The Lower Mainland gets little snow (Vancouver averages about 37 cm a year, the valley and the North Shore more), but what it gets is wet, heavy and followed by a thaw, which is exactly the combination that slides off a metal roof in one sheet and builds ice dams at a north-facing eave. Snow guards are cheap insurance on any metal roof over a door, walkway, deck or driveway. Ice dams are an insulation and ventilation problem with a roofing symptom. Here is what each needs.
Why metal roofs need snow guards here
A smooth standing seam or metal shingle roof holds snow until the layer against the metal melts, then releases the whole slab at once. A few centimetres of wet coastal snow over a 400 sq ft slope weighs hundreds of kilograms. It lands on whatever is below: the front steps, a parked car, a gas meter, a heat pump, the gutter (which it rips off), a lower roof, or a person. The snow retention industry's own position is that there's no way to predict a rooftop avalanche, which is why guards go on before the first winter, not after the first incident.
Types of snow guards
| Type | How it works | Fits | Notes |
|---|---|---|---|
| Clamp-on bar systems | Continuous aluminum bar in clamps that grip the standing seams, no holes in the roof | Standing seam | The engineered option; clamps are tested for each seam profile |
| Pad-style guards (individual cleats) | Small pads glued or fastened in rows across the slope | Standing seam, metal shingles, exposed-fastener panels | Cheaper; glued pads depend on adhesive and surface prep; fastened pads mean holes |
| Fence systems | Rails on brackets, like a bar system | Any metal roof | Common on commercial roofs |
| Bent-metal stops | Simple sheet metal angles screwed down | Exposed-fastener panels | Snow industry sources note they often bend, fold and collapse under load |
Clamp-on systems from engineered manufacturers (S-5! ColorGard is the widely known one) are what roofers specify on standing seam because the clamps grip the seam without penetrating the panel and the loads are calculated. Pad-style guards are fine in rows above a doorway on a shingle-profile metal roof. Whatever the type, guards go over the areas where falling snow does harm: entrances, walkways, decks, driveways, lower roofs, utilities and gutters.
How much snow retention do you need?
Snow guards are engineered to the roof's snow load, pitch, panel length and the number of rows. Metro Vancouver municipalities publish design ground snow loads around 2.6 to 2.9 kPa; Hope and the mountain slopes are higher. The guard manufacturer's calculator (roofers use them) takes those numbers and gives the row spacing. One row above the door is a guess; a calculated layout is a design. Ask the roofer for the layout and the product name in the quote.
Ice dams: what they are
An ice dam forms when snow on the roof melts from heat escaping the house, runs down to the cold eave (which overhangs unheated air) and refreezes. The ridge of ice grows, water backs up behind it, and finds its way under the shingles and into the wall and ceiling. The leak appears at the outside wall, often days after the snow.
They're less common here than in the Interior, but they happen in every cold snap, most on north-facing eaves of older houses with thin insulation, leaky ceilings and solid soffits.
Preventing ice dams
Ice dams are caused in the attic, not on the roof, so the fixes are mostly indoors:
- Air-seal the ceiling. Pot lights, the attic hatch, plumbing and wiring penetrations, the top of interior walls. Warm air leaking into the attic melts the snow.
- Insulate to current levels. The attic insulation rebates from BC Hydro and CleanBC ($0.02 per R-value per sq ft added, up to $900 and more depending on the program) help pay for it.
- Ventilate. Soffit intake and ridge exhaust to the 1-in-300 rule keep the deck cold so snow doesn't melt from below. See roof ventilation.
- Eave membrane. The BC Building Code requires eave protection (ice and water shield) at least 900 mm up from the edge on shingle roofs, except in regions with 3,500 or fewer degree-days, which covers all of the Lower Mainland. BC's roofing association and most roofers install it anyway, because when a dam does form, the membrane is what keeps the water out of the house. Insist on it in a re-roof quote.
- Drip edge and clear gutters. Ice in a clogged gutter is where many eave dams start.
Heat cables along the eave treat the symptom, cost electricity and look rough; they're a last resort on a roof whose attic can't be fixed.
What to do when a dam forms
Don't chip at it; you'll damage the shingles. Rake snow off the lower metre of the roof with a roof rake from the ground if you can reach safely. If water is coming in, a channel melted through the dam with calcium chloride in a sock (not rock salt, which corrodes) relieves the backup. Then fix the attic before the next winter. For an active leak, read roof leaks: what to do.
Snow and your roofing quote
Any metal roof quote should include snow retention over entrances, walkways and anywhere falling snow would do damage, with the product named. Any shingle roof quote should include eave membrane, drip edge and ventilation sized to the attic. The quote comparison guide lists both so you can check. If you're choosing between materials, the metal versus shingles guide covers how each handles snow.
Common questions
Do I need snow guards on a metal roof in the Lower Mainland?
Over doors, walkways, decks and driveways, yes: metal sheds snow all at once. On the North Shore, Westwood Plateau, Mission's hill and in Hope, where snow sits longer, more so.
Is eave membrane required here?
Not by the BC Building Code, which exempts regions with 3,500 or fewer degree-days, and every Lower Mainland municipality is below that. The roofing industry's standard still calls for it on shingle roofs, and good roofers install it in valleys and at the eaves.