A trench drain can be an expensive item to install. First you have to invest time and energy into trying to solve a drainage problem. Then, there is the cost of the drain itself: channel, top grating and shipping costs.
Next, there is an expense associated with the installation. Maybe you use a contractor. Maybe you do it yourself and end up with a sore back or smashed thumb. You have concrete and other supply costs, as well. It all adds up. If it’s a home project, there is some personal frustration associated with the whole affair. So, in the end you want the drain to actually solve the problem.
Shortcuts and misunderstanding the breadth of the problem lead to a failed trench drain. Usually, I am brought in to consult with the project owner after the failed drain is discovered. I have seen enough of these to lump the failures into three categories.
There is a misconception that you don’t need to use concrete when installing a channel drain. Put this out of your mind. In most cases, you NEED to encase your trench drain in an envelope of concrete.
The only situation where you don’t need to pour concrete is in a paver patio that will never see vehicle traffic.
The example to the left shows a polymer concrete drain installed in a paver driveway. Polymer concrete has a high compressive strength but is brittle and easily breaks when dropped or put into a dynamic force situation.
The abutting paving stones could have settled a bit in this drive. The top edge of the trench drain became exposed to the dynamic forces of the car wheel, which broke the channel walls at the base of the drain. The contraction and expansion of the stones freezing and thawing may also have played a role in the disintegration of the drain.
Originally, a modular trench drain was sold as a “form” which was used to when forming a drain out of concrete. The drain body wasn’t the strength of the system, it was the shape. When a drain is encased in concrete, the concrete takes the shape of the drain and becomes the strength of the drain. Often, suppliers will specify a thickness of concrete needed to achieve a specific drain load classification. Four inches are used in small automobile traffic. Eight inches for heavier loads.
A drain can’t merely be sitting adjacent to the concrete.
The concrete must encase the body of the channel intimately. In the example above, the client poured the concrete allowing a gap for the trench drain to be grouted in after the fact. Because there was no support below or from the sides of the channel, the plastic channel body and grates were easily crushed under the weight of an automobile. If the entire drain was supported by concrete, the weight load of the car would have been transferred to the concrete and the drain would still be intact.
“Can I use asphalt to install my drain?”
Generally, I would say “No”. I have seen situations where the majority of the drain was encased in concrete, but the top surface adjoining the drain was tamped with asphalt. That is doable if the contractor takes care not to crush the drain during asphalt compaction, but that is not a risk I’d like to promote.
Encasing the entire drain in concrete is preferred – and easier for the installer. The asphalt can be compacted next to the concrete. If there is an aversion to the contrast between the light grey concrete and the black asphalt, one could always seal coat the concrete to make it blend in. If not, you may end up with a drain that looks like the photo below.
Improper Drain Selection
You can install a product beautifully, but if you install the wrong drain you are not going to have a good time. Such is the case when you put a plastic drain in an area that sees fork truck traffic (below).
For applications where a drain is going to see repeated automobile, delivery truck or fork truck traffic, a heavier duty drain is required.
I recommend drain bodies made from HDPE or polymer concrete with grating recesses that are supported by embedment concrete (i.e. the grate is wider than the channel opening). Channel bodies capped with a metal frame and heavy duty grating are more preferable.
Some drains are meant to be used in light duty, residential applications only. Those little plastic drains you buy at the big box stores (Lowes, Home Depot, and Menard’s) are meant for use in a patio or maybe a driveway with little automobile traffic. Often, the channels are made from extruded cellular PVC and the structural support on which the grating rests is made entirely of plastic. The light duty construction of these channels will have a tendency to break under heavy loads or due to the freeze-thaw episodes seen in the winters up north.
Another improper drain selection situation is when you install a drain that will see a larger amount of water than it can handle.
The drain can be installed perfectly, but if the drain is overrun with a deluge of water, it is not serving its purpose.
A Pipe Size Calculation is nice to do prior to selecting your drain just to double check that you have a drain that can handle the water flow anticipated.
Improper Grating Selection
An incorrect grating selection can also lead to trench drain problems. The most common problems arise when the grating either has:
- Insufficient load rating or
- Insufficient chemical resistance
Load rating problems are common.
The cheaper grates generally have a lower load class. Class A load gratings, for pedestrian applications, are sometimes used where automobile traffic is frequent thus leading to grating failure. I’ve seen contractors or engineers choose a lower class grating because it met the budget of the project. Later, of course, the owner of the project would have to replace the grates anyway.
This is the case for the example to the left. A winery had stainless steel slotted grates installed that had Class A loading. The application actually needed a grating with a much higher load rating. As stainless steel is expensive enough, the project settled on the cheaper stainless grates only to come back later looking to replace the grates with the appropriate stainless steel product. Money could have been saved by making this decision during the initial installation.
Insufficient chemical resistance is also a common example of an improper grating selection.
We don’t always think about the quality of the water or environment that the drain is going into. Sometimes it just slips our mind. Additionally, we may want to ignore the chance that the drain is in an aggressive environment because that will force us to consider more expensive, chemical resistant grating options.
Consider those folks that live near the sea coasts of Florida, California or Washington. The salt water atmosphere plays havoc on cast iron and galvanized steel. Eventually, trench covers corrode and need replacing. For coastal environments, it is wise to consider a stainless steel, HDPE or fiberglass grate when possible.
Likewise, in dog kennel applications, galvanized steel grating eventually corrodes from the dog urine and harsh cleaning chemicals used. This leads to a premature replacement of the grates. For non-profit organizations, who are always looking to cut costs, it is tempting to use a low cost galvanized steel grate for the kennel application. It would be better in the long run to use a stainless steel or perforated HDPE grating so to avoid expenses later.
Much of these problems can be summed up to poor workmanship. Here are a couple take-aways:
- Make sure the contractor installing your drain has experience doing so.
- Discuss the type of traffic, environment and aesthetic requirements for the drain system.
- Discuss grate options with your contractor and communicate your expectations of the grate material and pattern.