Winter Skylight Condensation, Frost, and Snow: What NH Homeowners Should Know
If you have a skylight in New Hampshire, you have probably wiped condensation off it in January. Maybe you have watched frost creep across the interior glass in a February cold snap. Maybe you have stood at the bottom of the stairs during a Nor’easter, looking up at snow-covered skylight glass, and wondered how much weight it can actually hold.
Winter is when skylight owners either learn to love their skylights or convince themselves to remove them. And the frustrating thing is that a lot of the horror stories out there — “skylights always leak,” “they turn your bedroom into an icebox” — are hangovers from 1980s bubble skylights, not the modern VELUX units we install today.
Here is what is actually normal, what is a real problem, and how modern skylights are built to handle a New Hampshire winter.
Why Condensation Forms on Skylights (and Why It Is Not a Leak)
Here is the physics. Your indoor air holds moisture — from cooking, showering, breathing, houseplants, humidifiers. Warm air holds more moisture than cold air. When that warm, moist air rises (which it does — hot air rises, and skylights are at the top of the room), it hits the coldest surface in the room. That surface is almost always your skylight glass.
When the air touches the cold glass, it cools rapidly. Cool air cannot hold as much moisture as warm air. The excess moisture condenses out as water droplets on the glass surface.
This is not a leak. It is basic physics, and it happens with every window in your house — you just notice it on skylights because the glass is above your head and the water pools before dripping.
The variables that drive skylight condensation:
- Indoor humidity. The higher your indoor humidity, the more condensation. Homes with humidifiers, lots of houseplants, or families that shower without running exhaust fans see the most.
- Outdoor temperature. Colder outside = colder glass = more condensation.
- Rooms with stagnant air pool moisture near the ceiling. Rooms with good circulation do not.
- Glass performance. Older skylights with clear or basic insulated glass condense more. Modern low-E argon-filled units condense far less.
When Condensation IS a Problem
Most winter condensation is annoying but harmless. Wipe it off, run the bath fan longer, done. But there are four signs that your condensation has crossed the line from “physics” to “something to fix.”
1. Water Dripping Consistently
Occasional wiping is normal. Water dripping onto the floor day after day means your indoor humidity is dangerously high (usually 55%+ in winter), or your skylight’s insulating unit has failed.
2. Interior Frame Staining
If you see brown or gray staining on the drywall around the skylight opening (the “shaft”), water has been pooling and running down the frame for a while. That is a signal to inspect the flashing outside and address the humidity inside.
3. Ice Buildup Inside the Frame
Frost on the glass is normal in extreme cold. Actual ice at the corners of the frame or between the glass panes means the IGU seal has failed — the argon gas has escaped, moisture is inside the sealed unit, and the skylight needs replacement.
4. Mold at the Edges
Black spotting on the perimeter caulk or drywall means chronic moisture. This one needs both a humidity fix and a professional inspection of the skylight and shaft.
What About Snow on the Skylight?
Every winter, someone calls us convinced their skylight is going to collapse under a snow load.
The reality: modern curb-mounted VELUX skylights are engineered for the snow loads NH delivers, and then some. VELUX products are tested and certified for structural loads that far exceed the ground snow load ratings — 60 to 120 psf — seen across the White Mountains and Lakes Region.
That said, three snow situations do warrant attention.
Deep Drifted Snow on a Shallow-Pitch Skylight
If your skylight is on a low-pitch or nearly flat section of roof, blown snow can drift several feet deep. That is when it is worth calling a professional to clear it — not because the glass will break, but because meltwater from that much snow can find its way past even well-flashed skylights.
Snow That Stays for Weeks
Blocks natural light (obvious) and can build heavier layers of compacted, refrozen snow. Same drainage risk as above.
Ice Buildup at the Perimeter
If ice dams form on the roof around the skylight, meltwater backs up under the flashing. This is really an ice dam problem, not a skylight problem, but it presents as a skylight leak. (See our post on heated roof systems if this describes your house.)
Do NOT climb onto your roof to clear snow off a skylight. Skylights are strong from above but you are not landing on them evenly. Every year, homeowners fall through skylights they were trying to clear. Use a roof rake from the ground, or call us.
The “Cold Zone” Underneath: Why Old Skylights Feel Drafty
If you have a skylight installed before 2000, chances are the room beneath it feels 3 to 5°F colder than the rest of the floor in winter. That is not your imagination — it is the same physics that drives condensation, but you are feeling it as a downdraft of cold air pouring off the glass.
