Are they a sign that your home is poorly insulated? I have one area that has some serious icicles–anywhere from 12" to 24". Mixed in among them are smaller ones so I’m a little concerned. I had my roof “supposedly” insulated about 18 month ago and about a year later I needed to have it “topped off” because I couldn’t discern any change and my energy bills went down very little.
So what do you all think? Do I need more insulation or…? TIA for your answers.
Not if they’re on the outside. 
Reported for forum change.
Duckster, you’re right–I posted in the wrong place. I meant to post it on the General Messages forum. Sorry!
If you have a bubble around your house providing climate control, that bubble may need more insulation.
Reported for forum change
You’re lucky it didn’t cut your eye! Those icicles have been known to kill people.
No, don’t put it there! Snarky answers as the first reply are frowned upon there!
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I can fix that.
Moving thread from ATMB to GQ.
You might still have an insulation problem. Hard to say without taking a close look at it.
If your attic is warm and your roof isn’t well insulated, snow on the roof can melt, then re-freeze when it gets to the eaves (since there’s no heat under the eaves), forming ice dams and icicles.
While the icicles aren’t much of a problem (except that they’ll put your eye out, kid!), the ice dams can prevent the melted snow from dripping off of the roof, so some of the water may leak inside your roof and into the home’s interior.
The house I grew up in had heat tape along the eaves. When it snowed, we would turn the heat tape on, and it would melt any ice dams that tried to form there.
As far as ice dam formation is concerned, it’s better to insulate the floor of the attic so that the heat stays in the lower parts of the house. If you let the attic get cold, then less snow will melt to form ice dams and icicles in the first place. Of course, this isn’t always practical, as many homes have the attic converted into a living space that you wouldn’t want to let get cold.
I learned this year that installing gutter covers (expanded wire mesh type) results in icicles. Snow now builds up right to the outer edge of the gutters.
Now the icicles drip onto walkway & patio, creating an ice problem.
I think the poor man’s test for that is whether or not your roof has snow on it a day or so after the snowfall. The snow melts more quickly from houses with poor insulation and less quickly from houses with good insulation (less heat is escaping through the roof), so a snowy roof is what you want.
Icicles form when dripping water freezes. One way that can happen is, as e_c_g said, when poor insulation lets the heat from your house melt the snow on your roof. But normal melting from sunlight and outside temperature can also cause icicles.
If you have really big ones, then that means that lots of water is flowing to that spot. Maybe you have a little dip in your roof there, or maybe two sections join there and form a kind of funnel.
And, of course, fireplace chimneys and vents for the central heat and the hot water heater can cause the roof to be hotter in those specific areas, so ice and snow will melt faster there.
Agree with Greyson Carlisle.
One question for the OP - is the spot where the icicles are forming on a south-facing roof? If so, it might just be from the cycle of sun during the day, freezing at nights. But if it’s a north-facing roof, and the temperature’s been well below freezing during the day, more likely that the icicles have been forming because of escaping heat from the house.
Icicles can also be problematic in that the weight can damage your gutters.
And you can also get some idea of the cause by comparing your house to your neighbors’.
Of course roof material & direction / angle to the sun can play a big part it in. The back of my roof always melts faster than the front but that’s due to solar heating.
In some places, the cops look out for snow-less roofs and send the sniffer dogs round to check for attic conservatories.
How do sniffer dogs get to the attic? Are they training them to use ladders now or are they strapped to drones?
Now you’re being silly… They lower them from the helicopter in a harness of course.
Not likely. If the sun can melt the ice, then the temperature must be near freezing (at least 28f (-3C) or so). That’s not cold enough to re-freeze the water in the minute or so that it takes the water to reach the edge of the overhang.
There is a 99% chance that the cause of icicles is heat loss from your house to the roof. In other words, poor insulation in that spot.
Water moves very slowly over (or under or through) snow, causing a drip, drip, drip throughout the day. At night, the droplets on the eaves freeze because the eaves are already colder than the roof because there’s cold air from all directions at the eaves. More drips follow, forming an icicle. Repeat with more melting the next day and more re-freezing the next night.
Not to say that all houses don’t have some degree of heat loss through the roof, but even in well-insulated houses, you can spend all day listening that that infernal dripping, then wake up the next morning to an impressive display of icicles.
If there’s a 99% claim to be made for icicle formation, I’d apply it to gutter issues rather than with roof insulation.
So the icicles on my unheated sheds are caused by some invisible heat generation device that I know nothing about? The roof over the attic is heated differently than the part over the eaves. My raingutters back up onto the roof every winter with ice. The insulation in my attic is on the floor. Nothing is against the roof.