Preventing ice dams with ventilation

Insulation · Venting Roofs · printed page 240 (PDF page 241)

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Book index entries

Preventing with Ventilation Helps Prevent Ice Dams Ventilation – Prevents Ice Dams Ventilation Venting Roofs

Text in the illustration

no ventilation
ventilated
cold roof
warm roof
25°F
snow melts and runs down roof
trapped water
ice dam
45°F
insulation
escaping heat
backed-up water gets into house
no soffit vent
wall
75°F
ridge vent
snow on roof doesn't melt
air flow
30°F
upgrade insulation if necessary
keep air path open
continuous soffit vent
gutter not shown
cross section
note:
ridge venting is more effective than individual upper level vents

Generated explanation

Two roof-and-wall cross sections compare an unventilated attic with a soffit-to-ridge ventilated attic under snow-covered roofs. In the unventilated example, escaping indoor heat warms the attic to 45°F, causing snow to melt and run toward the cold eave, where an ice dam traps water that backs up into the house. The ventilated example shows outside air entering a continuous soffit vent, passing through an open air path above the eave insulation, and exiting a ridge vent. Its attic is labeled 30°F with 25°F outdoors and 75°F indoors, and the roof snow remains unmelted. Checkmarked annotations recommend a ridge vent, continuous soffit ventilation, an unobstructed air path, and insulation upgrades if necessary.

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