An ice dam forms when heat from the house warms the roof deck enough to melt snow higher on the slope. The water runs down until it reaches the colder overhang, where it freezes. Over several days the ridge of ice grows, and new meltwater pools behind it. Shingles are designed to shed water running down, not water sitting against them, so the pooled water works its way under the shingles and through nail holes.
In Highlands Ranch the pattern tends to show up on the shaded sides of two-story houses, at valleys where two roof planes meet, and above rooms with vaulted ceilings, where insulation depth is limited and warm air collects near the roof. Strong winter sun often clears the south slopes within a day or two while the north side stays frozen.
Signs an ice dam is leaking
- Thick ice along the eaves, often with icicles hanging from the gutter
- Stains at the top of an exterior wall or along the window head
- Paint bubbling or drywall tape loosening near the ceiling line
- Drips at a window or patio door after a sunny afternoon
- Wet insulation or frost on nails in the attic above the eave
- Water in a basement corner directly below a frozen gutter downspout
Ice dam leak or plumbing leak?
Both can stain the same ceiling. The timing usually separates them.
Points toward an ice dam
- Stain appears after snow followed by sunny days
- Stain is along an exterior wall, at the ceiling edge
- Dripping stops on cold nights and returns in the afternoon
- No plumbing fixtures are above the stain
Points toward plumbing
- Stain grows regardless of weather
- There is a bathroom, laundry or kitchen line above it
- The water meter keeps moving with everything turned off
- Stain is in the middle of the ceiling, away from exterior walls
After the leak
- Catch and document.Put containers under drips, photograph the ice on the roof and the damage inside, and note the dates of the snow.
- Check the attic.If you can safely reach it, look for wet insulation above the stained area; compressed wet insulation loses much of its value.
- Open the wall if needed.Exterior walls behind a stain may have wet insulation and sheathing. Moisture readings decide whether the drywall needs to come off.
- Fix the cause in spring.Air sealing, attic insulation, ventilation and roofing details are the long-term answers; a roofer and an insulation contractor can assess each.
Common questions
- Do heat cables solve ice dams?
- Heat cables can keep a channel open at problem spots, but they treat the symptom. Reducing heat loss into the attic is usually the more durable fix. Ask a roofer which approach suits your roof.
General information for Highlands Ranch, not a quote or professional advice. In an emergency, call 911.