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Roofingaka: ice dam formationaka: ice backup

Ice Dam

In Plain English

A ridge of ice that forms at the roof's edge in winter, trapping water that can back up and leak into the building.

Definition

A ridge of ice that forms at the eave of a sloped roof when heat escaping through the roof melts snow, which then refreezes at the cold overhang. The water backed up behind the ice dam can infiltrate under shingles and cause interior damage. Prevention requires adequate attic insulation, consistent ventilation to keep the roof cold, and ice and water shield membrane installation at the eaves.

Why It Matters in Bidding

Estimators bidding roofing or building envelope work in cold climates must price ice and water shield coverage at eaves, valleys, and penetrations, since underestimating membrane footage is a common source of margin erosion. Ignoring attic ventilation and insulation scope can also expose a contractor to callback and warranty claims long after the project is closed out.

Example

Bidding a re-roof on a New England home, the estimator extends ice and water shield three feet up from each eave and adds soffit-to-ridge ventilation to the scope to head off future ice-dam leaks.

Related Terms

EaveVapor BarrierSoffitShingle

Frequently Asked Questions

Most estimators take off eave linear footage and multiply by the membrane width required by code, then add baffles, ridge vents, and supplemental attic insulation as separate line items. Labor for tearing back existing sheathing or correcting ventilation should be quantified separately so the owner can see the prevention scope clearly.
Liability depends on scope and workmanship warranties. If the contract included ventilation and membrane work and it was installed per spec, the manufacturer warranty may apply; if the contractor cut ventilation scope to win the bid, the resulting leaks often fall back on the contractor as a callback expense.
In cold-climate jurisdictions where code mandates eave protection, it belongs in the base bid to keep the proposal responsive. In milder regions it is often offered as a priced alternate so the owner can weigh added cost against winter-leak risk during the award decision.

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