For clarification, a drip edge is a modified L-shaped flashing used along the eaves and rakes of a roof. The drip edge directs runoff water into the gutters and away from the fascia. In terms of placement, the drip edge should be installed under the roofing felt on the bottom edge of the roof and over the roofing felt on the gable ends, if applicable. The drip edge is supposed to be placed with a ¼-inch gap between the flashing and the edge of the roof sheathing or fascia. This gives a drip line that is not butted directly against wood trim.
It is unlikely that mis-installed drip edges will have a significant effect on the occurrence of ice damming. However, it can increase the water getting into the wall/eave area from ice damming or other causes. It could also lead to accelerated rot at the eaves/fascia area.
Ice dams are a cold weather problem caused by snow melting over heated portions of a building and refreezing at colder portions of the roof, creating a dam. Water produced by subsequent melting then backs up under the shingles, eventually causing damage to insulation, interior finishes, and more. The snow melts due to heat loss into the attic from inadequate insulation, air leakage, and/or inadequate ventilation.
Ice dam precautions include:
- Making sure the roof is adequately insulated to account for local climatic conditions.
- Installing raised-heel trusses, if necessary, to allow full-depth insulation and proper ventilation over exterior walls.
- Sealing all penetrations into the attic from ceilings or walls.
- Installing continuous soffit-and-ridge vent systems and baffles at the lower side of the roof, with a clear pathway of at least two inches between the top of the insulation and the roof sheathing.
You may also consider insulating around and sealing leaks from ducts and vents in the attic, although the primary emphasis should be on providing proper ventilation and following good insulation practices.