On Feb 19, 3:53 pm, "Mamba" wrote:
An unusual snow load this year took out the vent pipe off my steep metal
roof. Since we rarely get big snow and the roof normally sheds it quickly,
I hadn't seriously considered a snow dam or similar device until now.

I checked at the local building supply store, and the "dam" product they
sell appears to be a piece of heavy flashing with a 90 angle to form a ledge
about 2" high. Not very impressive, and no profile to match that of my roof.

With a vent pipe extending 18" above the roof line, I would expect the dam
to stop the bottom 2" or so, and potentially the upper layers could slide
over it and take the pipe out again. The snow would have about 20' of roof
to gain momentum.

So I am considering an alternate device, something like a few very stout
"pegs" in an inverted Vee shape above the vent pipe. My theory is that snow
or ice could come down but then be split up or diverted by the set of pegs.
They could be 6" or so high, perhaps galvanized lag bolts with a short
length of 3/4" pipe around them. Perhaps a total length of 6" or so. I even
have paint to match my metal roof color!

Looking for opinions on whether this might/not work.

Cheers

Kind of depends on how much snow you are talking about. In the
cascades in Washinton, I've seen snow bend the edge of heavy gauge
steel roofing right over the eave, and would snap an ordinary plumbing
vent like a match stick (vents would have to be cast iron and pierce
the roof at the peak). I guess I think your idea will work, but you
are going to have to engineer it to be pretty stout. Also, the snow
will probably just hang up and stay up there, which maybe isn't so bad.