When I bought my house, the builder said that my concrete garage floor was sloped, so any water runs directly outside.
I wanted to know if I could add a garage floor drain to an existing concrete floor.
You can install a floor drain in a new or existing garage floor, even if the floor is just a concrete slab. You can attach the drain to your sewer line or direct the flow to runoff outside. If water is pooling in your garage, a floor drain will help prevent concrete damage to your floor and foundation.
There are some additional steps and considerations you need to take before you start to dig.
Let’s talk about them now.
Check Permit Requirements
Before ripping up your garage floor to install a trench drain, find out if your municipality allows it.
Start by checking with your local authorities to find the building codes, permit regulations, and inspection requirements. Don’t do anything without knowing if a garage floor drain is allowed and if you have any additional requirements.
This is especially true if you intend to connect your garage floor drain to the sewer lines.
In many municipalities, this is strictly prohibited. Even if it’s permitted, it’s only for water only. Any hazardous materials in the garage (including gasoline and oil) must be kept from entering the sewer line.
Specialized equipment can help protect the water supply from hazardous chemicals. You’ll need to install it if there’s a risk of oil or other chemicals going down the drain.
Some municipalities will require this for all garage floor drains, no matter what.
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 key takeaway is that it’s easier to reach out to your local building code office before making changes. Otherwise, you may have to rip out your new floor drain.
Do your research beforehand!
Find the Low Point on Your Garage Floor
Floors designed with a drain are graded, so the drain is at the lowest point. This allows the floors to drain on their own without water pooling.
Since you don’t know the exact grading of an existing concrete garage floor, you need to find where the water pools.
You probably know where some common spots are, but it’s worth investing the time to find them all.
Using my garden hose, I sprayed my garage floor with water and let it settle. You don’t need a lot of water, just enough to form puddles.
I found water pooling in several areas on my garage floor I wasn’t even aware of.
Next, I took a permanent marker and drew outlines around the edges of the puddles. After repeating this a few times, I knew exactly where to place my floor drain.
You don’t need a drain if water doesn’t pool on your garage floor. Use a garage floor squeegee to direct the water towards the garage doors, and let gravity take care of the rest.
Depending on your garage layout, making a short channel in the concrete floor and a longer trench in the soil outside might be easier.
Even if it’s not the most direct route, digging dirt is much easier than breaking up concrete.
Check Where You Are Digging
Check the location of existing water lines or other utilities in your concrete floor. 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. You can do that in the United States and Canada by simply dialing 811.
If you don’t take precautions and hit a utility line, you are legally and financially responsible for any damages.
Always check before any excavation.
Tools Needed to Install a Garage Floor Drain
Once you have planned the new line and gotten permits, it’s time to get to work.
- Eye protection
- Work gloves
- Pickax or mattock
- Garden hose
- Jackhammer (optional)
- Pry bar
Installing a garage floor drain in an existing concrete floor requires using a jackhammer or concrete saw (or both). Concrete work is complex, and cheap tools are only up to the job.
You can usually rent professional-quality tools at your local Lowe’s or Home Depot.
Dig the Drain Trench
You’ll need to cut a trench in the slab where the garage drain will be to where it exits your home, just beyond your garage door. This trench should be about twice as wide as the pipe and deep enough to accommodate the pipe plus the drain fixture itself.
It’s essential to have the drain pipe slope downward so water will flow through it naturally.
I recommend using a concrete saw to help make straight edges on the trench. Then, you can use a sledgehammer and prybar to break up and remove the concrete in the middle.
One common mistake DIY’ers make is forgetting to make the trench deep enough to allow for the proper pitch and also to accommodate a p-trap at the drain.
The p-trap (also called a u-bend) is a bend in the pipe shaped like a ‘U.’ It will always hold enough water to seal the pipe, preventing sewer gas from leaking into your garage.
Next, dig a connecting trench drain outside as well.
The exterior trench drain should start at the pipe’s exit at the edge of your concrete floor, continuing to the final drainage point. If your garage has an apron, the drain should be placed in front of the apron, immediately after your garage threshold.
Lay the Pipe
Once all the trench drains are dug, it’s time to lay pipe.
Note: The pipe MUST slope downward from the floor drain’s inlet to the endpoint outside. This is so that liquids flow through the pipe to the main drainage system outside.
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 drain pipe is laid and you are happy with the slope, it’s time to fill the hole with self-leveling concrete. This will allow you to refinish your garage floor, so it’s nice and smooth.
Before you pour the concrete, cover the drain temporarily to keep concrete out of your new garage floor drain.
Mix the concrete a little at a time and pour it into 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.
Once the concrete is dry, you can seal the floor or cover it with an epoxy coating to help protect it.
Use a rake or shovel to place the soil back into the trench you dug to cover the exterior trench.
Once the trenches are covered, remove the covering over the drain hole in the garage. Install the drain cover to stop any debris from getting into the pipe, and your new garage floor drain is good to go.