How to Install Floor Drains In Existing Garage Floors


You see floods don’t just take what you have. Floods take what you have and never give it back. Which is why institutions, governments and environmental agencies have stressed the need to protect your homes, workplaces, schools etc. from floods.

Five words. One sentence. That’s what they say in the commercials: “Install a proper drainage system.”

Amazingly, we have heeded to the warnings and have taken extra measures to do just that. Unfortunately, why humans are keen on protecting their homes and businesses from the ravaging storms and floods, we often neglect some things like home and office extensions.

Garages whether at home, workplace or as commercial centers all form part of these extensions. And they should be retrofitted too.

How to Install a Trench Drain In a Garage Floor

Getting the right slopes before digging a trench that stretches from your garage to the riser pipe where standing water or runoff is shepherded to be dumped at a safe area is vital to constructing a good floor drain.

Communities have codes in place that serve as guides to help you get the best results.

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Drains will never be optimized if your garage sits at the bottom of a pitch. If the garage floor has aged a bit, it may not meet the specifications for installing a floor drain.

Where any of this is the case, retrofitting works as a charm.  The existing floor is improved and modified to cope with the installation of trenches and drain pipes.

Things Needed for Retrofitting

  • Concrete saw
  • Jackhammer
  • Shovel
  • Mallet
  • Wheelbarrow
  • Concrete trowel
  • Straight edge
  • Plumb level
  • Re bar
  • Water
  • Tape measure
  • Chalk line
  • Fill sand
  • Premix concrete

Installing the Drain

Firstly, understand where your drain is going before driving your concrete saw into your garage floor. A convenient and efficient position is very important when picking a location. While scanning the floor, it is important you take the width of the trench into consideration.

In this case, when retrofitting an existing garage floor with a trench drain, 5-6 inches is the generally accepted width for the drain.

Let’s get you started then,

  • Take a measurement of the location on your garage floor where you want to have your trench placed.
  • Grab your chalk line, pull and snap two chalk lines to represent outside edges of your trench.
  • Next, you will need to pull that chalk line and snap again. This time around leave a 4 inches gap from either side of the edges of the trench lines from 2 These are where you start cutting from using your concrete saw.
  • The gap for the cut is often needed so that you can pour in concrete to hold your drain in tightly.
  • With your chalk lines already in place, use the concrete saw to cut along both outside chalk lines (the 4 inched line)
  • When done, break the concrete slab between the cut-lines using your jackhammer.
  • Remove the concrete debris using a shovel and a wheelbarrow from the trench. Dig between the space cut. The depth of the trench is usually 3 inches deeper than the channel drain, in the region of “8 inches”.
  • Collect your dug out soil using the wheelbarrow.
  • Fill up the trench with fill sand. Let the sand sit about 2 inches high from the base of the trench. Then level the sand.
  • Next, fix the drain sections. Some of them come with an instruction manual that shows you how it is done. Some require driving rods deep into the trench. Others, you just have to rest on top of the sand bed.
  • Adjust the top level of your channel/trench drain. Standard trench drains come with a “lip” on the interior top edges of the drain. These lips hold the grate in position with grate locks.
  • When installing the channel drain it should be flush with the garage floor. This means it the grate should never rise above the garage floor. Both should be on the same level else there is no way to capture runoffs.
  • Put the grate in place. Use the flat edge of a board to ensure it is leveled and sits well in the drain channel. Utilize a plumb level to give proper balance.
  • Channel drains are usually 5-6 inches wide. When placing them in the trench, you should have gaps. Fill those gaps with a wet concrete.
  • To go about this, use flexible material such as polyester or nylon to cover the floor drain, wet the premix concrete, then use it to fill up the sides of the channel drain. Fill and press down using the trowel, to ensure there are no pores for letting air in.
  • The wet concrete should be at the same level as the channel drain and the garage floor. Once done, allow the concrete and the drain sit for a period of about two weeks before driving over them.
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Slot Drains: An Alternative to Retrofitted Trench Drains

Although channel drains with grates are quite popular, a good alternative is the “Slot Drain System”.

Slot drains are a unique kind of drain system that come pre-installed and pre-sloped, great features that make retrofitting them in an existing garage very easy. Although they serve the same purpose as any linear or channel drain, Slot drains do not come with gratings, unlike trench drains.

How to Install/Retrofit Slot Drains In Your Garage

Understand where your drain is going before driving your concrete saw into your garage floor. A convenient and efficient position is very important when picking a location. While scanning the floor, it is important you take the width of the drain into consideration.

When installing a slot drain, the width is usually 24 inches in diameter.

