Why skylights leak after a re-roof

How flashing keeps rain out

Flashing is the metal fitted around a roof opening to guide rain past it. Around a skylight, the pieces overlap with the surrounding roofing so water can keep moving down the slope. The lower piece sheds onto the covering below, the side pieces fit between courses and the upper detail directs runoff around the opening.

That arrangement has to be fitted in the right order while the roof around the unit is accessible. A bead of sealant on the surface cannot replace missing or incorrectly overlapped flashing. Sealants have a place in specified details, but adding another layer without inspecting the assembly can hide the cause of a leak. When discussing a repair, ask what will be uncovered and how the flashing will connect with the existing roof. You do not need to know the name of every metal piece. You do need an explanation of how the proposed work will get water past the opening and back onto the roof below it.

What changes during roof replacement

A re-roof removes the material around the skylight, even if the unit stays where it is. The new covering may have a different thickness or profile from the old one. Flashing that suited the previous roof needs to be checked against the new material, and damaged or unsuitable pieces need attention while the area is open.

A leak may not become visible until the first substantial rain after the job. Note when it appeared, where the water showed indoors and whether the wind was blowing from a particular direction. Those observations can help someone investigate, but they do not prove which detail failed. It is also worth asking whether the unit or flashing was replaced, what product was used and what was retained. Photographs taken during the work can be helpful if they are available. Treat the timing as a reason to inspect the new work carefully, rather than assume that an older skylight must suddenly need replacing or that the roofer is automatically at fault.

Check the frame beneath the unit

Many older skylights sit on a raised wooden frame called a curb. The flashing wraps around it and the unit rests above it. The wood needs to be sound, and the curb needs to suit the skylight and finished roof. Replacing the glass or outer frame alone will not put damaged supporting wood right.

Roof replacement is a useful time to assess the curb because the surrounding material is removed. If the new layers change the height of the finished roof, the clearance around the skylight also needs checking. Ask whether the curb was inspected and whether any changes were included in the estimate. If it now needs work, the repair may require reopening roofing around the unit. That is why a quote for a replacement skylight should distinguish the unit from the carpentry and flashing beneath it. A clear scope helps you compare estimates and avoids discovering partway through the job that the visible skylight was only one part of what needed attention.

Who to contact and what to ask

Start with the contractor who carried out the roof work. Explain when the leak began and ask for an inspection of the skylight detail and the roof above it. Keep the estimate, warranty and any photographs together. Water can travel before it becomes visible indoors, so the inspection should not stop at the edge of the stain.

Ask what the findings show before agreeing to a new unit. If the glass and frame are sound, the appropriate job may concern the flashing or curb instead. If the unit has failed, the estimate should explain the replacement and the surrounding roof work it needs. Our VELUX installation and flashing carries 10 years leak-free; the written warranty sets out the coverage and its conditions. That term is not evidence of what caused a particular leak, and it is not the same as a glass-seal warranty. Have the contractor identify the applicable coverage and explain any proposed repair in writing so you can decide on the work with the diagnosis in front of you.