Do Metal Roofs Need Snow Guards in Washington?

Do metal roofs actually need snow guards?

Often, and this deserves a straight answer rather than a reassuring one. The same smooth interlocked surface that keeps snow from piling up is what allows an accumulated pack to release in one movement once the interface warms. Wet Cascade snow is heavy, and a slab of it coming off a second-storey roof plane is a real hazard. That is not an argument against metal roofing. It is an argument for designing the roof with the release in mind. Snow retention is a routine part of specifying a metal roof in snow country, and leaving it out is the mistake, not including it. The decision is site-specific. Two houses in the same town can reach different answers depending on slope, orientation, roof geometry and what sits underneath the eave.

What do snow guards do, and what do they not do?

Snow guards, sometimes called snow retention devices or snow fences, hold accumulated snow on the roof surface so it melts gradually and drains through the gutter system rather than releasing as a mass. They convert a sudden event into a slow one. What they do not do is remove snow, reduce the weight on the structure, or make an under-framed roof safe. Holding snow in place means the load stays on the roof longer, which is why retention has to be considered alongside the structure rather than as an afterthought bolted on at the eave. They also do not eliminate ice at the eave. Ice dams are caused by heat escaping into the attic, and retention devices do not address that mechanism. Ventilation and insulation do, and that is treated separately in this series.

Where on the roof do snow guards belong?

Above anything that a sliding slab would hit. That means entry doors and porches first, then walkways, driveways and parking areas, decks and patios, and stairs. It also means service equipment: gas meters, heat pumps, condensing units, propane tanks, vents and satellite dishes mounted on a lower roof. Pay attention to lower roof planes that sit beneath a larger upper plane. Snow released from above lands with force on a smaller roof that was never intended to take an impact load, and that is a common source of damage on complex rooflines. Gutters deserve a mention too. A sliding pack will take a gutter with it if the mass is large enough, and on long uninterrupted runs the released load can be considerable. Retention placement is normally driven by these ground-level and lower-roof consequences rather than by a uniform rule applied to the whole roof.

Which Washington homes usually need snow guards and which do not?

Homes in the Cascade foothills usually do. North Bend, Snoqualmie, Enumclaw, Buckley, Granite Falls and Darrington on the Snohomish side, and Morton, Randle and Packwood south along the corridor, all see accumulations that can release as a mass. Elevation matters more than the town name; a house partway up a grade sits in different conditions from one at its base. Lowland Puget Sound homes frequently do not need retention. Central Seattle, Tacoma, Everett, Bellevue and the shoreline communities on the Salish Sea see snow that rarely accumulates enough or lingers long enough to release dangerously. The practical test is simple. Look at each roof plane, follow its slope to where snow would land, and ask what is there. If the answer is a lawn or a planting bed, retention is optional. If the answer is your front door, your driveway or the deck where people sit, plan for it. Interlock has completed 3,223 Washington installations since 1997 across both of these climates, and the retention answer is not the same in both.

How are snow guards fitted to an interlocking aluminum roof?

They are planned before the panels go on. On a concealed-fastener interlocking system the retention detail is coordinated with the panel layout and installed as the roof is laid, using the method the manufacturer approves for that system, so that attachment does not compromise the water-shedding path or the panel interlock. That sequencing is the point worth taking away. Retrofitting retention onto a finished metal roof is more difficult than including it in the original scope, and improvised attachments, particularly adhesives or fasteners not specified for the panel, can create leak paths or void coverage under the material warranty. So raise it during the estimate. Walk the roof planes with your installer, mark the locations where a slide would land somewhere that matters, and get the retention shown on the plan and priced in the contract before work begins.

Common questions