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Skylights are meant to let in extra light, not water!  Added natural sunlight makes your home feel brighter and more spacious, but leaking skylights can take all that beauty away and replace it with rotting structures or mold if you don’t catch them in time.  If you notice a small amount of water leaking out of your skylights, there are several simple ways to troubleshoot and potentially repair the leak.

Double check to make sure that the skylight is fully closed.  Obvious but worth a try.

Verify that the leak is not actually pooled condensation on the underside of the glass.  This happens often in very cold climates, in humid rooms, and with single-glazed skylights.  To reduce condensation, add insulation between the framing members and the skylight itself.  The easiest solution is expanding spray foam.

Look at the area around the skylight from both inside and outside to check for damp or stained surfaces.  Call a professional to do so!

Clear away any leaves, twigs, and dirt that have gathered on the skylight and check the glass itself for cracks.  Seal skylight cracks with a layer of clear silicone along the entire length.

Inspect the Roofing and Flashing Around a Leaking Skylight

Once you’re sure the water is penetrating from the roof outside, look carefully to see if the shingles and flashing around the skylight are properly installed and functional.  Roofing should be firmly nailed down, so repair any lifted shingles.

Next, take a look at the flashing.  Because the purpose of flashing is to make a watertight seal between the skylight and the roof, any visible defects or damage (like corrosion or pinholes) are signs your flashing needs to be replaced.  You should also check that the roofing material extends all the way around the flashing, including each side and the top.  If there is space between the roofing and flashing, water can get trapped and cause leaks.

Seal Flashing Around a Leaking Skylight

Start by clearing any water or debris that has collected between the roofing and flashing. Then lift the roof shingles away from the edges of the skylight so you can access the flashing.  Use a putty knife to add a layer of roofing cement in the gap between the edge of the flashing and the roofing.  This will provide a seal against future leaks, as long as it doesn’t dry out or become brittle.  Check the roofing cement sealant every few months.  If it’s peeling or dried out, remove and apply a new layer.

When the flashing itself is damaged or moldy, it must be replaced.

Condensation

While you’re examining the skylight, look for signs of condensation on the glass.  If you find any, you’ll probably notice it collects at certain points and drips from there.

The best remedy for condensation is ventilation.  If the skylight doesn’t open, consider using a fan to improve air circulation. Clear obstructions from the weep holes, the tiny holes on the lower part of the skylight frame that allow condensation to drain.  This will prevent the skylight glass from clouding up.

Faulty skylight

If the skylight opens, check the rubber gasket around the frame for signs of deterioration or mold.  That would indicate the skylight isn’t sealing all the way and moisture is dripping between the window casing and the frame.  To remedy this, you may need to replace the gasket. You may also find bits of debris preventing the skylight from closing all the way. Removing them may stop the leak.

Your inspection may reveal moisture around a cracked section of the skylight.  Although it may be possible to remove the cracked part and repair it, in most cases you’ll have to replace the entire skylight.

Faulty roof flashing

Once you’ve eliminated condensation and skylight defects, any water you see must be coming through the roof.  It’s either seeping under the flashing or getting through the seal between the flashing and the skylight.

If it’s coming from the frame on the upper part of the roof slope, that’s easier to diagnose and repair than if it’s coming from the lower part of the frame.  Water tends to travel along the roof decking, so a leak from the lower part could originate from anywhere on the roof.  One from the upper part is almost always from the skylight flashing.

Reseal the Flashing

If you determine the water is indeed coming from the flashing, the next step is to go on the roof with a caulk gun and the appropriate sealant.  Sealant should be designed specifically for roof flashing.  Butyl and silicone sealants are not recommended for this project.

The damage may be easy to spot.  You may find parts of the existing sealant have chipped or crumbled away from exposed flashing.  In that case, scrape off all the loose bits with a putty knife and apply a bead of new sealant to the exposed area.

To examine the parts of the flashing that sit flush against the roof, you’ll need to peel back the shingles.  Apply the sealant generously to the edges of the flashing, especially along the head of the skylight on the upper part of the roof.  Remember that any water seeping under the flashing at the top of the skylight can trickle down and drip from a lower part.

You May Need to Reinstall the Flashing

Quality skylights come with flashing, which is leakproof when installed correctly.  Without knowing it, however, a DIY or inexperienced pro installer could damage the flashing by nailing it to the roof.

If you find nails, deteriorated or rusting flashing, or gaps in the step flashing along the sides of the skylight frame where shingles and flashing are layered, it’s probably best to rip up the shingles and redo the flashing.

Hire a vetted contractor.  That way you’ll be sure the proper flashing is used and installed correctly.  It’s an extra expense, but it’s better than doing the job yourself and discovering the skylight still leaks.