
Reseal the Frame Perimeter
This fixes the majority of skylight leaks. You’ll need: exterior-grade silicone sealant (clear or grey; Selleys WeatherSeal or Bostik Seal & Flex Exterior both work well), a caulking gun, utility knife and sealant remover to strip old sealant, a clean dry rag and methylated spirits.
Process: On a dry, warm day (above 10°C), use the utility knife to cut away all old sealant. Clean the surface with methylated spirits and allow to dry completely. Apply a continuous bead of fresh exterior silicone around the full perimeter of the frame, pressing it firmly into the joint. Smooth with a wet finger. Allow 24 hours to cure before rain exposure. Total cost: $20–$45.
Repair Lifted Flashing
If the metal flashing strip has lifted slightly but is not damaged, you can press it back and re-seal underneath with roofing-grade flashing tape (Flashband or similar) or a compatible roof sealant. For more substantial flashing damage or full replacement, call a licensed roof plumber.
Clear Blocked Drainage Channels
Remove any accumulated leaves, grit, or moss from the channel that runs around the inside of the frame. A stiff brush and garden hose flush will usually clear it. This is a DIY job requiring no special tools.
When to Call a Trades Professional
Some skylight issues go beyond DIY repair:
- Cracked or shattered glazing — a glazier or skylight specialist must replace the panel. Most polycarbonate panels are model-specific; bring the brand and dimensions to your glass supplier.
- Broken or heavily corroded frame — re-caulking a corroded aluminium frame is a temporary fix at best. Frame replacement means full skylight replacement, which requires a licensed roofer in Victoria.
- Full skylight replacement — if the unit is more than 20 years old and leaking repeatedly, replacement is more economical than repeated repairs. A new fixed skylight installed costs roughly $800–$1,500 installed; opening/venting models run $1,200–$2,500.
- Structural ceiling damage — if water has been entering for a prolonged period, ceiling plaster, battens, or insulation may be damaged. A builder should assess before you repair the skylight alone.
Troubleshooting Table
| Problem | Likely Cause | Action |
|---|---|---|
| Drip from centre of glass panel | Cracked or delaminated glazing | Call glazier for panel replacement |
| Water runs down side of frame | Sealant failed at frame edge | DIY: remove old sealant, re-apply exterior silicone |
| Water pooling on inside flange | Drainage channel blocked | DIY: clear channel with brush and hose flush |
| Condensation droplets in cold weather only | Single-glazing, warm humid room | Improve ventilation; or replace with double-glazed unit |
| Leak after recent storm or hail | Impact damage to glazing or flashing lifted | Inspect both; call roofer if flashing is damaged |
Estimated Repair Costs
| Repair Type | DIY Cost | Tradesperson Cost |
|---|---|---|
| Reseal perimeter (silicone) | $20–$45 | $150–$250 |
| Flashing tape repair | $25–$60 | $180–$350 |
| Polycarbonate panel replacement | $80–$200 (panel only; DIY not recommended) | $250–$600 |
| Full skylight replacement (fixed) | Not recommended DIY | $800–$1,500 installed |
| Full skylight replacement (opening) | Not recommended DIY | $1,200–$2,500 installed |
Top 10 Tips and Gotchas
- Never seal on a wet surface. Silicone applied to damp metal or tile won’t adhere and will delaminate within weeks.
- Use exterior-grade silicone, not kitchen/bath grade. Bathroom silicone is not UV-stable and degrades rapidly outdoors.
- Hail is the number-one skylight killer in SE Melbourne. After any hail event, inspect for crazing or micro-cracks in polycarbonate, which become full cracks within a season.
- Don’t ignore small leaks. Even 2–3 drops per downpour will saturate ceiling insulation and rot battens over 12 months.
- Gutter-related leaks mimic skylight leaks. If your skylight is near an eave, clear gutters first — blocked gutters can back water up under tiles near the skylight.
- Check your skylight brand before buying a replacement panel. Velux, Solatube, Fakro, and Chinese aftermarket skylights all use different panel sizes. Bring measurements and photos to your glass supplier.
- Flashband/flashing tape is a temporary fix. It’s useful for a quick patch before a wet forecast, but it degrades under UV within 1–3 years. Don’t rely on it long-term.
- Age check: polycarbonate skylights over 15 years old often have UV-degraded yellowed panels. At this age, sealing around the frame is addressing the wrong problem.
- Licensed roofer requirement: any work that involves removing and re-fastening roof tiles or metal roofing in Victoria legally requires a licensed roofing contractor under the Building Act 1993.
- Check ceiling insulation after a sustained leak. Wet glasswool insulation loses most of its R-value and can take months to dry if left in place. In bad cases, it needs removal and replacement.
Local Melbourne Resources
- Victorian Building Authority — Find a Licensed Practitioner — verify your roofer’s licence before they start
- Bunnings — Exterior Sealants & Adhesives — Selleys WeatherSeal and flashing tape in stock
- Mitre 10 — Sealants & Roof Repair Products — often better range for roofing-specific products
- Velux Australia — Service & Maintenance — if you have a Velux skylight, they have an accredited installer network
Frequently Asked Questions
Can I seal a skylight leak myself without going on the roof?
Sometimes. If the leak is at the inside flange or in a drainage channel you can reach from inside, yes. But most frame seal failures require roof access to address properly. Only access the roof in dry conditions and with appropriate footwear and a secured ladder.
How long does silicone sealant last on a skylight?
Exterior-grade silicone typically lasts 7–12 years in Melbourne conditions, depending on UV exposure and thermal cycling. A north or west-facing skylight will degrade faster. Check the seal every 3 years and reseal at the first sign of cracking.
My skylight leaks only when it’s windy — what’s causing that?
Wind-driven rain enters different pathways than vertical rainfall. The most common cause of wind-only leaks is a small gap between the flashing and the roof surface on the upwind side, or a gap in the frame sealant on the side facing prevailing winds. Inspect both carefully on a dry day.
Is it worth repairing an old skylight or should I just replace it?
If the skylight is under 10 years old and the leak is a simple sealant failure, repair is worthwhile. Over 15 years, especially with yellowed polycarbonate or a corroded frame, replacement is usually more economical — particularly since modern double-glazed skylights significantly reduce heat loss and condensation problems.
How much does a licensed roofer charge to repair a skylight seal in Melbourne?
Expect $150–$300 for a straightforward reseal visit from a licensed roof plumber in Melbourne, including labour and materials. Flashing replacement runs $250–$500. Most roofers charge a minimum call-out of around $120–$150, so it’s worth bundling any other minor roof repairs at the same time.
Final Thoughts
Most Melbourne skylight leaks are fixable with a tube of exterior silicone and a Saturday afternoon — as long as you can safely access the roof and the frame is structurally sound. The key is addressing the root cause: stripping old failed sealant rather than layering new sealant on top, clearing blocked drainage channels, and not dismissing small drips before they become ceiling damage.
If the skylight is over 15 years old, polycarbonate is yellowing, or the frame is corroded, factor replacement cost into your decision. A modern double-glazed skylight costs more upfront but eliminates condensation, retains more heat in winter, and won’t need another reseal job in three years.
