What are Ice Dams?
- Forms when heat from house escapes into the attic and warms the roof, which melts the snow.
- Hot Air Rises, the upper areas of roof become warmer than the eave area.
- Snow on the upper roof melts and refreezes at the eaves and lower valleys
- As the freeze thaw cycle recurs (night & day) a ridge of Ice develops and traps water on the roof.
- As the roof/attic area warms it will cause the ice to melt
- That melted snow & ice will then enter the home at a point within a vertical plane 24” -36” inside the inside wall of the structure
- Moderate to Heavy Snow is frequently followed in daytime with temperatures of 15 to 25 degrees.
- Add a little light rain and you have ignition!!
On the other hand…
As folks in Maine, NH & Vermont know
- Really cold temperatures will forestall the freeze – thaw.
- Why – because most homes will have sufficient insulation on floor of attic to keep interior heat from overwhelming the outside temps at top of roof.
- If the outside temperatures gets to the upper 30-40’s the temperatures will be too high to support eave freezing
- A Delicate Balance – eh??
What to do??
- Keep the underside of the deck cold.
Keeping Roof Deck Cold
- Ridge to Soffit Ventilation
- Add Roof insulation with Ventilation
- Atlas Cross Vent – 4 way ventilation-
- Spray Foam under Roof Deck /Gable Ends & Eliminate attic Vents
Fact Or Fiction?
- No correlation between Gutters & Ice Dams– However, Ice weighs 45-60lbs Cubic Foot
- Ice & Water Shield Prevents Ice Backup– Prevents the effect-if installed so that “belt” extends
to a point even with 24-36” inside wall plane
- Heat Cables Prevent Ice Dams– Just causes another one above & inside it
- Panty Hose & Salt– Causes roofing & flashing deterioration-plant damage