Why snow slides off a metal roof all at once
Metal is smooth, and its painted finish is slicker still. On a sunny day, or when the attic warms the roof deck, a thin layer of water forms under the snow and the whole pack lets go together. On shingles snow creeps and melts in place. On metal it comes down in one heavy slab, sometimes with ice in it, and it moves fast.
Which side of the house matters. South and west slopes get the sun and tend to slide on the first warm afternoon after a storm. North slopes hold snow for weeks, then drop it all during a thaw or a rain. Either way, the slide often comes while people are outside shoveling.
That's the point of a metal roof in snow country: it sheds. Snow guards decide where it sheds.
Where snow guards go on a metal roof
Put them anywhere a slide would hurt someone or break something:
- Above entry doors, steps and walkways
- Over decks, porches and patios
- Above a lower roof, so the upper roof doesn't dump onto it
- Along a driveway or wherever cars park
- Over gas meters, AC units and plumbing vents
Gutters are the other reason. A slide can rip a gutter off in one go, so if you want gutters on a metal roof, you want snow guards above them.
Clamp-on vs pad-style snow guards
Clamp-on guards attach to the raised seams of a standing seam metal roof with set screws, so nothing pierces the panel. Most are a rail or bar that runs across the roof, and some can be matched to the roof color. They're the cleanest choice for standing seam.
Pad-style guards are small individual cleats spread across the roof in a staggered pattern. On ribbed, exposed-fastener panels they're usually screwed through the panel into the framing with sealing washers. On metal shingles they're shaped to fit the shingle. They hold snow in place across the whole slope rather than at one line.
Neither style is better everywhere. Seam type, pitch and where you need the snow held decide it.
Adding snow guards to an existing metal roof
You don't need a new roof to get snow guards. Clamp-on systems go straight onto existing standing seam, and pad-style guards can be added to ribbed roofs as long as they're fastened into solid framing. The work has to happen on a dry, clear roof, so fall is the time to book it, not the week after the first big slide.
On ribbed roofs, every pad has to land on a purlin or rafter, not just the thin steel between them, and each screw gets a sealing washer like the rest of the roof. A screw that misses the framing can pull out under a heavy snow load and leave a hole behind. After the first real snowfall, walk around the house and look at how the snow is sitting; uneven loads show where another guard is needed.
If an old slide already bent gutters, trim or vent pipes, have those fixed in the same visit. Our metal roof repair page covers what usually needs attention.
Snow guards, ice dams and upstate winters
Snow guards and ice dams are related but not the same problem. Ice dams form at cold eaves when heat from the house melts snow higher up and the water refreezes at the overhang. A metal roof sheds most snow before that gets bad, but once you hold snow in place with guards, the eave has to be right: ice and water barrier under the panels at the edge, and an attic that isn't leaking heat.
How much snow you're holding back matters too. A roof in Saratoga Springs and one north of Lake George or up in Warrensburg see very different winters, and snow sits longer on shaded north slopes and under tall pines. The installer sizes and spaces the guards for that, which is why one product and one row isn't the answer for every roof.