Garage Floor Drain

A garage floor drain is a great way to control water that spills onto the floor. It’s also useful for washing things inside the garage or cleaning the floor. Garage floor drains prevent water from soaking into your concrete or running onto the driveway. When the concrete floor is pitched into a drain, all of the water flows into the drain and away from the house. This helps keep the garage floor ad driveway clean dry. Without a drain, liquids can pool on top of the concrete until you clean them off or they soak in. Installing a concrete floor drain is fairly easy. They’re just like the drain in your shower. What you see is the floor drain grate, but what you don’t are PVC pipes under the floor leading water outside and away from your driveway.

The first step is to decide on the type of floor drain you want. They come in two basic types, a single round, square or rectangular shaped drain or a long thin trench. Trench drains are great when used by the door because they not only drain water away but also prevent water from getting in from under the garage doors. Many floor drains are piped with a simple P-trap, similar to what you find under most bathroom sinks. The U-shaped pipe beneath the drain provides a water seal, but it also enables debris to collect. Other designs simply divert water out much like a gutter without any complicated piping.

Check with your local building department for any code requirements before you install a garage drain. In most areas you can drain the floor drains to the outside surface of the home just like a gutter downspout.

Types Of Garage Floor Drains

There are a two main types of garage floor drains you can install. We’ll discuss both below.

Trench Drains

Trench drains are long, thin and rectangular. Typically they’re installed along the edge of the garage or by the doors. If positioned correctly, they can collect water that spills onto the floor and stop water from getting into the garage from outside. This is one of the biggest benefits of using a trench drain. Unlike a traditional floor drain, they protect the garage from water both inside and out.

Trench drains can also be very attractive. This depends a lot on the style grate you select because that’s the part you see. I really like the modern style grates with angular holes. We not only use them in the garage but also showers.

Trench drains are typically sold in pieces and assembled on site. This makes them a very versatile drain system. Some can be as short as a foot or two while others can easily span over 10 feet.

How Trench Drains Are Made And Assembled

Trench drains come in two basic parts, the drain and the grate. The drain area is typically set right into a concrete floor. Once in place the grate is laid onto the drain. Grates are generally removable so you can clean the drain later. Drains run into pipes and out of the garage just like a traditional drain system does.

Pro Tip: Make sure the drain doesn’t shift when the concrete floor is poured around it. Trench drains are more expensive than a basic floor drain and need more precision since they’re so long. The drain has to be level and pitched into the pipe in order for it to drain properly.

Trench drains come in either concrete or metal. I prefer the concrete variety with a galvanized or stainless grate. They’re strong and durable. You want a drain that can support a lot of weight because cars and trucks will be driving over it.

I would also recommend a drain that has the pitch built in so you don’t have to worry about creating the proper pitch yourself. Just install the drain level and you’re done.

You should not have water problems inside your garage if the trench drain is properly installed and the concrete floor has the right pitch. This is very important for any drain system you install. If the water doesn’t run into the drain then they won’t be very effective.

Bell Trap Drains

Bell trap drains are much simpler than a trench drain. They’re just a basic square or round floor drain in a single location. They’re easy to install, cheap and work really well.

Generally a bell style drain sits in the middle of the floor or in an area where you want to drain water. For example, if your building a wash area in your garage then that’s where you’d install the drain. They work just like a typical shower drain. Water runs into the drain and out through a pipe.

If your installing a bell trap drain in a new garage then the floors all need to pitch into the drain. This is harder to do than with a trench style. Trench drains only require the floors to pitch in a single direction.

When we install bell trap drains into existing garage floors we try to locate them in problem or work areas. Because you can’t easily re-pitch a concrete garage floor it’s best to put the drain where it’ll work. Most times the drains are installed in the center of the garage and water is swept in.

Pro Tip: Check the pitch of your floor before installing the drain. In a lot of cases the floors pitch in a way that they naturally flow into a single area. Even a slight unevenness effects how water moves even though you may not be able to see it. Once you find out where the water flows that’s where you install the drain.

As with a trench drain, install the floor drain level and make sure it doesn’t shift as you poor concrete around it.

How Much Does A Garage Floor Drain Cost?

A cheap 10 inch bell trap drain costs about $15 while an expensive one can run over $250. That’s just for the drain and grate. Custom grates will cost a lot more than that.

Once you buy the drain you’ll also have to buy pipe and fittings. Typically we use 3 inch – 4 inch PVC for this. I also like to get a cap for the end of the pipe so mice and other small animals can’t crawl in. Typically all the pipe comes to under $100 for an average 50 – 75 foot run.

Trench drains are much more expensive. The majority of them come in 3 foot pieces that you assemble yourself on site based on the size and layout you’ve got. They can range in price from $10 per lineal foot for plastic / polypropylene to 50 per ft. and up for concrete or metal.

Trench drains are very common in commercial applications so they get very heavy duty. Most large sites will have a 12 inch trench drain to deal with water. However in homes they’re usually around 4 inch. I’d expect to pay around $150 for a 10 foot section. Then you’ve also got the 3 inch -4 inch PVC pipe just like a bell trap drain to buy.

