Why do you get Icicles on your roof?


Icicles can do real damage to your home

Icicles can do real damage to your home

Here’s a winter quickie – icicles are a sign that snow is melting from a hot roof rather than a sunny day.

Since we’ve been talking about DIY energy audits, this is one of the easiest ways of seeing if you’re losing too much energy out your roof. If you’ve got lots of icicles or notice the snow melting unevenly, usually in vertical strips, then you are almost certain to have some major energy loss. Often, this can be fixed quite easily since the icicles and snow melt will tell you where the heat loss is. In fact, this works at least as well as the expensive thermal camera that we use in energy audits. I call it the 30 second energy audit!

This house definitely has problems

This house definitely has problems

So, if this is happening to you, it’s time to climb up to your attic and see what’s happening. Chances are good that you’ll find missing insulation or worse, a bath fan venting into the attic. I’ve even found entire ducts that have become detached! Don’t hesitate, every day, it’s costing you money.

Clear indication of unwanted snow melt.

Clear indication of unwanted snow melt.

And what about those icicles? You know how the road gets torn up with potholes during the winter? Something similar might be happening to your roof. The melted snow can work it’s way into your house and damage it in a variety of ways. It can rip your gutter off, due to increased weight or cause water damage, as the ice melts and drips into areas it wouldn’t have gotten into without the ice. It can even rip your roof sheathing off – as the ice expands, it can exert tons of force, popping nails and leading to serious damage.

One thing you normally should *NOT* do is to install roof heat strips. That’s just wasting more energy to try to fix the symptom of a problem rather than the problem itself. Those heat strips could drive up your electric bills $100+ per month if you don’t watch out. Wouldn’t it be better just to fix the insulation or faulty duct in the attic?

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2 thoughts on “Why do you get Icicles on your roof?

  1. Was looking over the articles on insulating attics and preventing moisture up there, and you have some really great advice!

    Commenting on this article though, because I get ice forming on the roof each winter since I moved in a couple years ago. My unfinished attic has got a very high ceiling – and 2 skylights in it!

    I’m assuming that someone had plans long ago to finish the 3rd floor, but for now, I am feeling like it’s acting like a greenhouse up there, right?

    Do you think I could just cover the windows with plywood or something to block that light? Would that cause other problems in the future?

    • I doubt the skylights are letting much more heat in than the roof itself. Shingles are really effective absorbers of heat and much of that heat goes right through and into the attic.
      If you want to try a simple test, buy a sheet of board-foam, cut it to size, and put it into the openings. A lot easier and much better insulation than the plywood would give you. That way, for a minimal amount of effort, you could see what effect it has on the conditions up there.
      Let me know what you learn. My guess is that, other than blocking the light, it won’t have much effect on the temperature.

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