Ever since I was a teenager working at a hardware store, I've heard of people filling up pantyhose with salt and tossing them on their roof to create drainage channels in ice dams. After hearing about this so many times and even seeing this method of creating drainage channels in ice dams on the news, I began to believe this actually worked.
Nevertheless, I tend to question everything, and last year I finally got around to testing this method on my own. Instead of laying the pantyhose perpendicular to the ice dam, I laid them parallel to the ice dam in an attempt to get rid of the ice dam entirely. As I mentioned in my blog about how to remove ice dams, this didn't work well at all.
Several readers suggested I place the pantyhose the way everyone else does (does everyone else really do this?), perpendicular to the ice dams. The whole idea of placing them perpendicular to the ice dams is to create drainage channels for water, so water doesn't back up in to your house.
I tried this on a cold January day at my neighbors house (thanks for being a willing participant, Jonathan). I was also curious as to what magical properties the pantyhose possessed. How do pantyhose make salt so much more effective than salt alone? Wouldn't it work a lot faster to just put salt directly on to the ice dam? As it turns out, yes. This works way better.
The photos from my little experiment are below. I filled one of the pantyhose up with "Ice Melt", which contained a blend of calcium chloride and rock salt. I filled the other pantyhose with an ice melting salt that didn't have the contents labeled - I suspect it was just rock salt. I also poured the Ice Melt in a perpendicular line along the ice dam, using far less salt than I used in either of the pantyhose.
10:00 AM (Start Time)
Hmm... it looks like we have a winner. If you're going to put salt on your roof, I don't understand what the purpose of using pantyhose is. The obvious thing here is that salt applied directly to an ice dam is far more effective than salt in a pantyhose. So you can run and tell that.
Reuben Saltzman, Structure Tech Home Inspections