Map where the water shows up
Start inside, from the floor, with a torch. Note whether water is coming from the edge of the diffuser, from inside the diffuser itself, from the ceiling beside the opening or from a mark some distance away. Each points to a different part of the assembly. Drips from the diffuser edge often mean water is running down the light well. A stain on the ceiling a metre downhill of the skylight may mean water entered at the roof opening and travelled along a rafter or batten before reaching plaster.
Mark the uphill side of the skylight on a quick sketch of the room. On most roofs the uphill edge is where debris collects and where the flashing has to divert the most water around the opening. If the stain sits on the downhill side, it does not rule out the uphill edge, because water runs down the outside of the upstand and the light well before it appears. The sketch saves the roofer time and stops the conversation starting with a guess.
Keep a record of the weather each time water appears. Rain with a strong wind from one direction, a long soaking rain and a short heavy downpour stress different parts of the flashing. A skylight that leaks only in westerly storms may have a problem on one side, while one that leaks after every shower suggests something more general such as a cracked dome or a blocked uphill section. Photograph the diffuser and ceiling each time from the same spot.
Know the parts that can let water in
A fixed skylight or roof window is usually set on an upstand or kerb that raises the glazing above the roof surface. A flashing kit wraps the upstand and laps under or over the roof covering so water is carried around the opening. The glazing, whether glass, acrylic or polycarbonate, sits in a frame with its own seals. Below the roof, a light well or shaft runs down to a diffuser at ceiling level. The Australian Government Your Home guide on skylights and roof windows describes these types and the choices in glazing and light wells.
A tubular skylight is simpler in appearance but has the same logic: a dome on the roof, a flashing collar around a tube, and a reflective tube or flexible duct running down to a ceiling diffuser. Leaks at a tubular unit commonly involve the collar and its seal to the roof covering, a dome that has cracked or lost its seal, or a tube joint that lets outside air and moisture into the roof space. Each of these can deliver water to the same diffuser.
Finally, the roof covering around the opening matters. On a tiled roof, tiles are cut and fitted around the upstand and the flashing is dressed onto them. A tile broken while someone worked on the skylight, or one that has slipped, can let water under the flashing. On a metal roof, the sheet around the opening is cut and the flashing is fixed and sealed to the ribs. A problem in the sheet, the fixings or the sealant can look exactly like a failed skylight.
| What you see | Part to check first | Question to ask the roofer |
|---|---|---|
| Drips from the diffuser edge during rain | Flashing and upstand, then light well joints | Where does water first reach the light well? |
| Water inside the dome or light well on cold mornings | Condensation, light well insulation and seals | Are the external parts sound so we can treat this as condensation? |
| Stain on the ceiling downhill of the skylight | Uphill flashing and nearby tiles or sheets | Which route did the water take along the framing? |
| Leak only in wind from one direction | Flashing on that side, cut tiles or sheet edges | Can you show the gap on the exposed side in a photograph? |
| Cracked, crazed or yellowed dome | Glazing and frame seals | Is a replacement dome available, or does the unit need replacing? |
Tiled and metal roofs fail around skylights differently
On a tiled roof, look for the uphill side first. Leaves, seed pods and grit collect behind the upstand where the flashing turns the water. When that area fills, water can back up and spill over the flashing edge, especially in heavy rain. Cracked mortar or broken tiles next to the opening are also common after someone has walked around the skylight. A roofer will usually lift the tiles around the upstand to see the flashing and the underside, which is not something to try yourself.
On a metal roof, the typical issues are the fixings through the flashing, sealant that has shrunk or lost adhesion, and the flashing shape where it crosses the ribs. If a flashing does not follow the rib profile closely, the gap is often packed with sealant, which ages faster than the metal. Water can also enter at screws in the sheet near the skylight, which is covered in our guide to metal roof screw leaks. Ask the roofer to check the sheet and the fixings around the opening, not only the skylight frame.
Older homes around Toowoomba may have a skylight added long after the roof was laid, sometimes during a renovation, sometimes by a previous owner. That matters because the flashing may have been improvised rather than supplied as a kit for that roof. If you have the product name or installation paperwork, include it. If you do not, say so. The roofer can then judge whether the flashing can be repaired or whether it needs a replacement kit made for the unit and roof profile.
