When I bought my house, the builder made a point of saying that the garage was sloped in such a way that it would run all the water outside.
It doesn’t.
So I started looking at whether you could add a floor drain to an existing garage floor.
Can you put a floor drain in an existing garage? Yes, even if the floor is just a concrete slab. The drain can be attached to an existing sewer line or just flow to a runoff outside. If water is pooling in your garage, a floor drain can help you remove the mess before it spreads into your house.
There are some additional steps and considerations you need to take before you start to dig. Let’s talk about them now.
Check if you need a permit
Before you start ripping up your garage floor to install a drain, you need to find out if your municipality allows it.
Start by checking with your local building authorities to find out the building codes, permit regulations, and inspection requirements. Don’t do anything else until you are sure the drain is allowed, and you understand the other legal requirements.
I wrote an article discussing whether you needed a permit to drywall your garage. It’s a different project, but a lot of the information still applies, so check it out.
The bottom line is that it’s easier to reach out to your local building code office before you start making changes. Otherwise, you may have to undo all the improvements you made.
Put It on Paper
Once you have the green light to proceed, start by drawing up a plan.
Garage floors that come with a drain are graded with the drain at the lowest point. These floors drain on their own with no pooling.
To retrofit a drain to your garage floor, identify the spot where water pools naturally. This is where you will locate the drain.
If your garage is sloped in such a way that it forces the water to run out under the door, then you probably get by without a drain. Just squeegee the water towards the door and gravity should take care of the rest.
Once you have the low-point in the floor picked out, determine if you want to tie the new drain into the existing sewer line. Note: In many municipalities, this isn’t allowed. Do your research beforehand!
If you plan on tying your floor drain into the sewer lines, be aware it’s for water only.
Any hazardous materials in the garage (including gasoline and oil) must be kept from entering the sewer line.
Equipment is available to protect the water supply from hazardous chemicals – install it if you think you might rinse oil or other chemicals down the drain. Some jurisdictions require this in a garage drain, no matter what.
Depending on your layout, it might be easier to make a short trench in the concrete floor and a longer trench in the soil outside.
Even if it’s not the most direct route, digging dirt is a lot easier than breaking up concrete.
Check Where You Are Digging
Check the location of any existing water lines or other utilities in the slab where you will be working. The last thing you want is extra water in your garage from a broken water line.
Before you dig, you will need to call to have the utility companies mark the location of existing underground lines. In the United States and Canada, you can do that by simply dialing 811.
If you don’t call 811 and hit a utility line, you are legally and financially responsible for any damages. You should always call 811 before any kind of excavation.
Get the Right Tools
Once you have planned the new line and gotten permits, it’s time to get to work.
Installing a floor drain in a garage requires the use of a jackhammer or concrete saw (or both). Concrete work is difficult, and cheap tools aren’t really up to the job.
Your best bet is to rent the tools you need then send them back when you’re done.
Digging the Drain Trench
You’ll need to cut a trench in the slab from the spot where the drain will be to where it exits the building. The trench should be about twice as wide as the pipe and deep enough to accommodate the pipe plus the drain fixture itself, plus a little more so you can slope the pipe downward.
I recommend using a concrete saw. It will make straight edges on the trench. You’ll still have to break the middle of the trench out with another tool, though.
If you’ve cut a deep enough trench, you should be able to split the middle piece into smaller sections and life them out with a crowbar. If not, you may need to use a sledgehammer or jackhammer to break up the concrete.
It’s important to make the trench deep enough at the beginning to accommodate a p-trap at the drain!
The p-trap (also called a u-bend) is a bend in the pipe that is shaped like a U. It will always hold enough water to keep the pipe sealed and prevent sewer gas from leaking into your garage.
Once you have a trench inside, dig a connecting trench outside as well. The outside trench should start at the edge of the slab where the pipe will exit and continue to the final drainage point.
Lay the Pipe
Once all the trenches are dug, it’s time to lay pipe.
It’s important to keep the pipe sloping downward from your garage to the endpoint.
Sewer drains are gravity flow affairs. You need the slope to make the water keep moving from the garage, through the pipe, to the main drain line. If necessary, shim the upper end of the pipe to force it to slope.
Consider installing a clean-out in the pipe just after it exits the slab. You may never need it, but it’s nice to have if anything ever goes wrong with the pipe.
Refinish the Concrete Floor
Once your pipe is laid, and you are happy with the slope, it’s time to fill up the hole with self-leveling concrete so it’s nice and smooth.
Before you pour the concrete, be sure to cover the drain in some way (can, wood, or another piece of pipe) to keep concrete out of your new drain.
Mix the concrete a little at a time and pour it in the trench. Let it slump down and smooth the new concrete with a trowel. Use a trowel to smooth the new concrete after you pour it.
Staining the concrete or installing flooring can conceal the marks of the trench if you are concerned about appearances.
Outside, it’s much easier to hide the trench. Simply use a rake or shovel to place the soil back into the trench you dug. It may stand a little bit taller than the soil around it, but it will pack down with time.
Once the trenches are covered, remove the covering over the drain hole in the garage. Install the drain cover, and your new drain is good to go.
