Trench Drainage vs French Drains
How to keep rain and stormwater away from critical infrastructure
When it comes to safeguarding your property, managing excess water is crucial. Whether from heavy rainfall or poor drainage, water can cause extensive damage to buildings, foundations, and landscapes, leading to costly repairs and long-term issues. Properties need effective water management systems to prevent damage and maintain their integrity. If you’re facing concerns about water accumulation on your property, understanding the right drainage solutions is essential.
This blog post will guide you through two of the most effective hardscaping solutions: trench drains and French drains. These systems are designed to manage water both at the surface and below ground, protecting your property from potential damage and enhancing safety. Before we dive into the specifics, let’s clarify some important terminology to ensure you have a solid understanding of how these drainage systems work.
Trench drain terminology
Here is some terminology you may come across as you learn more about trench drainage systems:
Debris chute
A debris chute is a sloped channel that allows debris to slide through easily into the trench below, preventing clogging and ensuring the system functions properly during installation.
Expansion joint
An expansion joint allows metal parts to expand without distortion, absorbing vibrations during events like earthquakes or ground settlement.
Gray cast iron
Gray cast iron, compliant with ASTM A-48, Class 35 or higher, is known for its corrosion resistance, good machinability, and durability. It experiences less shrinkage compared to other metals, making it ideal for high-quality trench drains.
Hardscape
Hardscape refers to any non-organic elements in a landscape, typically made of concrete, metal, glass, or stone. It includes structures like walkways, driveways, walls, and stairs that create usable spaces and often play a role in drainage.
Heavy-duty trench drains
These drains are designed to handle loads exceeding 16,000 lbs (H-20 load rating), making them suitable for heavy traffic areas.
Steel rebar
Steel rebar is used to reinforce concrete. In trench drains, it’s bent at 90 degrees to anchor the drains securely in surrounding concrete.
Seat form
A seat form is a piece of wood used during installation to adjust the trench drain’s position, ensuring it’s at the correct elevation relative to the trench form.
Trench forms
Trench forms are temporary wooden molds used to shape the concrete during trench drain construction.
Trench drain
A trench drain is a surface-level channel designed to rapidly evacuate water. Covered with grates to prevent debris from clogging the system, trench drains are commonly found in areas prone to water accumulation, such as parking lots, sidewalks, and loading docks.
Trench drains vs French drains
The primary difference between trench drains and French drains lies in how they handle water. Trench drains manage surface water, using gravity to direct it away, while French drains deal with subsurface water.
How trench drains work
Trench drains are designed to capture and redirect surface water away from your property or critical infrastructure. They are often lined with concrete and have a slight slope to facilitate water flow. Metal grates cover these trenches to prevent debris from clogging the system. Some even include a debris chute to conveniently collect any natural or man-made debris from entering the pipe and clogging the system. Trench drains are commonly used in areas like parking lots, high-traffic walkways, busy entrances, and pool decks to prevent water from pooling.
How French drains work
French drains consist of an underground perforated pipe covered with gravel or rock. Surface water filters through the gravel and into the pipe, which then directs it to a designated drainage area. These systems are typically installed around foundations or under basement floors to protect against water saturation. While effective, French drains require regular maintenance to check for debris, and usually need servicing every 10 years.
Installing French drainage
When installing French drainage, a slope of about 1% (or 1 inch per 10 feet) is enough for gravity to direct the water. To install a French drain, follow these steps:
- Choose a Location: Identify where excess water is pooling and where you want it directed. Ensure the water flows away from your property.
- Dig the Trench: Make it 9-12 inches wide and 18 inches deep.
- Line the Trench: Use water-permeable filter fabric or a weed barrier to prevent roots and dirt from contaminating the pipe.
- Add Gravel: Pour a 3-inch layer of gravel at the bottom for additional drainage.
- Install the Pipe: Consider adding a small grate at the surface level where the water pools the most. If you use PVC piping, drill holes at least every 6 inches along the entire length of the pipe. Place the pipe in the trench and test the flow to ensure it functions as expected.
- Cover with Gravel: Add another 3 inches of gravel on top and wrap any excess filter fabric around the pipe for extra protection.
- Backfill with Soil: Finish by backfilling with topsoil as desired.
Which direction do French drain holes face?
When installing piping for French drains, the holes should face down in gravel drainage systems because the water can more easily enter the pipe from the button. If they were at the top, the water level would need to reach the top of the pipe before it could get inside to wash away.
Installing trench drainage
Installing a trench drain follows a similar process, but instead of covering the pipe with gravel and fabric, you’ll cover it with a metal grate to keep debris out while allowing water to drain effectively.
How to choose grates for trench drainage
Cast iron trench grates are an excellent choice for everything from pedestrian areas to industrial loading docks. These grates are built to last and can withstand high loads while quickly removing excess water. With various designs available, from industrial to decorative, you can find grates that complement the aesthetics of your space.
Cast iron is built to last in any environment and even withstand high load capacities. Grates should be designed for durability, but design is an important part of people’s comfort and enjoyment of public spaces.
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