Trench drains have a lot more variety than bell trap because they can span long distances. Some people only need a few feet while others may need a 20 foot section. Custom grates for a trench style are very expensive because of how many square feet the grate takes up.

Installation costs will vary based on the job. If it’s a new construction job a typical install will run around $1500 bucks just for the drain. This does not include the concrete work. However, if your adding a drain to an existing floor expect to pay more for excavation, demo and repairs. Running a drain under an existing garage can be hard to do since access is limited.

Can You Install A Garage Floor Drain Yourself?

Yes. They’re really no that hard to install. It’s important to have a plan before you start working.

Figure out the location of your drain first. This is point A. Then determine where you’ll be draining all the water too. This is point B. Finally measure and plan out how you’ll run the PVC to get point A to connect to point B.

Remember that drains and pipes need to run down hill to work. If the floor drain pipe is 8 inches deep, then the outlet, point B, needs to be at least 13 -14 inches deep. I like to pitch about an eighth to a quarter inch per foot of PVC pipe running down hill.

You can do the demolition if it’s needed, dig the trench, install the drain pipe, and install the bell trap or trench drain all on your own. It involves a lot of time and labor, but it’s actually not that hard to do. Once the planning is out of the way and you figure out all your heights it’s just digging and running PVC.

There are two important things to remember when installing a floor drain on your own.

Make sure the pipe pitches down hill. You don’t want flat or back pitched sections of pipe because water can clog or get stagnant.
The floor drain has to be installed level and at the correct height so it sits slightly below the concrete floor. If it sits too high then water can’t drain into it. Make sure you take the measurement with the grate on because this adds height to most drains.

That’s basically it. As long as the drain is set properly into the garage floor and the pipes all run down hill, the drain will do it’s job.

Garage Floor Drain Codes

Almost every town and city has its own set of construction codes. If you’re building a new garage, call your local inspector to make sure the floor drain is installed according to requirements. There’s no sense doing all the work if in the end it’s not legal.

Some places require a filtration or catch basin oil separator to filter the water flowing out of the end of the drain pipe. This makes sure oil doesn’t drain into local streams or the sewer. They’ll also want to inspect the drain pipe to make sure it’s pitched properly.

Building codes are a collection of minimal requirements and generally all about safety. You can always build better than the building code require but never less. Every few years the building code is updated so make sure to check with your local building department before you start to ensure you don’t miss something. What’s required in one town may not be allowed in another so you should always verify codes with your local building department. Generally cities, suburbs and waterfront areas have stricter rules about drainage then more rural areas.

Generally a garage floor must slope to the exterior door so liquids flow outside. As for the drain,most codes dictate the pitch or the drain pipe and where the drain leads and not the actual drain itself. I haven’t been able to find a code that dictates using either a trench or bell style but you should verify code requirements yourself before starting any construction work.

How Deep Is A Garage Floor Drain?

Most garage floor drains are about 8 inch to 14 inches deep for the drain box.

Attached to the drain box is the drain pipe. Typically this is a PVC pipe that’s between 3 inch – 4 inch in diameter. Drain pipes can attach to the drain box in two ways, from the bottom or the side. If the pipe attaches the the side you won’t have to excavate as much. Simple secure the pipe and then pitch the pipe 1/8th to 1/2 an inch per lineal foot of pipe all the way to your drain out location.

If your pipe attaches to the bottom of the drain pipe then this requires a deeper excavation. You’ll generally attach a right angle fitting right to the bottom of the drain box and then run pipe at the same 1/8th to 1/2 inch per foot to the drain out. Because of the right angle fitting this adds another 6 inches or so of depth.

If you decide to add an additional P trap downstream from the box drain then you’ll need even more depth. This can add another foot to the job. The P-trap allows for another level of protection just like a kitchen or bathroom sink. I rarely use them in a garage floor drain but some homeowners like the option.

If you decide or are required to include an oil separator into the design of your garage floor drainage, then the size of the system needs to be included in your depth calculation. These can range from about 8 inch to over 2 foot depending on how big a separator tank you want.

When designing a system you need to take into account the height of point A and point B. If you live an a very flat area then you may not have the height for a complicated system. In cases like this, a simple side drain box leading right to the exterior is usually all that fits.

Where Does A Garage Floor Drain Go?

A garage floor drain leads to the outside just like all your other house drains.

Whatever type of garage floor drain you install, it must have an outlet leading water to a discharge point away from the house and garage. In some cases, a garage floor drain is connected directly to the sewer. But in most cases, the drain leads to the curb where water flows into the storm drain system.

In rural areas, the pipe typically leads somewhere on the property where it’s OK and safe to drain. Generally somewhere downhill where water can flow away from the house.

Garage floor drains should not flow into a septic system or well. If a well is used I like to make sure the drainage is far away from water sources so oil or chemicals can’t seep in. Drainage is something I take very seriously because it’s not always clean water that’s running into the drain pipe.

I recommend installing a system to catch any oil that spills onto the floor so you can dispose of it properly. If all that comes out of the drain pipe is water it’s less of a worry where the floor drain goes.