Skylight Dripping in Winter? Condensation vs. a Real Leak

You wake up on a frosty January morning and there's water dripping from the skylight. It's natural to assume the roof is leaking. Often it isn't. In a Massachusetts winter, the most common cause of a wet skylight is condensation, and the fix has nothing to do with the roof. Here's how to tell the difference, and what to do about each.

Quick Summary

• Water on the inside of the glass on a cold, dry morning is almost always condensation, not a leak.
• A leak shows up after rain or snowmelt, usually as stains on the drywall around the opening or drips from the frame edges.
• Condensation comes from indoor humidity meeting cold glass. Exhaust fans, lower humidity and moving air usually fix it.
• VELUX suggests keeping indoor humidity around 30 to 40% on typical Massachusetts winter days, and lower in deep cold.
• Real leaks come from failed flashing, failed seals, ice dams backing up behind the skylight, and age.
• Repair or replace depends on the skylight's age, its glass, and whether a roof replacement is coming. Doing both together means new flashing and one disruption.

The Short Answer: How to Tell in 30 Seconds

Ask yourself four questions:

1. Has it rained or has snow been melting in the last day or two? If not, a leak is unlikely.
2. Where is the water? Droplets spread across the inside of the glass point to condensation. Water at the frame edges or on the drywall around the opening points to a leak.
3. When does it show up? Condensation is worst on the coldest mornings and after showers, cooking or laundry.
4. Are there stains? Brown rings or peeling paint on the drywall of the opening usually mean water has been getting in from outside.

Still not sure? Wipe the glass dry and look again the next cold morning. If it's wet again on a dry day, it's condensation.

Condensation vs. Leak: Side-by-Side Signs

• When it appears: Condensation shows up on cold mornings and after showers or cooking, whether or not it rained. A leak shows up during or after rain, or when snow on the roof is melting.
• Where the water is: Condensation is spread across the inside of the glass and frame. A leak is at the frame edges, corners or the drywall around the opening.
• Stains: Condensation rarely stains unless it has dripped for a long time. A leak often leaves brown rings, bubbling paint or soft drywall.
• Pattern: Condensation gets better when humidity drops or the weather warms. A leak repeats with each storm or thaw.
• Rooms most affected: Condensation hits bathrooms, kitchens and bedrooms with doors closed. A leak can show up in any room.
• Who fixes it: Condensation is usually the homeowner, sometimes with a roofer's help. A leak needs a roofer.

Why Skylights Sweat in a Massachusetts Winter

Warm air holds moisture. When it touches a cold surface, that moisture turns back into water. A skylight is usually the coldest surface in the room, and it sits at the highest point, where warm, humid air collects. That makes it the first place condensation forms.

The usual causes:

• High indoor humidity. Breathing, showers, cooking, laundry and humidifiers all add moisture. Newer, tighter homes trap more of it, as VELUX points out.
• Old glass that insulates poorly. Older double-pane units without low-E coatings run much colder on the inside.
• An uninsulated light shaft. Where the skylight opening passes through a cold attic, uninsulated shaft walls chill the air around the glass.
• Air leaks around the frame. Gaps let warm, moist air reach cold parts of the frame.

VELUX publishes a simple guide for winter humidity at 70°F indoors. Above these levels, condensation will form on any cold surface, not just skylights:

• 10°F to 20°F outdoors: 35 to 40% indoor humidity
• 0°F to 10°F outdoors: 30 to 35% indoor humidity
• -10°F to 0°F outdoors: 25 to 30% indoor humidity
• -20°F to -10°F outdoors: 20 to 25% indoor humidity

How to Reduce Skylight Condensation

What you can do:

• Run bathroom fans during showers and for a while after, and use the kitchen hood when cooking.
• Turn down or turn off humidifiers on very cold days, and check humidity with an inexpensive hygrometer.
• Run a ceiling fan on low to keep air moving across the glass.
• Keep shades open when you can, so warm room air reaches the glass.
• If you have a venting skylight, open it for a few minutes on a dry day to let moist air out.
• Make sure your dryer vents outdoors.

What a roofer can do:

• Insulate and air seal the light shaft where it passes through the attic.
• Seal gaps around the frame from the interior and exterior.
• Replace an old unit with a modern skylight that has low-E glass and better seals. See our VELUX skylights page for current options.

Our 7 Most Common Winter Roofing Problems post covers attic condensation too. It's often the same moisture problem showing up in a different place.

When It Really Is a Leak, and What Causes It

If the water lines up with rain or melting snow, the skylight is letting water in. The most common causes:

• Failed flashing. The metal that ties the skylight into the roof corrodes, loosens or was installed wrong. Our roof flashing guide explains how it fails.
• Failed seals or gaskets between the glass and frame.
• Ice dams. Snow melts, refreezes below the skylight, and backs water up under the flashing. Learn how to stop them in our ice dam guide.
• Age. Skylights commonly last 15 to 40 years, depending on type and installation, but seals and flashing often wear out first.

We see this pattern often. A homeowner in Blackstone had leaking skylights and a ventilation problem that were fixed in the same job. In Franklin, we repaired a leaking skylight by replacing the sheathing around it, installing GAF underlayment and re-shingling for a watertight seal.

Repair or Replace Your Skylight?

Repair usually makes sense when:

• The skylight is less than about 10 to 15 years old.
• The glass is clear and the problem is flashing or a single seal.
• The roof around it has plenty of life left.

Replace when:

• The glass is fogged between the panes. That means the seal has failed, and it can't be repaired.
• The skylight is near the end of its typical life, or it's a plastic dome.
• You're replacing the roof soon. This is the big one. A new skylight gets new flashing tied into the new underlayment and shingles. Replacing the skylight later means tearing into a brand-new roof.

We've replaced skylights along with the roof in Holliston, Sherborn, Upton and Westwood, plus projects in Lexington and Charlestown.

A note on taxes: the federal tax credit for ENERGY STAR skylights ended for anything installed after December 31, 2025. See Is a New Roof Tax Deductible in Massachusetts? for what still applies.

Want more light without a full skylight? A sun tunnel brings daylight into hallways and bathrooms through a smaller roof opening.

Not Sure What You're Seeing? We'll Check It

Master Roof is a VELUX-trained skylight installer serving MetroWest and the I-495 corridor. If your skylight is dripping and you can't tell why, contact us for a free inspection. We'll tell you whether it's condensation you can fix yourself, a repair, or time for a new skylight. Learn more about our skylight installation and repair services.

Frequently Asked Questions