What Snow Trigger Depth Does a Commercial Parking Lot Need?

Most commercial parking lots in Canada and the northern US are plowed once accumulation reaches a set trigger depth, usually 2 to 3 cm (about 1 inch) for retail, medical and high-traffic sites, and 5 cm (about 2 inches) for warehouses, yards and lower-traffic lots. Zero-tolerance service, where crews stay on site or return continuously during a storm, is reserved for hospitals, 24-hour operations and properties with steep ramps. The right number for your lot follows from who uses the property, when they arrive, and how the surface drains.

What a trigger depth is, and what it is not

The trigger depth is the accumulation at which your contractor is obligated to start clearing. It is measured on the ground, not forecast, and the contract should say where and how it is measured (a flat open area of the lot, not a drift against a wall and not a plowed lane).

Three things the trigger does not cover, and which need their own clauses:

• Ice and freezing rain. A quarter-centimetre of ice never reaches a 2 cm trigger. Salting and anti-icing need a separate, conditions-based trigger (surface temperature, freezing rain, refreeze after a thaw).
• Clear time. The trigger says when work starts. A separate clause should say when the lot must be usable, for example "cleared and treated by 6:30 a.m. on business days".
• Drifting and windrows. On open suburban sites in Laval, Mirabel or Mascouche, wind can bury a cleared lane under 10 cm with no new precipitation. Exposed sites should have drift clearing on request or on inspection.

The three common thresholds compared

2 to 3 cm (1 inch): standard for people-heavy sites

This is the threshold most retail plazas, clinics, offices, schools and multi-unit residential buildings in the Montréal area should be on. At 2 to 3 cm the snow is still light enough to push cleanly, so the surface comes up to bare pavement and salt works at low rates. Pedestrians have not yet compacted it into the glazed layer that causes most slip-and-fall incidents.

The trade-off is visit count. A 1-inch trigger brings a crew out for nearly every measurable snowfall, which in the Montréal region typically means 20 to 30 plow visits a season. On a per-push contract that adds up fast, which is why most properties on this trigger are on seasonal pricing.

5 cm (2 inches): standard for trucks, yards and low-traffic lots

A 5 cm trigger suits distribution centres, industrial yards, contractor lots, self-storage sites and overflow parking. Trucks and forklifts handle 4 cm of snow without issue, and fewer visits keeps the seasonal cost down. Plow visits in a typical season drop to roughly 12 to 18.

The risk is the pedestrian portion of the site. Even a warehouse has an employee entrance, a visitor lot and a path to the dumpster. A sensible contract applies the 5 cm trigger to the truck court and a 2 cm trigger plus salting to staff parking and walkways. Mixed triggers on one site are normal.

Zero tolerance: continuous service during the event

Zero tolerance means the contractor keeps the surface clear for the duration of the storm, either by staying on site or by cycling back at short intervals (often every 2 to 4 cm, or every two hours). It is the right choice for hospitals, dialysis and emergency clinics, long-term care homes, 24-hour manufacturing, transit lots, and any property with an underground garage ramp where even a thin layer defeats traction.

It is also the most expensive option by a wide margin, because the contractor dedicates equipment and an operator to your site for the full event rather than fitting you into a route. For properties that need it, the liability exposure justifies the cost. For a strip plaza that opens at 10 a.m., it is overkill.

How often each trigger actually puts a plow on your lot

Montréal-area winters produce a lot of small events and a handful of big ones. The pattern matters more than the seasonal total.

These are typical counts for planning, not guarantees. A winter with many 1 to 3 cm dustings widens the gap between a 2 cm and a 5 cm contract. A winter dominated by a few 30 cm storms narrows it, because both triggers get hit on the same nights. Salting visits are separate and often outnumber plow visits.

Matching the trigger to the property

Ask three questions about any site before choosing a threshold.

When do people arrive? A lot that fills at 7 a.m. needs the trigger paired with an overnight clear-time commitment. A lot that fills at noon can tolerate a later start and a slightly higher trigger.

Who walks on it? Elderly visitors, patients, children and anyone carrying things push the choice toward a lower trigger and more frequent salting. Truck drivers in work boots do not.

What is the grade? Any ramp, loading dock approach or sloped entrance should be its own zone with a lower trigger than the flat lot. This is the most common gap in snow contracts for multi-unit buildings in boroughs like Côte-des-Neiges or Saint-Léonard, where underground parking is the norm.

Contract language that makes the trigger real

A trigger depth is only as good as the clause around it. Look for, or ask for, the following.

• Measurement method. Where it is read, by whom, and whether the contractor's own log or a named weather station is the reference.
• Response time after trigger. "Crews dispatched within X hours of trigger being reached" is more useful than "prompt service".
• Clear-by time on business days. Tied to your opening or shift-change hour.
• Storm stacking. What happens when a second event starts before the first is cleared. Does the trigger reset? Is a second visit billed?
• Per-event documentation. Date, time in and out, depth at arrival, material applied. This is what defends a slip-and-fall claim, and most monthly invoices do not contain it. Our guide to per-event snow logging covers what the record should include.
• Separate ice trigger. Conditions-based, not depth-based, with a stated material and application rate.

If you are weighing per-push against seasonal pricing for a given trigger, our breakdown of commercial snow contract types explains how each model changes the incentive on marginal events. Properties in the northern suburbs can also review our Laval snow removal page for how storage and site layouts differ north of the river.

Frequently asked questions

How often should a commercial parking lot be plowed?

As often as accumulation reaches the trigger depth written into the contract. For most retail, office and medical lots that is every 2 to 3 cm, which in the Montréal area works out to roughly 20 to 30 plow visits in a typical season. Warehouse and yard lots on a 5 cm trigger see closer to 12 to 18. Salting visits are additional and are driven by ice conditions rather than depth.

Is a 1-inch or 2-inch trigger better for a strip mall?

A 1-inch (2 to 3 cm) trigger is the safer choice for any property with steady customer foot traffic, because it keeps the surface from compacting into ice between visits. A 2-inch trigger lowers the visit count and the seasonal price, but it shifts more of the safety burden onto salting and accepts that customers will walk on a few centimetres of snow during a storm.

Does a lower trigger depth cost more?

On a per-push contract, yes, because every extra visit is billed. On a seasonal contract the lower trigger is priced into the fixed fee, so the monthly cost is higher but predictable. For a site that needs the lower trigger, seasonal pricing usually ends up cheaper than paying per push for 25 or more visits.

Can different parts of one property have different trigger depths?

Yes, and they should. A common setup is a 5 cm trigger on a truck court or overflow lot, a 2 cm trigger on customer and staff parking, and zero tolerance plus pre-salting on ramps, stairs and main entrances. Each zone is listed in the scope with its own trigger, clear time and treatment.

Set the right trigger before the first storm

Tell us about your lot, how it is used and when it needs to be clear. We will recommend a trigger depth for each zone and price it as a seasonal or per-push contract. Start on our contact page and a Terranova coordinator will follow up with a site assessment.