Grade-Level Door

A grade-level door is a commercial overhead door set at ground level, so its threshold sits flush with the parking lot outside and the floor inside. Vans, pickups, box trucks, forklifts and equipment drive straight through it. That is why it is also called a drive-in door. Its opposite is the dock-high door, which sits up at truck bed height so a trailer can back against it. A building with both uses the dock doors for semi trailers and the grade-level door for everything that has to roll in on its own wheels.

Grade-level door vs dock-high door

• Where the floor is. A grade-level door opens onto pavement at the same height as the floor. A dock-high door opens onto a raised platform, most often 48 to 52 inches above the truck court, with a dock leveler to bridge the last few inches to the trailer.
• What uses it. Creative Door, a commercial door company, sums it up: dock-high doors line up with the trucks, while drive-in or grade-level doors let forklifts enter the building directly without a ramp or a dock door. A semi trailer cannot load at a grade-level door unless the yard has a ramp or a portable plate.
• What goes around it. A dock door is sealed to the trailer with a dock seal or shelter and bumpers. A grade-level door has no trailer to seal against, so it seals to the slab with its own bottom seal and to the jambs with weatherstrip, like a very large garage door.
• Size. A grade-level door is sized to the biggest vehicle that drives through it, plus room on each side and above, so it is usually wider and taller than the dock doors on the same building. There is no single standard size. Measure the clear opening, the headroom above it and the side room, and size the door from those.

What kind of door goes in a grade-level opening

Any of the main commercial door types can serve a drive-in opening. The choice comes down to headroom, traffic and climate.

• Sectional doors store flat under the ceiling on horizontal track. An insulated sectional door is the usual pick for a heated shop or service bay.
• Rolling steel doors coil into a barrel above the opening, so they suit openings with little headroom or a ceiling full of lights, cranes or ducts. The curtain of interlocking slats also stands up well to knocks.
• High-speed doors open and close in seconds. They fit a drive-in opening that cycles all day, because a door that is open for less time loses less heat. See high-performance door.

What a grade-level door has to put up with

A drive-in door lives in the path of traffic, so it takes more wear than a dock door that only opens to a parked trailer.

• Vehicle hits. A forklift mast or a truck mirror catching the bottom bar, a guide or a jamb is the most common damage. A bent guide or track makes the door bind or come off track. Bollards or guide guards at each jamb keep a small bump from becoming a new door.
• The bottom seal on the slab. The door closes on the floor, so a worn or torn bottom seal, or a slab that has settled or slopes, leaves a gap for wind, snow and water. A new seal and a sound bottom seal retainer close most gaps. In a Colorado winter, meltwater can freeze the seal to the slab, and running the operator against it strains the door.
• People and vehicles in the same opening. Workers walk through drive-in doors that vehicles also use, so the entrapment protection on the operator matters. Under UL 325, commercial door operators use monitored safety devices such as photo eyes or a sensing edge. A separate pass door beside the big door keeps foot traffic out of the vehicle lane.
• Wind. A wide door on an outside wall catches a lot of wind. Wind-rated doors use heavier struts or windlocks to stay in their track.

Ramps and drive-in docks

Some buildings use a sloped approach so a grade-level door can also serve smaller trucks, or a ramp up to a dock door for forklifts. The slope has limits. Blue Giant, a loading dock equipment maker, puts the steepest workable grade from dock to vehicle at 10% for electric handling equipment and 15% for gas or diesel equipment, and warns that a steeper grade can hang up equipment and spill loads. It also lists vehicle bed heights from 30 to 62 inches, which is why a grade-level door, with no bed height to meet, is the simpler opening for vans and pickups.

Adding or converting a grade-level door

Turning a dock door into a drive-in door, or cutting a new grade-level opening, means changing the wall, the header and often the slab or the approach outside. That is building work and usually needs a permit; see commercial garage door permits in Denver. The door itself is the last step: once the opening is framed, the door, track or guides, springs and operator are chosen for its size and use.

Grade-level door service in Lakewood and Denver

G Brothers works on rolling steel, sectional, high-cycle and fire-rated doors for warehouses, storefronts and loading docks across the Denver metro, on every brand and operator type, and installs and services high-speed roll-up doors. Business customers can get a certificate of insurance, usually within 24 hours. For a drive-in door that was hit, binds in its guides or will not seal at the floor, see commercial garage door repair or rolling steel door repair. For a new or bigger opening, see commercial garage door installation. Or ask for an estimate.

Sources

• Creative Door, Warehouse Docks, Doors and Equipment Basics Explained
• Blue Giant, Planning and Design: Dock Height
• Blue Giant, Planning and Design: Door Size