Monday, February 22, 2010

Apple #441: Icicles

This past week, there were tons of icicles hanging off my house.  I took a lot of pictures of them.

Looking out the east window:

The west side of the house, from the street:

When I was a kid, I thought icicles were really cool and also romantic-looking.  They didn't seem to show up very often, and I don't think we ever had them on our house.  When I saw them on other houses, I was jealous.  I thought they looked old-fashioned and I took them to be a sign that whoever lived in that house with icicles was enduring a true winter, the way winter was supposed to be.

But then at some point my parents told me that icicles were bad.  If you were a homeowner, you would not want icicles hanging off your roof because it meant all sorts of bad things about your roof and your eaves and so on.

It seemed that other people knew this, too, because I didn't see them as often anymore.  It seemed that other homeowners knew that icicles were bad and had taken steps to ensure they wouldn't form on anything.

This year, the precipitation and the temperatures must have been just right because there were icicles everywhere.  I'm talking huge ones.  Really long dagger-like ones, and also curtains of them all along the sides of houses.  Not just on my house, but throughout my neighborhood and, apparently, all over the city.

These icicles are on the north side of this house.
(Photo by the Apple Lady)

  • Icicles form when the temperature is right about at freezing, but the sun is shining.  The sun melts the snow on a roof and as the melted snow drips down, the air temperature freezes it again.
  • When that droplet of water freezes, it releases a tiny amount of heat.  That little bit of heat travels up to the top of the icicle.  
  • As the heat goes upward, it diffuses away from the icicle. So there's kind of a triangular updraft going up and away from the icicle.
  • This allows more snow and ice to melt at the top and to continue to travel down the length of the icicle, where it tries to drip off the end but because of the colder air temperature, freezes there. 

I'm not sure how well you can see them, but there are drops of water at the end of each of these icicles.
(Photo by the Apple Lady)

    • Icicles often get ripples in the middle of them because of the warring forces of gravity and surface tension.  Gravity is trying to pull the droplets of water down, while the surface tension inherent in water means it's being pulled sideways toward the surface of the icicle. 

    Icicles with ripples
    (Photo by the Apple Lady)

      • The way our homes are heated also contributes to the formation of icicles.  Heat that escapes through a poorly insulated roof will make the snow on the roof melt faster.  When the melting snow hits the uninsulated eaves, icicles will form there.
      • Icicles can be dangerous when they break off and fall.  My mom was once hit in the head by a falling icicle and she had to go to the emergency room.  They gave her, not stitches, but staples in her scalp. It was not fun.  You really don't want to get hit in the head with an icicle.
      • In addition to the safety aspect, icicles can signal potential problems with roof leakage.  When ice and snow build up at the edge of a roof, they form what's called an ice dam.  Basically, an ice dam concentrates a lot of moisture that keeps melting and re-freezing in one spot on the roof and after a while, the roof can't handle all that moisture and it gives up, and in comes the water.  You do not want this to happen, especially since a lot of basic homeowner's insurance policies don't protect against damage due to ice dams.

      You can see how the snow has melted on most of the roof but collected at the edge. The icicles have formed from the snow dripping off the eave.
      (Photo by the Apple Lady)

        • To prevent this sort of badness happening to your roof, make sure your home's attic and the spaces under your roof are properly insulated.  This will keep the snow from melting as quickly and forming icicles or ice dams.
        • Most building codes also require that a roof be properly ventilated.  Roof ventilation will keep warmer air flowing around the eaves in the winter time and in the summer, will allow warm air and moisture to escape and keep the roof from getting too hot. Usually this means there have to be vents under the roof's overhang (soffit vents).
        • A lot of the houses and buildings in my neighborhood are really old and the roofs were probably built before housing codes required ventilation and certain amounts of insulation.

        This older gray house looks sad with its big icicle hanging off the dormer roof.
        (Photo by the Apple Lady)

        • Another thing that can happen is that downspouts get clogged with debris and then the water trying to get out of it freezes, and the whole thing backs up into a kind of frozen fountain.

        The water trying to get down this downspout (above) apparently couldn't and forced its way out from the top and gushed down alongside the downspout. Looks like a similar thing happened to the next one, too. (Photos by the Apple Lady)

        On my roof, the gutters hang a little way from the edge of the roof. I don't know if they were built like that many moons ago, or if, over time, they have gotten pulled away from the edge. Regardless, the water spills out over the edge of the gutter and drips off both sides and forms a curtain of icicles.
        (Photo by the Apple Lady)

          • Some people go out and knock the icicles off their roofs with a long-handled broom or other such implement.  But roofing people say don't do this.  If you knock a big fat, heavy icicle off the roof, chances are it might still be frozen to part of your roof and you could wind up ripping off a hunk of eaves trough or shingles or some other crucial part of your roof along with the ice.  
          • So then you'd have to get your roof repaired, but a roofer isn't going to go up there while it's all covered with ice and snow.  Roofers have to wait until all that stuff melts before they to do the repair, and that melting snow would then probably leak through your now-broken roof into your house.  
          • The moral is, let the icicles melt and break off on their own.  Then when it's warmer, get your roof insulated properly and solve the problem at its source.

          These icicles are so long and yet so close to the ground, it would be very tempting to snap them off. But because of all that ice that has formed at the top of the icicles, you'd risk ripping off part of the eave or roof.
          (Photo by the Apple Lady)

            • Or if you're a renter like me and can do nothing about the situation, enjoy the icicle show and take a lot of pictures.

            I took these photos with my camera on various night settings and then adjusted the levels in Photoshop so you could see the icicles.  When I did that, all sorts of other colors showed up.



              (Photos by the Apple Lady)

    , Ice Melting: How Icicles Form
              Mahalo Answers, "Why do icicles form on the gutters of a house and what can be done to prevent them from forming?" January 18, 2009
              "Why Icicles are Long and Thin," Science Daily, February 1, 2007
              "The Point of Icicles," Science Daily, October 4, 2006
              Keith C. Heidorn, Weather Phenomenon and Elements, Icicles
              Anya Sostek, "Western Pa. growing bumper crop of icicles," Pittsburgh Post-Gazette, January 12, 2010
              DOE, Ceilings and Attics: Install Insulation and Provide Ventilation


              1. Those actually look very dangerous! Be careful walking underneath them; we'd miss your posts.

              2. Aw, thanks for the concern, Pam. But these icicles hang over a porch roof, so there were no worries. I listened to them go crashing off the eaves onto porch roof most of the next day.

              3. When I bought my house, I didn't know anything about ice dams, and I would see my neighbors out after a snow storm with this long scraper thing, and they'd be scrapping the snow off their roof. I thought it was silly at first, until I noticed I had huge ice dams and they didn't! Now I need to find out what that scraper is!


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