Drainage Grates& Covers

Drainage grate load ratings follow EN 1433 numeric classes, which the US market cross-references with AASHTO H-20/HS-20 truck loadings: A15 (~3,372 lb) is pedestrian, plaza, and sidewalk duty. B125 (~28,100 lb) covers walkways and light-vehicle parking. C250 (~56,200 lb, roughly AASHTO H-20) suits car and light-truck parking lots. D400 (~89,900 lb, roughly AASHTO HS-20/H-25) handles roadways, forklifts, and loading docks. E600 (~134,900 lb, roughly HS-25) is for industrial yards and docks. F900 (~202,300 lb) is airport apron and port duty. Always select a class that exceeds your actual wheel loads.

They are all drainage grates, but they fit different structures. A storm drain grate (also called a storm drain cover or inlet grate) caps a curb or area inlet that feeds a municipal or site storm sewer and is usually cast iron or ductile iron rated for vehicle traffic. A catch basin grate is round or square and sits over a sump that traps sediment before the outlet pipe. A trench drain grate (channel grate) is a long, narrow cover that runs the length of a linear channel. When ordering a replacement, measure the inside frame opening and match the grate type, size, and load class to your existing structure.

Cast iron (gray iron) is more brittle and prone to cracking under impact but is less expensive and adequate for lighter loads. Ductile iron contains nodular graphite that makes it more flexible, impact-resistant, and able to deform without fracturing. Ductile iron has 2-3x the tensile strength of gray iron and is required for heavy-traffic applications. For Class C and above load ratings, ductile iron is strongly recommended.

Stainless steel grates are essential in corrosive environments: food processing facilities, commercial kitchens, breweries, pools, coastal areas, and anywhere exposed to chemicals or salt. They also provide a premium appearance for visible installations. The higher upfront cost is offset by dramatically longer service life—stainless won't rust, corrode, or require replacement like carbon steel or iron grates in harsh conditions.

Section 302.3 of the 2010 ADA Standards for Accessible Design sets two rules for grates in walking surfaces: openings may not allow passage of a sphere larger than 1/2 inch (13 mm), and elongated openings must be placed with the long dimension perpendicular to the dominant direction of travel. In practice, any grate on an accessible route—sidewalk, plaza, curb ramp, accessible parking—needs slot widths of 1/2 inch or less regardless of orientation. Heel-proof grates go further, typically 5/16 inch (8 mm) or narrower, to keep narrow heels, cane tips, and bicycle tires from catching.

Those are metric callouts in millimeters, listed length first. A 1000x300 grate measures 39.4" x 11.8"—a one-meter trench grate section for a nominal 300 mm (12") channel. A 960x600 grate measures 37.8" x 23.6", a large rectangular gully or inlet grate; the closest common US frame is 36" x 24" (914 x 610 mm), but the two are not drop-in interchangeable, so always match the clear opening of your existing frame. To convert any metric grate size, divide the millimeter dimension by 25.4 to get inches.

Measure the inside dimensions of the frame or basin opening—this is the seated grate size. Common sizes include 6", 9", 12", 18", and 24" for catch basins, and standard widths for trench drains. Also measure frame depth if replacing both frame and grate. When possible, identify the manufacturer and model number of your existing system, as grates are designed to fit specific frames and may not be interchangeable between brands.

Open area percentage determines water intake capacity: Slotted grates (60-70% open) provide maximum intake but may not be heel-safe. Perforated grates (40-50% open) balance intake with heel safety. Bar grates offer high structural strength with moderate intake. Lattice/grid patterns combine aesthetics with functional drainage. For high-flow applications, specify grates with the highest open area that still meets your load and safety requirements.

Locking grates are recommended or required for: public areas where theft or tampering is a concern, safety-critical locations like playgrounds or schools, traffic areas where vibration could dislodge grates, and anywhere unauthorized access to the drainage system must be prevented. Locking mechanisms include bolt-down hardware, hinged frames with locks, and specialty tamper-resistant fasteners.

Tree grates are decorative grates installed around the base of trees in urban environments. They protect tree roots from foot traffic and compaction, allow water and air to reach the root zone, provide a stable walking surface, and enhance streetscape aesthetics. Tree grates come in various patterns (concentric rings, radial designs, custom logos) and can include expandable centers to accommodate tree growth.

Grate rattle occurs when grates aren't properly seated in frames. Solutions include: using rubber gaskets or neoprene strips between grate and frame, ensuring frames are installed level and true, selecting grates designed with noise-reducing features (machined bearing surfaces, tight tolerances), using bolt-down or wedge-lock systems to secure grates, and specifying solid-top frames where high traffic is expected.

Many decorative grate patterns are available in load-rated versions suitable for vehicle traffic. However, intricate patterns may have lower structural strength than simple bar or slot designs. When specifying decorative grates for traffic areas, always verify the load rating meets your requirements. For heavy-duty applications, consider using decorative patterns only in pedestrian areas and functional designs in drive lanes.