Outdoor Trench Drain Systems

10 outdoor trench drain system considerations


So you’re buying or planning for  a new outdoor  trench drain system. It can be a daunting process. There are so many manufactures to choose from, NDS, Josam, ACO, Swiftdrain. There are different grate materials and channel materials. There are some that cost just a few hundred dollars online and some in the thousands. So where to begin? We break down the 10 main considerations when selecting the right trench drain. Whether it's for your home, a commercial application, a parking lot or an airport checklist applies for trench drains on a general scale and can be applied for every project, big or small.




  • Load Bearing
  • Site Requirements
  • User Requirements
  • Weather
  • Slope
  • Expected Inflow
  • Outlet
  • Catch Basin
  • Grate Material
  • Channel Material


Heavy Duty Pre Cast Concrete materials can be used for outdoor drainage projects. Fiber reinforced and polymer concrete drains come pre sloped, have galvanized steel frames and a variety of grate options. Enhanced concrete doesn't degrade when subjected to high and low temperatures, freeze-thaw cycles, acids, and UV rays. These polymer composites are a cost effective and less labor intensive alternative to pour in place, hand formed systems.


Outdoor trench drains should have the appropriate grate style for external site and user conditions. Grates can be locking for added security. Grates slot style can also be heel proof or ADA for pedestrians. Grate material choice will also determine how well it holds up in different climates and under different chemicals. Expected water flow will determine the width of the grate. Generally speaking, 6" - 14" wide is suitable for most exterior outdoor trench drain applications.


When choosing the right outdoor trench drain one of the most important factors to consider is load rating or how much weight is expected to be applied on the drain.


Load Rating is classified into 5 major categories:

Class A
Class B
Class C
Class D
Class E

The load rating will assist in determining the appropriate grate material, whether it be cast iron, ductile iron, galvanized steel or polymer. Trench drains can also be coupled with frames to increase the load capacity.


Site requirements consist of things like Slot Style. Does the drain need to be ADA or heel proof? Do the grates need to be coated because of the use of caustic chemicals, snow melt, acids or extreme temperatures. Stainless steel is generally used in areas with high temperature fluctuations and caustic chemicals. It makes the ideal choice for brewery applications. Galvinized steel is suitable for outdoor weather conditions as it’s less likely to rust compared to cast iron.


User Requirenments consist of features particular to an application. For example in areas where theft is an issue or airports most grates are bolted for extra security. User requirements can also be customized such as large trench depths and custom slope designs.


Weather plays a role when selecting the right grate and channel material. Hdpe is a good channel choice as it holds up well against freeze and thaw cycles. Galvinized steel is a good grate choice as it doesn’t oxidize in cold weather conditions or with snow melt.


Slope is the pitch of the trench drain run. Common slopes range from no slope, or neutral slope to .5% to 2%.. Slopes can also be customozied where some sections are more aggressive than other areas. The NDS Dura Slope has a customizable sloped design with a .5% built in slope. For most outdoor trench drain applications, .5% is the go to pitch.




There are two main installation methods for outdoor trench drain systems. The hanging method and rebar method. The hanging method uses wood planks to build a form where the trench channel hangs from. The concrete is poured around the channel while it hangs. Think of a person doing a pull up. The drain hangs from the wood planks, which is fastened to the top of the drain and is suspended. The rebar method uses 4 rebar every section (3 or 4 feet). The rebar is fastened or placed in its anchor and the concrete is poured around the stake which is attached to the channel and drilled into the surrounding concrete. Both installation methods are suitable for outdoor trench drains.


Concrete encasement depends on the load rating one wants to achieve. Generally speaking, 4" around and 4" below the drain is suitable for pedestrian traffic or class A. An encasement of 6" around and 6" below is suitable for medium duty traffic, class B, C and D. And for the heaviest of loads, an encasement of 6", 8" and up is used for Class E and F H-20 and better. Concrete encasements are important for outdoor trench drains as the force applied to the grate is distributed to the encasement through the channel form.


Expected inflow is how much liquid and what flow rates are expected to enter the drain. This will assist in choosing the width and pipe outlet size. For most applications, 6” wide, 8” wide and 12” wide can handle most weather climates and expected water inflow.


Outlets are the end piece in which connect to the pipe outlet. The outlet acts as adaptor for the end of the trench drain run. Outlets can be at the bottom of the drain (bottom outlets) or at the side of the drain (side outlet) Outlets range in sizes 3” 4” 5” 6” 7” 8” and above.


Catch basins are traps used along the trench drain to collect debris and sediements. Catch basins can be inline or square. Catch basins can also have strainers and other sediement filterstion devices.


Grate Material consists of cast iron, galvanized steel, ductile iron, polymer and stainless steel. Grate material is chosen by considering the expected weight load and site conditions. Polymer is suitable for class A and B. Cast Iron, ductile iron and steel is good for A, B, C, D, E and F. The thickness of the grates increase its load rating as it adds more tensile strength. Grate materials like stainless steel is good for areas with caustic chemicals and high and low tempratures.


Channel Material choices consist of stainless steel, polymer , fiber reinforced concrete and polymer concrete. Channel materials come into play for areas with high and low temperatures, chemicals and load strength. Pre sloped channels are a cost effective and accurate alternative to cast in place methods. Pre sloped trench drains come in fiber reinforced concrete, polymer and polymer concrete materials. A 1% slope should be used for the pipe outlet.




Pre cast trench drain systems used to be the go to standard. Over the years many manufacturers have introduced pre sloped polymer based channels. The channels are easy to ship, install and maneuver. They are extremely light weight and easy to install. Each channels are numbered and connect together with slip joints like lego pieces. Polymer channels are extremely strong and can achieve load ratings A-F suitable for most applications. These systems provide modular design flexibility, decreases error, requires less installation time and has lower installed cost when compared to conventional cast in place trench drains.


Polymer and polymer concrete trench drains are well suited for a variety of outdoor trench drain use cases.
Polymer and polymer concrete outdoor trench drains are made of highly durable materials. Channels have greater load strength, chemical resistance, weather resistance comparative to its Portland cement counterpart. Polymer concrete holds up well against weather fluctuations, anti freeze, and UV rays.
Most manufacturers offer trench drain systems suitable for outdoor and exterior drainage. Polymer and polymer concrete offer a competitive and economical advantage over Portland cement cast in place systems.




Water build up outside of a garage can seep into the basement. Dealing with surface water build up is critical to mainting the integrity of any structure or parking area. Often its not where the water begins yet where it flows to that causes a concern. Water buildup infront of a driveway can often seep into a basement and cause damage over time. Its best to plan and install a trench drain first, rather than deal with the headache water damage in the future.




Learn more about outdoor trench drain product offerings here.