Roof Avalanche: Doorways, Walkways, Gas Meters and What Sits Below the Eave
A slab release from a metal roof arrives in one place, all at once, with real force. Planning for it means reading the roof plan against what is on the ground before the panels go on.
The word sounds dramatic for a house, but it describes the event accurately. Snow that has consolidated on a metal roof releases as a coherent slab, travels down a low-friction slope, and lands in a defined zone below the eave. It happens quickly, usually without warning, and often on a sunny day when the weather seems benign. Deciding what to do about it starts with reading a roof plan against what is actually on the ground.
It Is a Release, Not a Snowfall
The distinction matters because it changes what you are protecting against. Falling snow arrives gradually, spread over a wide area, and does no damage. A slab release delivers a season's accumulation from a defined area of roof to a defined strip of ground in a few seconds. The mass involved is significant, particularly after freeze-thaw cycles have consolidated the pack and rain events have added water, and it can carry an ice layer at its base. Whatever occupies that strip of ground receives all of it at once.
Reading the Roof for Discharge Zones
Every roof plane discharges over its own eave, so mapping the hazard means tracing each plane to where it ends and looking at what is below. A simple gable roof has two zones. A complex roof with hips, dormers, additions and lower sections can have a dozen, and some planes discharge onto other roofs rather than onto the ground. The exercise is worth doing on paper before panels are ordered.
- ✓The front entrance, side door, and back door, plus the landing and steps at each.
- ✓The walkway from the driveway, and any path that gets shovelled and used daily.
- ✓The gas meter and its regulator, along with the service piping into the building.
- ✓Sidewall vent terminals for high-efficiency furnaces, boilers and water heaters, and any fresh air intake.
- ✓Air conditioning condensers, heat pumps, generator enclosures and their pads.
- ✓Eavestroughs, downspouts, and any downspout extension or splash block.
- ✓Decks, railings, stairs, hot tubs, awnings, pergolas and permanent furniture.
- ✓Lower roofs: porches, bay windows, garages, additions, sunrooms and covered entries.
- ✓The property line, where discharge would land on a neighbouring property or a public sidewalk.
Gas Meters and Vent Terminals
This is the item that gets underestimated most often, and it has the most serious consequences. Gas meters and regulators are mounted on exterior walls, frequently directly under an eave, and utilities have clearance requirements around them for exactly this reason — ice and snow loading on a meter set is a safety issue, not a cosmetic one. Sidewall vent terminals for high-efficiency appliances matter just as much: they are typically PVC pipes penetrating a wall above grade, and a slab landing on them can break, block or bury the intake and exhaust, which affects the appliance inside. Both should be identified on the roof plan and protected with retention above them, and where a meter or terminal cannot be protected, the utility or the mechanical contractor should be consulted about relocation.
Eavestroughs and the Edge
Eavestrough on a metal roof lives in a hostile position, since everything the roof sheds passes over it. Trough set too high relative to the panel edge catches sliding snow and gets torn off the fascia; trough set below the projected slide line lets snow pass over. Hanger type and spacing and the position of the drip edge and eave trim all figure into it, which is why eavestrough is part of the metal roof conversation.
The Two-Storey Unload
The most consequential discharge path on many houses is not to the ground at all. An upper roof that discharges onto a porch roof, a garage roof, an addition or a sunroom delivers its accumulation onto a structure that was framed for its own snow load, not for that of a larger roof above it. The lower roof also then has a deeper pack sitting on it for the rest of the winter. Where this geometry exists, retention on the upper roof is the usual answer, and where the lower roof is lightly framed or of unknown construction, its capacity is a question for a structural engineer.
Three Ways to Deal With It
Retention is the primary control: hold the snow on the roof so it melts and discharges gradually, using an engineered layout above the areas that need protection. Protection is the secondary control: diverters and crickets above specific obstructions such as a chimney or a vent terminal, canopies or porch roofs over entrances designed to take the load, and guarding around equipment. Relocation is the third and is sometimes the cleanest: move the walkway, move the air conditioner, move the parking, and where the utility permits it, relocate the meter. On most projects the answer is a combination — retention over the entrances and the meter, a diverter above a specific penetration, and an accepted discharge zone over the lawn where nothing needs protecting.
Diverters are for small obstructions such as a plumbing stack, a vent terminal or a chimney. They split snow around an object; they do not stop it. Protecting a doorway, a walkway, or a lower roof requires retention that holds the snow on the slope, not a device that steers it a metre to one side.
Solar Arrays
Solar panels create their own version of the problem. The array surface is smooth glass, often at a slightly different angle to the roof plane, and it sheds independently — sometimes onto the metal below it, which then discharges over the eave. The racking also creates edges where snow catches and drifts. Where an array is planned, retention layout, racking layout and discharge paths have to be worked out together.
What We Walk Through on Site
Before a metal roof is specified we trace where each roof plane discharges: entrances and the paths people actually use, the gas meter and any sidewall vent terminals, mechanical equipment, the eavestrough detail, any lower roof in a discharge path, and the property line. That produces the retention plan, the diverter locations, and an honest conversation about where the answer is to accept the discharge and keep the area clear.
Frequently Asked Questions
How far does snow travel when it comes off a metal roof?
It depends on the roof height, the slope, the mass of the slab and how much speed it picks up, so there is no single distance. The practical assumption is that discharge lands in a zone extending out from the eave rather than straight down, which is why the area beneath an eave — not just the drip line — is what gets assessed.
Can snow from a metal roof damage a gas meter?
Yes, which is why utilities specify clearances around meters and regulators and why retention above a meter set is standard practice. Ice and snow loading on a regulator is a safety concern. If a meter sits directly beneath an eave that cannot be protected, the utility should be asked about relocation.
Will snow sliding off damage my eavestrough?
It can, and it does when the trough is positioned so that sliding snow catches it. The way to avoid it is to detail the eave, the drip edge and the trough position so the discharge passes over the trough rather than into it, and to use hangers appropriate for the loading. It is a detail worth settling during the roof design, not afterward.
Should I put snow guards over my whole roof or just above the door?
Retention rows generally run the full width of a roof plane, because a partial run lets adjacent snow slide around the ends and loads the ends of the run unevenly. Which planes need retention at all is decided by what is below each of them, but on a plane that needs it, the row normally runs across.
Is a roof avalanche a reason not to choose metal?
No — it is a reason to plan the discharge before installation. Snow retention, diverters, eave detailing and, where needed, relocating what sits under an eave are established solutions to a known behaviour. The problems come from installing a shedding roof over an unexamined property, not from the roof itself.
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