The attic needs ventilation. If the blizzard covered the roof vents - heat will build up in the attic. You need someone to go up on the roof and clear the snow from the vents.

Ice dams are often caused when snow melts on the roof surface and refreezes over the eaves---where the roof is colder.

The best treatment is to install heated strips to melt the ice at the freezing points.

Both answers are good ones, insulation alone won't alleviate ice dams. They may have blocked off the soffit vents with insulation which happens often. That is if there is soffit venting. Before calling out the insulators you must check that the soffits vents aren't plugged with insulation. There is also a product for the eave area called ice socks they seem to work well.

I have to disagree with the idea of heating cables. A properly insulated and vented attic needs no heating cables.

" A properly insulated and vented attic needs no heating cables."

Until the sun causes melting with a large eve overhang.

" A properly insulated and vented attic needs no heating cables."
Agreed

"Until the sun causes melting with a large eve overhang."
It's only an ice "dam" if it prevents the melt/runoff from getting off the roof. It's irrelevant if there is ice formation at the leading edge. The ice dam only poses a problem if it causes a back-up that finds it's way into the house. If the sun is causing the melting then it should melt from the top down and the run off should be able to get off the roof. A properly insulated house should not allow heated air insode the large eve overhang and there should be soffit vents on the underside of the overhang to keep it the same temperature as the outside clod air which should keep the bottom frozen and promote the natural "top-down" melting from the sun.

Actually the sun is good. The problem is the 28 - 32 degree, cloudy day,

The sun on a very cold day will produce ice dams in many cases.

As soon as the melt water hits the eaves where there is NO heat leakage it freezes up.

It is not at the edge of the roof, but right at the start of the eaves.

Insulation is NOT a 100% thing, nor is ventilation.

Insulation slows heat movement, but does not stop ALL heat movement.

Ventilation needs at least some heat leakage to cause air movement.

The surest weay is to put in a roof edge that extends well past the start of the eaves that stops ALL water penetration.

Sheet metal used to be common for the edges of the eaves.

A decent width of ice and water shield under shingles is also effective.

The barrier must extend further up the roof than the exterior walls under the roof.

A 'cold roof' (actually two roofs with a space between them) is another even more expensive solution.

FWIW: The Grace Ice and Water Shield high snow area detail shows a strip of ice and water shield membrane wrapping past the edge of the roof and onto the vertical fascia board. The upper leading edge of the this strip is then stripped in again to tie to the i &w s membrane on the roof.

The memberane should extend a minimum of 6 ft beyond the plane of the wall below the soffit. So for example, if it's 3 ft from the edge of the roof to the wall, then you should put at least 9 ft of ice and water shield on the roof.

I have a realtively low pitched roof here in MA on my modest raised ranch-style house. I had a terrble ice dam problem especially at the bow window where the trim at the head of the window continued vertically up into the soffit making this "heated" space under the roof. When I re-roofed I had the contractor cover the enitre roof with ice and water shield.. I have not had any leakage since.

Sometimes ice will form and there is likely a dam, but as long as the water stays out of the interior spaces. It doesn't bother me.

Wow thanks for the responses! My computer is in the shop and I'm on a borrowed iPad at the moment.

I have to admit that I'm now even more confused and will have to study your replies some more. My roofer was a jerk and I have no idea if I have water shielding or not. On another forum it was suggested that I may have a lot of air leakage in the attic. I am unable to get into the attic as it's one of those stupid ceiling trap doors that's requires a tall ladder. I'm slightly disabled and if I got up I'd never get back down.

I have no idea if water is coming in, but I have seen no leaks in the house. The eves are very short and the new gutters are right under them. I'm trying to fix up this house and having a hell of a time with contractors. So far only my furnace company has done a professional job. Sigh.

Thanks for,the feedback. I appreciate it. :)

You probably don't have the shield if you don't remember paying for it, it's expensive.

The heating strips are a good backup if your area is prone to damming. Mine supposedly isn't, but it's been a bad year for ice damming. I'm planning to put heat strips in for these situations...you don't have to run them all the time.

My roof needs more insulation, but I've got recessed lighting etc I want to put in, so want to delay doing it until it's finished.

Ventilation's important too.

yo may not have to run heat strips all the time, but you do need to be there to run them on while it's snowing. to keep all the snow from accummulating Once the dam forms you just melt holes where the tape is but the rest is there for a while until it melts.

I've been reading this thread since its first post.
Now, I have no cold climate experience, but just
felt like I needed to put this out there.

If insulation was added over air leakage sites
then the insulation has little R-value with air moving through it.

things like bath fans that are not sealed well
around housing penetration into living space
allow a lot of warm, moist air into attic.
stove vents, recessed lights & attic accesses
are large air leaks.

if ducts are in the attic..then you have hot
air escaping from duct leakage.

as these items are sometimes located close
to eaves of the house, it makes sense that
snow would melt, run to lower point & re-freeze.

like I said, not cold climate expert. hot humid is my
climate.

insulating without air sealing is wasteful.

was any air sealing done prior to insulation install OP?

best of luck.

" you do need to be there to run them on while it's snowing"

Or just use a thermostat to control them.

http://www.energyvanguard.com/blog-building-science-HERS-BPI/bid/58341/ice-dam-bandaid-solution-heat-strips-on-the-roof?source=Blog_Email_[Ice%20Dam%20Bandaid%20Solu]

sorry for the cut & paste link, but this is an article from a
building science perspective that explains what I tried to
interject into this conversation.
even with ice shield underlayment, if there is air escaping into the attic from the living space... heat strips are an expensive way to cover a year round problem.

fyi OP, it may not be the roof..but the leaks in the
air barrier at the ceiling into the attic, or duct leaks
if ducts are in attic. look to solve the issue, not
bandaid the problem.

best of luck.