Rooftop ice dams are a common problem during late winter and early spring.

They form when snow melts and then refreezes in eaves troughs and on rooftops.

"The overhang of your home is frozen because it has no interior insulation or heat rising up through it. So it stays as a block of ice when the water runs down, hits this block of ice and creates the infamous ice dams," said Ken Gascoigne of Empire Roofing.

Gascoigne said the problem is more common in older homes.

"The real secret is too keep this attic space cold and well-vented... adding roof vents helps and adding insulation helps," Gascoigne said.

Experts say homeowners can - and should - use a roof rake to remove snow from the first metre of the roof.

That's what Munir Bishouty did all winter.

"The weight was heavy on the roof. The ice was a lot and we may have a larger problem when it thaws," he said.

If ice dams do form, removal could cost $300-$400.

Lamontagne, a sales associate at Tamar Building Products, said ice dams block water from draining off the roof.

"The water would come in up underneath the shingle, soak the installation, then you could get mold and mildew in the attic space," he said. "You could also get dry rots in your framework of your home. It could soak into your drywall creating water stains and it could also damage paint."

Lamontagne said the worst thing a home owner can do is throw salt on the roof.

"That will actually eat away at the shingles and create much worse problems further down the road," he said.

Ice Dams

A look at how ice dams form. (Courtesy Emplire Roofing)