Snow removal for parking garages: top decks, load limits and the concrete underneath

Why is a parking garage different from a lot?

The top deck is a roof that cars park on. It takes the full snowfall, and every pound a plow moves stays on the structure. Lower levels get blowing snow at the open sides and ramps, plus the slush and street salt cars carry in.

The deck is also more fragile than it looks: concrete with reinforcing steel or post-tensioning inside, sealed expansion joints and, often, a traffic-bearing membrane. The American Concrete Institute's parking structure maintenance guide (ACI PRC-362.2-21) notes that they can develop more distress than most buildings because they are directly exposed to traffic, weather, deicing chemicals and snowplows.

What gets cleared first, and by when?

SIMA, the snow management industry association, tells contractors to always clear and treat entrances, exits, stairs and ramps. Hospital and transit garages may need ramps and stairs held to a zero-tolerance standard.

What equipment can run on the deck?

Ask the structure's engineer, in writing, before the first storm. Walker Consultants, a parking structure engineering firm, tells owners to know the structure's weight limits, know the snow equipment's weights, and use small equipment on the roof level. Get limits for each level: the heaviest machine allowed, and whether a skid steer, a tractor with a blower or any loader may run at all. No heavy loader goes on a deck without the engineer's okay.

Sika, which makes deck coatings, asks owners to post signs banning tire chains and studded tires on its coated decks; that goes for snow equipment too. Check the clearance bars as well: a truck carrying a spreader may not fit under the entrance.

Why can't snow be piled on the deck, and where does it go?

Because a pile concentrates weight on one spot. Walker says the most common reason for snow-related deck collapses is plowing and piling: plowing densifies the snow, the denser snow goes into big piles, and those concentrated loads are much heavier than cars.

The numbers show why. The International Building Code's minimum uniform live load for passenger-vehicle garages is 40 pounds per square foot. Heavy, wet snow weighs about 12.5 pounds per square foot for every foot of depth before a plow packs it (heavy wet snow vs light snow), so a six-foot pile puts roughly 75 pounds on each square foot beneath it, nearly double. The real capacity is in the structural drawings. If a deck shows sagging, new cracks or ponding where it used to drain, treat it like an overloaded roof; see roof snow load warning signs.

That leaves three ways to handle top-deck snow:

1. Leave it. If the parking can be spared, Walker's simplest advice is to close the level and let it melt.
2. Move it with light equipment to a spot the engineer has approved, and remove it between storms.
3. Drop it over the edge only into a barricaded, cleared area below, with the owner's permission, as SIMA advises.

How do you protect joints, membranes and drains?

• Cutting edges. SIMA recommends rubber or polyurethane cutting edges to protect finished surfaces, expansion joints and coatings. Sika's vehicular deck coating guide says to avoid metal blades and fit plows and buckets with rubber blades and plastic runners or shoes.
• Joints. SIMA warns never to push snow up against expansion joints or architectural details, to keep blades at least half an inch above them, and to slow down at ramps and changes in slope.
• Markers. Stakes cannot go into a deck, so mark hazards with cones, delineators or paint before the first storm: joints, drains, wheel stops, speed bumps, column bases, gate curbs and the barrier walls at the open edges, all on the site map.
• Drains. Keep every floor drain open so meltwater leaves the deck instead of ponding and refreezing, and never stack snow over a drain.
• Spring. Sika asks owners to rinse coated decks with clean water after each winter to remove residual salts.

Which deicer is safe on a parking deck?

The one the engineer or the coating maker approves, in writing. ACI's guide warns that, unless the deck is protected from deicer intrusion, chloride-bearing deicers such as salt may accelerate corrosion of the embedded reinforcing steel and hasten deterioration, and that cars carry street salt in anyway. Salt brine is hard on a home garage floor, too; a parking deck adds structural steel inside the slab.

Coated decks follow the coating maker's list; Sika, for example, says its vehicular systems resist standard calcium chloride and sodium chloride. Whatever the product, keep it to ramps, entrances and walking routes, and do not over-apply: SIMA warns that over-salting can damage concrete, joints and drainage.

Records and contract questions

SIMA calls documentation (when work started, when it finished and what was done) the first line of defense against slip-and-fall claims. For a garage, also log the equipment used on each level, the deicer and rate, and any contact with a joint or membrane, with photos. See snow logs. Before signing for commercial snow removal, ask:

1. What are the engineer's equipment limits for each level, in writing?
2. What cutting edges and shoes will the equipment wear?
3. Where does the snow go, and is edge discharge allowed with a secured area below?
4. Which deicers, at what rate, has the engineer or coating maker approved?
5. Who keeps drains open, and who rinses the decks in spring?
6. Are joints, drains and membrane edges on the site map?