Velux skylights, which bring cheery light into a room, are a popular choice in many homes, in both models that open and close and those with a fixed window. While considered one of the best of their type of product, Velux skylights occasionally can suffer from leakage. There are several reasons why leakage takes place.
Check the Roof Pitch
Up until 1996 or so, Velux recommended that its skylights be installed with a pitch of no more than 15 degrees, since increased to 18 degrees. New sealant may be needed, as well as longer screws to hold the skylight in place.
Sometimes, the sealant around the skylight may have cracked a little, allowing water to come in around the edges. A dab of roofing tar along the edges of the seal may stop the leak. If the seal as deteriorated too much, however, it may be necessary to chip it out all the way around the skylight, then apply a new bead of sealant.
Sash May Need Repair
Sometimes, the leak may be occurring around the sash of the skylight window, and a bit of caulking may be in order.
If the skylight appears to be sealed properly, check flashing near the skylight. Any nearby flashing, particularly if it is above the skylight, may lead water to flow down under the shingles and to work its way through thin cracks around the skylight that otherwise would be impervious to water.
When All Else Fails
If minor steps don't solve the problem, major ones may be needed. A reinstallation of the skylight may be needed--or a brand new skylight if the old one has deteriorated to the point it cannot be repaired. Such repairs may be beyond the skills of the average Joe Handyman, and you may need to consider a professional contractor.