Old skylights had:
- Single-pane or basic double-pane glass (U-factor 0.60 to 0.80)
- Aluminum frames that conducted heat straight outside
- Minimal or no low-E coating
- Air-filled cavities (no argon)
Modern VELUX skylights have:
- Low-E argon-filled double or triple-pane glass (U-factor as low as 0.19)
- Thermally broken frames
- Warm-edge spacers that eliminate cold perimeter bridging
- Optional laminated inner pane for sound and safety
The comfort difference is dramatic. Homeowners who replace a 1990s bubble skylight with a modern VELUX unit consistently tell us the room “feels warmer everywhere,” not just under the skylight.
Old Bubble Skylights vs Modern VELUX: Why It Matters
If you moved into a NH home built between 1975 and 2000, your skylights are probably plastic “bubbles” — domed acrylic or polycarbonate units mounted directly to the roof deck with minimal flashing.
These are the reason skylights got a bad reputation. Bubbles yellow with UV exposure, crack from freeze-thaw cycles, leak at every seam, and offer almost no insulation value.
A modern flashed VELUX curb-mounted skylight is a fundamentally different product. It uses tempered glass, three-layer engineered flashing, laminated inner panes for safety, and comes with a 10-year installation warranty when installed by a certified pro.
We remove and replace old bubble skylights every year, especially on metal roof re-roofs where the old skylight has to come off anyway. If your skylight is a bubble, it is not really a question of if it should be replaced — it is when.
What to Do This Winter
Whether your skylight is new or 30 years old, three things to do before deep winter.
1. Control Indoor Humidity
Target 30 to 40% relative humidity. Buy a $15 hygrometer from any hardware store and check the reading in the room with the skylight. If it is above 45%, run exhaust fans longer, check that your humidifier is not overcompensating, and open bedroom doors during the day to circulate air.
2. Inspect After the First Big Storm
After the first sustained snow (usually early December in central NH), take a look at the drywall around each skylight from inside. Any new staining or discoloration means water made it past the flashing during that first storm — call us before the next one.
3. Plan Replacement for Spring, Not Emergency
If your skylight is a bubble, more than 20 years old, or showing seal failure (fogging between panes, ice inside the frame), start planning a spring replacement now. Getting on our schedule in the fall for a May install is much easier than trying to book in April.
Frequently Asked Questions
Should I close curtains or shades on my skylight at night in winter?
Yes, if you have interior blinds. It creates an insulating air pocket and reduces both heat loss and condensation. VELUX makes cellular blinds specifically designed for their skylights.
Do solar-powered venting skylights help with condensation?
Significantly. A venting unit lets you exhaust moist air directly out the top of the room, which is exactly where humidity accumulates. Solar VELUX units run on a small internal battery charged by a rooftop panel — no wiring required, and the unit closes automatically if it senses rain.
Do sun tunnels have the same condensation issues?
No. Sun tunnels are a closed reflective system with a small acrylic diffuser at the ceiling, so warm indoor air does not reach a cold surface the same way. If you want daylight without the winter condensation question, a sun tunnel is often a better choice.
Is condensation covered under warranty?
No — condensation is a physics and humidity issue, not a product defect. Seal failure (moisture inside the sealed pane) is a warranty issue on most VELUX products for 10 years.
Can you replace a skylight in the middle of winter?
We prefer not to for weather-tightness reasons, but it is possible in emergencies. Better plan: schedule now for a spring replacement.
How long do modern VELUX skylights last?
The glass unit typically lasts 20 to 25 years. The frame and flashing much longer with proper installation. When a modern skylight needs work down the road, it is usually a glass unit replacement, not a whole-unit tear-out.
Talk to a VELUX Certified Installer
FBI Contracting is a VELUX Certified Installer — one of only a small handful in New Hampshire — and we specialize in the intersection of metal roofing and skylights. If you are worried about winter condensation, dealing with an aging bubble skylight, or planning a re-roof and want to know whether to include skylights in the project, we are happy to walk through it with you.
Call (603) 286-4414 or email us for a free consultation. We serve homeowners across Concord, Tilton, Meredith, Laconia, Manchester, Nashua, and the entire Lakes Region.
F.B.I. Contracting, LLC is a VELUX Certified Installer and full-service metal roofing, skylight, window, gutter, and heated roof system contractor with 22+ years of experience across New Hampshire.