  • Evaluate the length of the slot drain, dig a trench few inches deeper than the regular height of the slot drain and determine the width of the trench by considering the width of the drain itself with an added 4 inches on both sides.
  • Slot drains come pre-assembled. They can be coupled and uncoupled with makes them easy to install.
  • When placing them in the trench, it is recommended you rest broken concrete or filler sand on the bed of the trench. This helps the slot drain sit properly.
  • In addition to the previous point, sidewalls that then to bend inwards (bowing of walls) should be reinforced to ensure the slot drains or any kind of channel drain function properly.
  • Once the slot drain has been set properly in place, take your time to inspect if it is on the same level as your garage floor. If not, make the necessary adjustment. This is done to prevent any form of accidents or unevenness.
  • If rebars are driven down to hold the slot drains, fill up the spaces with wet concrete between the rebars and the slot drain to hold them in place.
  • While doing this, use some a tape or a protective product that can protect the opening of the slot drain, preventing any form of concrete mixtures from falling inside.
  • Allow the concrete to harden before removing any protective material used to secure the slot drain.
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NOTE: Retrieving fallen items in a slot drain is difficult since there are no gratings at the mouth of the drain and they are slimmer in width than a trench drain. Still, they make a good alternative to the trench drain.

Things to Consider Before Retrofitting Your Garage for Drain Installation

Preparing Concrete Slab and Retrofitting

Installations of floor drains are usually done when constructing your garage. They are best done before pour your slab.

Drains installed in garages must function properly if they are expected to collect water. The runoff is ferried away from the house. In retrofitting, the concrete slab in the garage must be well pitched if you are considering tearing it up and installing a drain beneath it. When retrofitting an existing garage, parts of the concrete slab is sliced off, and removed completely. Trenches are dug to accommodate the pipes. This sometimes can be a difficult process if not carefully done.

The Drain Systems

A typical drainage system may or may not have grates that suck in water. Usually they are connected to riser pipes. These fixtures are connected to the underlying pipes that lead away from the garage to a safer place. The grate (trench drains in this case), usually metal or plastic sits on the same level as the garage floor. The drain pipes are buried hidden under the soil.

A well designed drainage system is one that effectively does the task of ferrying runoffs, standing water away from the garage. Grates in trench drains are often selected based on size. If more water snakes its way into your garage, the number of drain grates to be use could increase.

Channel Drains

Sometimes called linear drains or trench drains, are known to handle worse runoffs than the conventional drainage system. They can handle large volume of water. They have been tipped as favorites among garage owners. Often times they are installed across driveways away from garages.

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Garages that have their driveways sloped toward the garage and the garage floor from the back of the garage sloped in the same direction makes collecting runoffs easy when they meet at the drench drain just outside the garage door.

If trench drains are to be installed, it involves cutting bits of your concrete slabs, digging a trench, installing the drain channel, and holding it in place using wet concrete. And finally sealing up trenches away from the garage that contain drain pipes with soil.

Building Regulations

Communities learn to exist together because they live by guided by codes and regulations.

Statutes must be upheld to prevent any form of abuse. And these statutes blankets how the environment should be protected.

That said, before installing a floor drain in your existing garage consult your local authorities. Some communities frown at the idea because they fear it could harm the community in some way especially when your house dumps chemicals that could possibly degrade the environment. Others have guidelines that have been carefully laid down for garage owners to follow if they plan to install a floor drains. Dig out this details before making any moves.

Flood Disasters: Their Effects on Your Garage

Climate change continues to wreak havoc on lands and properties that are vulnerable sparing almost nothing on its path.

According to Organization for Economic Cooperation and Development, a standing figure of over 40 billion dollars is lost to flood. And that include Sam’s losses too.

If we put aside our cavalier-attitude and give a little more attention to worrying damages caused by runoffs, poor drainage, floods then we can start winning significantly.

  • Floods cause displacement. This in turn leads to property loss.
  • If your garage is constantly being attacked by stagnant water from rainfalls it risks getting winded up.
  • Flood makes your garage unsafe for work. Slips are very common in poorly drained areas.

Many garage owners often make a horrible mistake of building a very decent garage and end up not installing a floor drain. Not even a conventional drain to check the problem of standing water. And usually they feel sorry afterwards.

Garages without a preinstalled floor drain will always accumulate runoffs from heavy downpours because drains are absent to collect them.

They will look messier and unsafe for work. When floor drains are installed while constructing garages, water issue will be cut down especially in areas that are seriously affected by heavy rainfall. But when this is omitted, it is a recipe for disaster.

Are there options then? Yes, fortunately.

This is where retrofitting comes in. Basically, this involves cutting your concrete slab and installing a drain.  Although this is herculean, very tasking, but it is achievable.