How to repair a leaking skylight due to improper installation or flashing failure.
A skylight is often considered a valuable addition to a home, but it is often the case that a skylight can be a liability due to poor installation, seal failure, or damage. There are a number of different factors that can lead to a leaking skylight but the most common factor is an improperly sized or installed skylight. Typically water stains are found on the drywall around the skylight for slight leaks and during rain or snow storms, you may see an active leak dripping from the skylight. Depending on the construction of your roof, the leak may be several feet away from the source of the leak. Also, whether the skylight is operable or fixed, there are several sources for potential leaks.
Skylight leak with drywall damage
It is important to understand how skylights are installed and to have a working knowledge of your roofing system.
Cutaway of Skylight
Skylight with Curb
Causes for Skylight Leaks
Any hole or crack in the skylight head or counter flashing can lead to leakage around the skylight and the roof shingles. Age, extreme weather conditions and damage due to falling tree limbs can also be the cause of your leaky skylight. For leakage where the skylight meets the roof shingles, the leaks are usually found at the top corners. For roofs with a low pitch, snow can accumulate at any point and the leakage can occur near the bottom of the unit.
An improperly constructed curb can also be a source of leakage, even if the skylight and flashing was installed properly.
Not all water stains are cause by water entering around the skylight from the outside. Condensation can form on the inside of skylight glass panels due to excessive moisture inside the home caused by improperly vented clothes dryers, washing machines, cooking, dishwashers, and bathing. The problem may not become evident until the outside temperature drops below freezing. Ice or snow accumulations on the outside of your skylight will accelerate the formation of condensation on the inside of your skylight. A failed seal between insulated glass in double glazed skylights will allow any moisture to condense between the panes of glass. To correct condensation you will need to make sure that any exhaust fans in the home are used when necessary and working properly
Damage from leaking Skylights
A leaky skylight may only cause minimal damage at first, but the longer the leak is allow to remain, the damage can become significant. Even with condensation, it is possible that carpeting or furniture may be damaged along with the expected paint and drywall repairs. However structural damage may occur due to rot and mold and mildew may grow on the wood framing. Wet insulation will also increase heating and cooling costs as well as shorten the life of roof sheathing and shingles.
As a general rule, any roof leak should be repaired as soon as possible whether the repairs are performed by the home owner or a professional roofer.
Repairing Skylight Flashing
If you have determined that your skylight leak is not caused by condensation, you will have to inspect and repair the flashing around the perimeter of the unit. You can purchase repair kits for skylights, or contact the manufacturer for any technical support and parts. In many cases it is easier to remove the shingles around the curb to repair or replace the flashing.
Remove the window portion of the skylight. These are typically held in place with screws and clips along the sides of the unit. Next pry off the old shingles, carefully pulling nails to save the flashing. As long as the flashing is installed in the correct sequence, from the bottom to the top, you should have a leak-proof skylight when you’re finished.
You will need a hammer, pry bar, screwdriver, utility knife, flashing kit, and 1 ½ inch roofing nails.
Install adhesive underlayment
Install 6-in.-wide strips of a self-sticking waterproof underlayment. This underlayment will direct any water that may get through the metal flashing onto the roofing felt. Install from the bottom up, lapping each piece on top of the lower one.
Set the lower flashing
Set the bottom one-piece flashing on top of the shingle course. Nail it only at the upper corners into the side of the curb, not the roof. Make sure that the lower flashing is sitting on top of the shingles at the bottom of the skylight.
Install step flashing
Alternate step flashing and shingles along the side of the skylight. Nail at the upper corner.
Set the head flashing
The head flashing is one piece that wraps around the sides. This fabricated piece has welded and sealed seams and corners. Fit and install the next row of shingles, leaving about 1/2 in. of flashing exposed.
Install any remaining shingles that were removed to install the skylight flashing.