Ice dams

I think I understand the mechanics of ice dams. Up until recentely they were just an academic topic for me. I now own a home that is suglect to occasional ice dams. Two occurances in the last 5 winters.
The roof is metal (standing seam?), dams (so far) have only occured in two places on the ~south facing roof slopes.
Question............is this a design problem, construction problem or so they just happen?
Is the solution something like Raychem heating cable?
Bob
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a better insulated roof/attic is less prone to ice damn formation,

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On 06 Jan 2005 04:09:23 GMT, snipped-for-privacy@aol.com (Bob K 207) wrote:

Only being the south side implies you have good insulation, it might be the sun over warming the upper parts of the roof sending down melted snow.

Not an expert here, but I wonder why it's blocking up at the bottom, do you have a blocked up(dirty) gutter?

I think that is something you should think about over the summer since gettin up on a wet/icy building could be unsafe.
Try this. Get some of the safest ice melt out there( I think it's magnesium cloride), fill a sock with it, and tie it to a rope. Toss it up to the roof. pull it down so it's right above the ice dam. The ice will melt around the sock giving a path for the water and other melting ice a path to the gutter. Might even unblock your potentially frozen gutters.

Now that's what I would do...
Tom @ www.ChopURL.com
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On 06 Jan 2005 04:09:23 GMT, snipped-for-privacy@aol.com (Bob K 207) wrote:

Ice dams are caused when snow on the roof melts and then refreezes several times over.
There are many things that can cause them.
I refer to the roof over an attic, but same factors apply to cathedral ceiling and other areas where there no attic, although the cures may be different.
Inadequate attic insulation allows heat from the house to warm the roof, melting the bottom layer of snow, which then refreezes when it gets colder (usually overnight).
Inadequate attic ventilation can cause or contribute to the problem by not removing any warm air that does make it to the attic. Ideal is to have both soffit vents and ridge vents so a steady flow of cool air flows under the roof deck, keeping it very cold so snow doesn't melt. Sometimes otherwise adequate ventilation is blocked in some areas by skylights, poor framing, misplaced insulation, etc.
Local heat sources, such as light fixtures, especially older ceiling can lights that were not well sealed, can generate local warm zones that cause ice dams.
Air leaks from heated space into the attic or roof area can also cause local heating and melting. Again, light fixtures, wiring and plumbing penetrations, and bath fans are common areas for air leaks. Likewise bath fans that are vented into the attic rather than through to the outside dump both warm air and moisture right where you don't want it.
Finally, under some weather conditions it is almost impossible to prevent ice dams. If the roof warms up above freezing during the day (maybe in sunny areas) and then drops below freezing at night, you are going to get some ice formation. Periods of sleet or freezing rain also can lead to dams. That's why current best practice (and most codes) require ice and water membrane near the edges of the roof under the shingles (metal roof in your case) so that even when dams occur, the water doesn't work through the roof and cause damage.
Heat cables can prevent the problem by preventing any buildup of snow in the first place, but they are really a poor substitute for fixing the actual problem. And they can be quite expensive to operate. They are really only effective if you have them turned on before it starts snowing...they don't generate enough heat to melt big loads of ice and snow after the fact.
HTH,
Paul Franklin
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... al lot of good stuff other than...

I beg to differ with where that last statement is going. Heat cables are NOT intended to melt your roof clean, even if they are up before the storm. What they do is prevent a total dam build up by keeping open drainage channels.
I had some success with putting heat cables up "after the fact over the past fiew years.. It was a truely miserable experience, (well I did it several times, and got it down to an art) but once they were up, they melted channels in the ice, and drained out any subsequent backup.
Once installed, you should only power them when you need them. You can get temperature sensitive controllers too.
Dave.
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wrote:

Thanks for the info,Dave. I'll put up the cables in the spring for next winter. Last winter the south side of the house had thick ice dam across the whole length of the roof. The ice was even over the edge of the gutters. I went to the hardware store and bought a hose attachment for the kitchen faucet. I hooked up garden hose and spent the day spraying water on the ice to create channels & dragging the hose back inside and back out again.
It was a pain, but I had success with the project. I don't think this will work if anyone has a 2 story house cuz the water cooled off really fast. I must have gone thru 20 tanks of hot water doing it. Marina
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the cables in the spring for next

will
marina and others: next time go to your local rental store and rent a steamer. This is a device that you hook a hose into and it pumps out hot water. Looks kind of like a pressure washer, but puts out hot water instead of pressurized water. This is the tool for dealing with ice dams.
Cam
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Ice dams occur when heat rises th rough the roof. This melts the bottom of the snow. The water runs off the roof, and then refreezes when it reaches th e (unheated) eave.
The solution is more insulaltion under the roof, and also ventilation between the roof and the insullation.
Icicles mean that you are losing heat through the roof. My parents house had this problem for many years. I remember my Dad up on a ladder with an ice pick many years. Blown cellulose, and a couple of eaves vents solved the problem.
--

Christopher A. Young
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On Thu, 06 Jan 2005 15:00:22 GMT, "Stormin Mormon"

Ice dams can be completely unavoidable. Try living in a community where the sun shines a lot. Where temperatures in the sun almost always go above freezing but in the shade almost never. It can get right ugly on the north and north west side of buildings.
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wrote:

Right, we have venting and everything good. Still get ice dams sometimes. Along the south side it was terrible. Also in the valleys it was bad. Pasar
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There's been several good notes on ice damming causes and solutions so far. I'll just relate my experience which will probably just reiterate points already made.
My roof problems occured in three places:
In cathedral cieling above recessed light fixtures
At junction between two sections of my house - one being the cathedral cieling section, the other being an attic type roof (truss).
Near same junction where furnace chimney comes out.
Solutions:
Placed roof vents directly over recessed lights. Surprisingly cheap and easy, totally effective in eliminating melting at those spots.
Add ridge vent to attic-roof portion of house. Made this a truely "cold roof" without any melting except around chimney.
This has solved my problems completely, for over 5 years now. I still get melting around the chimney, but it doesn't cause damming problems, yet. If it does.... The roofing guy told me (as others have said) that there are certain places and/or times that melting is just impossible to prevent. Nowadays, well designed houses of course try to eliminate these areas, but they can also use a material to provide a waterproof layer between the roofing and the sub-roofing. Can't remember what it's called. Of course, retrofitting would be a "project" on my house (asphalt shingles), but I'll do it if needed and/or when I need to re-roof. We did a small section this way at our previous house and it was not a huge deal with a metal roof (which you can remove without destroying it).
Good luck
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