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3 Trench Drain Installation Tips You Need to Know

Since trench drains are part of the project’s foundation plan, they are literally the groundwork of their project. Entire projects can be “wounded” if the trench drain is dysfunctional.  The drain installation has much to do with how functional the drain will be.

And, drain installations can go horribly wrong.  Here are three trench drain installation tips to consider which may make your project run smoothly.

1. Orientate the channels correctly

All modular trench drain systems are composed of a series of connected channels. Pre-sloped drain systems use channels that run consecutively from shallow to deep.

Each pre-sloped channel has a number stamped or stuck to the side; the number indicates a specific invert/outlet depth.   There are also arrows on the side of each channel which point in the direction of the water flow, or rather, which point to the downstream (outlet) end. The channel with the largest number connects to your underground outlet pipe.

In preparation for the installation, place your channels next to the excavated trench, making sure the channels line up:

  • Numerically, from smallest to largest, and
  • With the arrows pointing toward the direction of flow

installing polycast, polycast installation, how to install sloped drain,

A common mistake by the novice installer is to ignore the flow direction indicator on the channel side.  This results in an apparent “miss-manufactured channel,” resulting in channel connections that are off by ¼” – ½”.  An easy way to ensure proper orientation is to always start by installing the deepest channel first and work upstream.  If you have the channels in order but are still having trouble, chances are that you have the arrows pointing in the wrong direction.  See Below.

installing pre-sloped drains, sloped trench drain install

2. Consider Time & Temperature

Modular trench drains made from HDPE and polyethylene trench drains are chemically resistant – meaning they won’t degrade under most common corrosive chemicals. These plastics, by their very nature, do have a higher coefficient of thermal expansion which can become as issue during installation.

Springtime is a big season for construction, but it’s also characterized by hot days and cool nights.   A common problem occurs when a long run of HDPE trench drain is installed in the heat of the day, when all the channels are warm and expanded.

dura slope install, installing dura slope, thermal expansion drains

In the cool of the evening, the total drain run will shrink as much as 6”.  This results in the complete run being put under tension and possible cracking at the weakest points (usually at the channel connections).  See below.  Avoid this problem by planning to set and install plastic trench drain in a single day or on days without a large temperature variable.

cracked channel drain, installing cracked drain

3. Prevent Channel Pinching

Some contractors and DIY homeowners unwittingly leave the grates off during installation. You don’t want to get your grates messy, after all.

However, concrete is dense and unforgiving when set.  Some light duty, plastic channel drain systems can pinch during installation under the wall pressure of the concrete.  The amount of inward movement can be imperceptible by sight, but the grates will not fit when you return to secure them into place.

channel drain problems, installation problem

Since trench grates are made to fit a specific channel, this simple mistake can ruin a project.

Try this instead:

  • Use plywood boards to maintain the channel’s shape during the concrete pour. Then remove and install grates once the concrete sets.
  • Wrap or tape grates and secure them in the trench before pouring concrete. You can go back and remove the protective cover once the concrete sets.
  • Some modular systems, such as Dura Slope by NDS, come with an installation cover which prevents the channel from getting filled with concrete and prevents pinching during the final concrete pour. (See Dura Slope Channels in Item 2.)