Bar grating is one of those items that seems simple until it deflects underfoot or fails an inspection. Specifying it well takes three decisions: how much load over what span, what surface, and to what standard. Get those right and grating is a durable, low-maintenance floor. Get them wrong and it is a trip hazard or a callback.
What is bar grating and where is it used?
Bar grating is an open steel grid made of load-bearing bars running in the span direction, joined by cross bars. The open surface is the point: it drains water, sheds debris, and lets air and light through, which is why it dominates industrial and exterior applications.
You will find it as equipment platforms and catwalks, mezzanine floors, crossovers and access walkways, trench and pit covers, and stair treads. It is a core item in the miscellaneous metals package, and like the rest of that scope it gets missed when no single sub owns 05 50 00.
How do load classes work?
Grating is sized by matching the bearing bars to the span and the load. Two variables do most of the work: how deep the bearing bars are, and how closely they are spaced. Deeper, more closely spaced bars carry more load over longer spans with less deflection.
| Duty | Typical use | What drives the spec |
|---|---|---|
| Light pedestrian | Walkways, access platforms | Foot traffic, comfort deflection limit |
| Cart and dolly | Maintenance platforms, mezzanines | Concentrated wheel and equipment loads |
| Vehicle or heavy | Trench covers in drive areas | Wheel loads, dynamic impact |
The clean way to do this is to give your fabricator the clear span and the loads, and let them select bearing bar depth and spacing from the load tables. Do not eyeball it. Deflection, not just strength, is usually what governs comfort and code compliance.
Serrated or smooth: which surface?
The surface choice is about slip resistance versus cost and cleaning.
- Serrated grating has notched teeth along the top of the bearing bars that grip footwear. Specify it where surfaces get wet, oily, greasy, or icy, on exterior platforms, and wherever the governing code or the owner’s safety standard requires slip resistance. It costs slightly more and marginally reduces open area.
- Smooth grating is easier to clean, slightly cheaper, and fine where slip risk is genuinely low, such as dry interior areas.
When in doubt on an industrial or exterior platform, serrated is the safe default. The small premium is cheaper than a slip incident.
What is MBG 532 and why specify to it?
ANSI/NAAMM MBG 532, the Metal Bar Grating Manual, is the industry standard from the National Association of Architectural Metal Manufacturers. It defines grating types, bar sizes and spacings, standard designations, and load and deflection tables. Specifying grating to MBG 532 means the product has known, published structural behavior rather than an unverified assumption.
Practically, specifying to MBG 532 lets you or your engineer read a load class straight from a table, gives the fabricator an unambiguous target, and gives the inspector a standard to check against. It is the difference between “some grating” and grating that provably carries its duty.
What to confirm before you buy
- Span and load per location, so bearing bars are sized, not guessed.
- Serrated vs smooth, driven by slip exposure and code.
- Material and finish: plain, galvanized, or coated for coastal and corrosive settings.
- Banding, cutouts, and attachment, so panels fit openings and are properly fastened.
TMG fabricates and installs bar grating, platforms, and stair treads as part of its miscellaneous metals scope, sized to your spans and loads and coordinated with the structural steel and access framing. For the posts that protect those platforms and equipment, see the pipe bollards guide.