Rule condensation in or out
Not every wet skylight is a leak. A light well passes through the roof space, which can be much colder or hotter than the room below. On cold mornings, moist indoor air can condense on the inside of the dome or the light well and drip back onto the diffuser. This is more likely above bathrooms, laundries and kitchens, and in homes where the light well is not insulated or sealed at the ceiling. Your Home notes that skylights, like windows, can be a major source of heat loss in winter.
The simplest test is timing. Water that appears on dry, cold mornings and disappears by midday points towards condensation. Water that appears during or just after rain points towards rain entry. Some homes have both. Record dry days as well as wet ones. If you only write down the bad days, the pattern is hard to see. Our roof condensation guide explains how to keep a short moisture diary that a roofer can use.
If condensation is the likely cause, sealing the outside of the skylight will not fix it. The conversation shifts to the light well: whether it is insulated, whether the diffuser seals to the ceiling, whether a vented unit is venting, and how moist the room is. A roofer can check the external parts and confirm they are sound, then you can deal with ventilation and the light well with confidence that you are not also chasing a rain leak.
Reseal, reflash or replace the unit
Resealing makes sense when the flashing and glazing are sound and a specific sealant joint has failed. It is a small repair, but it should be done on a clean, dry surface with a sealant suited to the materials. Ask the roofer to show you the failed joint in a photograph. If the answer is to run sealant around the whole skylight, ask why each section needs it. Blanket sealing can trap water that the flashing is meant to drain.
Reflashing is the right choice when the flashing is damaged, poorly shaped, rusted or never suited the roof. On a tiled roof this usually means lifting tiles, fitting a new flashing kit and relaying the tiles. On a metal roof it may mean replacing the flashing and some fixings, and sometimes a short length of sheet. It costs more than resealing, but it removes the reason sealant kept failing.
Replacing the unit is worth discussing when the dome is cracked, crazed or yellowed, when the frame has deteriorated, when the skylight leaks and also causes summer heat or winter heat loss, or when parts are no longer available. Some owners decide to remove a skylight altogether and have the roof and ceiling closed over. That is a legitimate option if the room has other light. Ask for the options to be priced as separate lines so you can compare them properly.
Keep off the skylight and the roof
Skylights are a known fall hazard. The glazing is not designed to take a person's weight, and on a roof it can be hard to see, especially a dome that has faded or collected dirt. Never step on a skylight or lean on it, and do not climb onto the roof to look at one. A photograph from the ground or from a window is enough for a first conversation. Roofers use fall protection and plan their access around fragile areas.
Inside, the diffuser is usually clipped or screwed to the ceiling frame. Removing it to look up the light well can seem harmless, but a wet ceiling around it may be weak, and some diffusers sit near downlights or wiring. If water is near a light fitting, keep people clear and do not touch the fitting. Leave the diffuser in place unless the maker's instructions say otherwise and the ceiling is dry and sound.
If a skylight is broken, for example after a hail storm or a falling branch, treat it as an urgent opening. Keep people out of the room below. Move belongings or place containers only from a safe position, away from unstable ceilings, broken glazing and electrical equipment. A roofer can make it safe with a temporary cover until the unit is replaced. Our storm leak guide covers the first 24 hours after that kind of damage.
Hypothetical example: a hallway tubular skylight
A family in Highfields has a tubular skylight in a windowless hallway. After a stormy week, water drips from the diffuser onto the floorboards. They assume the dome has cracked. Their notes show drips on two wet evenings with strong westerly wind and nothing on still, wet days or on cold mornings. They send the roofer a sketch showing the skylight is on the western roof slope, a photograph of the dome taken from the backyard, and the dates.
On inspection, the dome is intact. The roofer finds that the collar flashing has lifted slightly on the uphill side and that a tile beside the collar has cracked. In a westerly, rain is driven under the collar and runs down the outside of the tube to a joint near the ceiling. The quote lists replacing the cracked tile, resetting the collar flashing and checking the tube joints from the roof space, with photographs of each step. It does not include a new skylight because nothing points to the unit itself.
The useful part of this example is the order: record, describe, inspect, then decide. Had the family replaced the dome first, the leak would have continued. Had the roofer only run sealant around the collar, the cracked tile would still have let water through. The record kept the repair focused on what the evidence showed.