Snow melting on the roof: normal, or a warning?
Where the snow melts, and where it does not, tells you how the roof is losing heat.
Snow melting on the roof is not a problem by itself. Sun does it, and so does a warm afternoon. The warning sign is snow that melts in patches while the rest of the roof stays white, or melts at night when the air is well below freezing. That pattern means heat is coming up from inside the house.
Two reasons snow melts
The first is weather. Sun and warmer air melt snow evenly, usually from the sunniest side first. The roof loses its snow in a fairly even way and the meltwater drains without trouble.
The second is heat from below. Warm air leaks through gaps around lights, hatches, wiring and chimney chases, and warms the underside of the roof deck. Snow above those spots melts first. The roof then looks patchy, with bare stripes or squares that follow the layout of the rooms below.
What to look for from the ground
Stand back, and use binoculars if you have them. Do not go up to check.
- Bare patches on a cold day, with snow all around them.
- A roof that is clear near the ridge but heavy with snow at the eaves.
- Steam or a damp look on the shingles on a very cold morning.
- Icicles forming along the eave under the melting areas.
Any of these suggests the attic is warmer than it should be. A good attic stays close to the outdoor temperature, and the snow on top sits there until the weather changes.
Why it matters
Meltwater has to go somewhere. It runs down to the eave, where the deck is cold and the water freezes again. Layer by layer that becomes a ridge of ice, and behind it the water can back up under the shingles. We explain how that chain works in what causes ice dams, and what the leak looks like in ice dam leak.
So the answer to the question depends on timing. Melt on a sunny, mild day is fine. Melt on a bitter night, or in bare patches, is worth acting on before the next big snow.
What to do about it
You cannot fix this from the roof, and you should not shovel or scrape shingles. Treat the attic instead. Seal the air leaks from the rooms below, even out the insulation and keep the soffit vents clear so cold air runs under the deck. Preventing ice dams lists the steps in order.
A roof rake used from the ground can clear the lowest stretch of snow after a heavy fall. It is a short-term measure and does not replace the attic work.
When to bring in help
An insulation or weatherization contractor can find the air leaks, often with a blower door test. Call a roofer if shingles look lifted or damaged, and a licensed structural engineer if the roof line looks bowed under the snow.
Frequently asked questions
Why is snow melting on my roof when it is freezing outside?
Heat from the house is usually warming the roof deck from below, through air leaks and thin insulation. The snow melts from underneath even though the air is cold.
Is snow melting on a roof normal?
On a sunny or mild day, yes. Melting in bare patches or at night in hard freezing weather is a sign of heat loss.
Does melting snow cause ice dams?
Uneven melting is what feeds them. The water runs to the cold eave and refreezes there, building a ridge of ice.
Should I remove snow from the roof?
Not by climbing up. From the ground, a roof rake can clear the lowest stretch after a heavy snowfall, but the lasting fix is in the attic.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- NOAA / National Weather Service. Winter — National Weather Service safety hub
- NOAA / National Weather Service. What To Do If You're Caught in a Winter Storm