Ice-melt socks on a metal roof.
January 4, 2016 8:45 AM   Subscribe

We've got a low-pitched copper roof. We had a big problem with ice dams last year and want to try the "ice-melt in pantyhose" thing. But what kind of ice melt?

Basically, the roof is right above the heated interior of the house - no attic or other cold area in between, so preventing the issues that lead to ice dams in the first place is really a non-starter. We've looked into electric heat cables, but the ones we've seen so far are not for use with metal roofs. I've seen some more elaborate (expensive?) systems that integrate into the roof elements, and will look into those in the future.

In the meantime, we'd like to try ice-melt socks this winter, but we want to fill them with stuff that won't corrode or otherwise damage the copper roof. I believe we need to avoid Calcium Chloride for this reason. What about CMA (Calcium Magnesium Acetate)? Is this safe? Anyone have experience with this issue? What products did you use?
posted by Right On Red to Home & Garden (4 answers total)
Best answer: I researched this last year for my own roof and basically gave up at some point.

The gist of information I did find, you can read here:

Calcium Chloride will work at a lower temperature (-25 F) than Sodium Chloride (+20 F). Same with Calcium Magnesium Acetate at +20. Magnesium Chloride's lowest working temp is 0 F.

As for corrosion, here's quote from the linked page:

Like all chloride-based materials, calcium chloride is moderately corrosive to unprotected common metals but, in general, there is little difference in corrosion between the various chloride-based deicers, including rock salt (sodium chloride), magnesium chloride and calcium chloride.

There is of course the consideration of toxicity to vegetation and animals as well for all of these.

What style of house do you live in? I hate to say it but the long term solution is to fix the insulation inadequacy to prevent the ice dams. I'm dealing with it myself in a cape (house not clothing). I've got no insulation on the front half of the roof and up top. The rear has insulation but again the lack of insulation at the top makes it perfect for ice dams to form on the eaves.

PS - Beat the rush and get whatever ice melt you decide on as early as possible along with a roof rake. Home Depot and Lowes were both sold out for me last year.
posted by eatcake at 10:18 AM on January 4, 2016

Those socks are supposed to be laid down vertically (ie. perpendicular to the edge of the roof) and in theory they will create channels for the water to run through. I imagine you need one every 5 or 6 feet to be effective. I second the suggestion that for a real long-term solution you need to fix the roof insulation and ventilation, but if you want to try socks, what I would do is (a) use whatever is said to be the least corrosive, and (b) invest in some heavy-gauge clear plastic (sold in most hardware stores), and put a good wide sheet of this under each sock and extending over the drip edge. This way, very little, or none, of the melting solution will actually come into contact with the roof. Weigh down the corners of the plastic sheets with bricks, stones, or whatever you have. (Or just lay one long sheet of the plastic all the way across, weighed down by the socks.)

The other thing that occurred to me is that if the whole roof is copper, you really should not be getting any seepage through it, anyway. Whether it's standing seam or soldered sheets of copper, all the seams should be watertight. So that might be a remediation avenue to look at, as well.
posted by beagle at 10:58 AM on January 4, 2016

Before going down the sock route, I'd recommend just keeping the buildup of snow off your roof to a minimum using a roof rake. Can you not reach the area in question? I go out with the rake and just pull the reachable snow down.

If not, I have used the pucks that you throw up there in the past and they do work... eventually.
posted by selfnoise at 2:08 PM on January 4, 2016

I have seen calcium chloride in puck form react very colorfully with copper gutters. Created a ton of patina.
posted by release the hardwoods! at 7:04 PM on January 4, 2016

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