Usually condensation. Warm, moist air inside the building reaches the cold steel or the cold roof deck, condenses or freezes, and drips or melts on the next sunny day. Drips that come only during rain point to a leak instead.
Get My Free Estimate →Water dripping under a metal roof on a cold, dry morning is usually condensation, not a leak. Steel loses heat fast on clear winter nights, and when warm, moist air touches the cold metal, the moisture turns to water or frost on the underside.
How you stop it depends on what sits under the panels. Buckshot installs and repairs metal roofs in Madison from our office on North Sherman Avenue, and this guide covers homes, garages and pole barns.
Why metal roofs sweat in winter
Air holds water vapor, and when it touches a surface colder than its dew point, the vapor condenses on that surface. On a clear winter night, a metal roof radiates heat to the open sky and can cool below the temperature of the air around it.
Below freezing, the moisture builds up as frost on the underside of the panels. On the first sunny morning the steel warms, the frost melts at once, and it can look as if the roof is leaking everywhere.
The more moisture inside the building, the worse it gets. Showers, cooking, unvented propane or kerosene heaters, wet cars carrying snow into a garage and livestock all add water to the air.
Condensation or a roof leak?
Timing is the best clue. Condensation follows cold, clear weather, while a leak follows rain or snowmelt.
| What you notice | Likely cause |
|---|---|
| Drips on cold, clear mornings or the first sunny day after a cold snap, with no rain | Condensation |
| Damp or frosty spots spread across the whole underside of the panels | Condensation |
| Drips in the same spot every time it rains | A leak at a fastener, seam or flashing |
| Drips along rows of exposed screws during rain | Loose screws or worn washers |
| Water near a wall or chimney during rain or a thaw | Failed flashing |
Our guide to roof leaks when snow melts covers melt leaks. Snow lying on the attic insulation is a third problem, covered in our guide to snow blowing into the attic.
Metal roofs on homes
On a house, residential metal roofs go over solid decking with synthetic underlayment, and ice and water shield at the eaves and valleys. The underside of the panels never meets the air in the attic, so the steel itself is rarely where the dripping starts.
When a house with a metal roof drips in winter, the moisture usually comes from the house. Warm, humid air leaks into the attic through the hatch, light fixtures and bath fans, then freezes on the cold roof deck the same way it does under shingles.
The fix is the same as for any attic. Bath fans have to vent outside, the attic floor needs air sealing, and intake and exhaust vents have to be balanced, as our guides to frost in the attic and bath fans venting into the attic explain.
Exhaust vents go in with every new Buckshot roof, and our attic ventilation work balances them with soffit intake so the deck under the panels stays dry.
Garages, shops and pole barns
Condensation is worst where metal is screwed straight to purlins or trusses with nothing underneath. There the bare steel is the ceiling, and all the moist air in the building reaches it.
Heated shops, garages where wet cars park and barns with animals drip the most. A building that stays dry all fall can start dripping once the heater runs and the nights turn clear and cold.
The proven fix for open framing is a barrier under the steel. Panels can come with a factory-applied drip-stop membrane that holds condensation until it dries, or a condensation-control liner can go under the panels when the roof is installed.
Ridge and eave ventilation then carries moist air out before it reaches the roof. Our agricultural and pole barn roofing crews install and re-roof metal on barns, sheds and outbuildings, and our guide to standing seam vs corrugated metal compares the panel types.
Cutting the moisture at the source
Less moisture means less condensation under any roof. These steps help in every building with a metal roof.
- Vent bath and kitchen fans and clothes dryers outside, never into the attic or the building.
- Use a vented heater in a shop or garage, because unvented propane and kerosene heaters add water to the air as they burn.
- Let snow melt off cars and equipment where the water can drain away, and squeegee standing water out.
- Keep indoor humidity moderate in deep cold, and run exhaust fans long enough to clear steam.
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What condensation does if it is left alone
Repeated wetting rusts screws, washers and the underside of the panels, and wet insulation loses much of its insulating value. On wood purlins and roof decks it leads to rot, and in a home it shows up as ceiling stains and mold on the sheathing.
In barns and shops, the drips land on hay, feed, tools and vehicles.
Water dripping under your metal roof? Our inspection is free, and we will tell you whether it is condensation or a leak before anything is quoted. Call (608) 909-9109 to schedule it.
Free on-site inspection · Family-owned since 1979How metal roof condensation is fixed
- Confirm the cause. The roof is checked for loose fasteners, worn washers and failed flashing, and the drip pattern is matched to the weather, so a leak is not mistaken for condensation.
- Cut the moisture. Fans, dryers and heaters are vented outside, and air leaks from the house into the attic are sealed.
- Balance the ventilation. Eave or soffit intake is opened or added and paired with ridge exhaust, so moist air leaves before it reaches the cold steel.
- Add a barrier on open framing. On a re-roof or a new building, drip-stop panels or a condensation-control liner go under the steel.
- Repair the damage. Rusted fasteners are replaced, wet or rotted decking and purlins are repaired, and any leaks found along the way are sealed.
Our Madison crews also handle fastener, flashing and panel repairs on existing metal roofs when the problem turns out to be a leak.
Madison winters and metal roofs
Madison averages about 52 inches of snow a year, according to the Wisconsin State Climatology Office, and the coldest nights tend to come with clear skies. Condensation problems usually show up in that coldest stretch of winter.
Metal itself is a strong roof for Madison. It sheds snow, stands up to wind and can outlast two or three asphalt roofs, as our comparison of metal and asphalt in Wisconsin winters explains.
Get your metal roof checked
Buckshot Exteriors is family-owned, has served homeowners since 1979, and is headquartered on North Sherman Avenue in Madison. Our own crews install and repair metal roofs on homes, garages and farm buildings across Madison and Dane County.
Call (608) 909-9109 to schedule a free metal roof inspection, or send us a message and we will set a time. If you would rather check first, note whether the drips come on clear, cold mornings or during rain, because that one detail points to the cause.
Get a straight answer on your Madison roof
Wisconsin storm season and insurance non-renewal letters do not wait. Get a free, no-obligation inspection and an honest assessment of exactly what your roof needs, even if the answer is to wait.