Garage & Shop Floor Drainage
Drainage by Application · Home & Residential
Snowmelt dripping off parked cars, wash water with nowhere to go, rain blowing under the door — a garage or shop slab needs a drain the same way a driveway does. Here is how to lay one out, and which trench drain lines fit the duty.
Why garage and shop floors flood
A garage floor collects water from both directions. From outside: wind-driven rain and driveway runoff push under the door, especially when the apron pitches toward the building. From inside: two cars carrying snow or rain shed a surprising amount of water overnight, and any shop that washes vehicles, rinses parts, or hoses down the slab makes its own weather. Slab pitch alone rarely saves you — most garage floors are close to flat, and the door threshold acts as a dam that holds water in as effectively as it keeps water out.
In winter climates the stakes are higher than a damp floor. Meltwater that pools near the door refreezes overnight into a sheet at the exact spot where people step out of vehicles, and standing water left on a slab through freeze cycles works at the surface year after year. A floor that dries within the hour after cars come in is a safety measure as much as a convenience.
The fix is a trench drain: a linear channel set flush in the slab that intercepts sheeting water along its whole length and carries it to a piped outlet. Because the channel spans the full width of the opening or bay, it works no matter which direction the water arrives from — something a single round floor drain in a nearly flat slab can never promise.
Two ways to lay it out
Across the door opening. The classic residential placement: a channel spanning the garage door threshold, just outside or just inside the door line. It intercepts driveway runoff before it enters and catches anything draining off vehicles near the door. If the driveway pitches toward the garage, this is the placement that matters most.
Down the middle of the bay. The shop layout: the slab pitches gently from both sides toward a channel run in the middle of the floor, so wash water and drips find their way to it from anywhere in the bay. This is the arrangement for wash bays, detail shops, and any floor that gets hosed down deliberately.
Both layouts work in new pours and in retrofits — for an existing slab, a section is saw-cut out, the channel is set to grade, and concrete is poured back around it.
Choosing the right load class
Load class is decided by the heaviest wheel that will ever cross the grate, not the typical one. Per our Load Class Recommendation Guide, Class B (medium duty) is typically sufficient for residential driveways and light vehicle traffic — which covers home garages. Classes C and D meet the H-20 highway standard, making them the floor for anything that sees trucks, forklifts, or trailers: repair bays, equipment shops, loading areas. Remember that the rating that matters is the grate’s — the same channel often takes grates of several classes, and each grate’s class is listed on its product page.
Think about the apron, too. A threshold drain set at the door line lives half in the garage and half in the driveway, and it sees every wheel the driveway sees — including the occasional delivery truck. When in doubt between two classes at a threshold, take the heavier one; the cost difference is small next to replacing a cracked grate set in concrete.
The systems we recommend
NDS 5″ Pro Series
The go-to for a residential garage door threshold: a 5 in. channel that assembles in sections to span one, two, or three door widths, with a range of grate options to match the traffic and the look you want. Part of the broader NDS Pro Series family if you need a different channel width for the same project.
NDS Dura-Slope
The contractor-grade choice for shops and wash bays: a pre-sloped PVC channel system, so long runs keep water moving even in a dead-flat slab. Grates are available in multiple materials up to metal options for wheeled traffic. Buy it online by the section, or send us the run length for a project quote.
ACO KlassikDrain
Where the floor is a place of business — commercial repair bays, dealership service floors, municipal shops — ACO’s KlassikDrain family is the specification-grade step up, with grate options through the heavier load classes. ACO lines are quoted rather than carted: request a quote with your run length and duty.
ACO PowerDrain
For shop floors that carry forklifts, box trucks, or heavy equipment every day, PowerDrain is ACO’s heavy-duty sloped system, built for sustained vehicular loading. Quoted to your project — send the layout and we’ll spec channels, grates, and accessories together.
Josam Pro Plus channel drain systems are also available on request for engineered and spec-driven projects — ask us when you request a quote.
Match the line to the duty
| Floor | Typical traffic | Start with | How to buy |
|---|---|---|---|
| Residential garage threshold | Cars, foot traffic | NDS 5″ Pro Series | Add to cart |
| Detached shop / wash bay | Cars, light trucks, hose-downs | NDS Dura-Slope | Add to cart or quote |
| Commercial service floor | Trucks, daily vehicle traffic | ACO KlassikDrain | Request a quote |
| Heavy equipment / forklift bay | Forklifts, heavy vehicles | ACO PowerDrain | Request a quote |
Whichever line you land on, confirm the grate’s load class on its product page — grates, not channel bodies alone, carry the rating.
Before you tie in: where does the water go?
Clean storm runoff at a threshold can usually discharge like any exterior drain. But many jurisdictions treat interior floor drains — especially where oil, fuel, solvents, or wash water are in play — as sanitary connections that require an oil/sediment interceptor. Check with your local plumbing authority before connecting an interior run.
Garage & shop drainage FAQs
Can I add a trench drain to an existing slab?
Yes — retrofits are routine. A section of slab is saw-cut and removed, the channel is set to grade and piped, and concrete is poured back around it. New pour or retrofit, the channel ends up encased in concrete either way.
Which grate should I choose?
Match the grate to the heaviest wheel that will ever cross it. The grate carries the load rating, and each grate’s class is on its product page. Where vehicles cross daily, choose a metal grate.
Do I need a pre-sloped channel?
Short threshold runs are usually fine with the fall you set them at. Long runs in flat slabs benefit from a pre-sloped system like Dura-Slope, which builds the fall into the channel sections themselves.
Where should the water discharge?
Depends on what’s in it — clean stormwater and interior wash water are treated differently by most local codes. See the note above, and ask your plumbing inspector before tying in an interior drain.
Planning a garage or shop floor drain?
Send us the run length, load class, and what the floor sees — we’ll spec the right system and quote it same-day.
Buying for a home garage? The NDS 5″ Pro Series and Dura-Slope ship from stock. Prefer to talk it through? Call 803-324-3225, email [email protected], or use the contact form.