Common French Drain Mistakes
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Common French Drain Mistakes & How to Avoid Them
Installing a French drain can be a complex process, and if not done correctly, it can lead to costly repairs and frustration. It’s important to work with experienced professionals who understand the proper techniques and materials needed for a successful installation. They can also help you avoid the most common mistakes and ensure that your drainage system is built to last.
1. Not Calling Before You Dig
Before beginning any digging or trenching project, it’s important to call 811, the national call-before-you-dig hotline, to have the underground utility lines marked. This service is free, and it’s the law in most states. The markings will help ensure that you don’t accidentally dig into a utility line and cause a potentially dangerous situation, such as a gas leak or electrical shock. It’s always better to be safe than sorry, and taking this simple step can save you time, money, and potentially even your life.
2. Using the Wrong Type of Drain Rock
The size and quality of the drainage rock used is essential for the proper functioning of a French drain system. The rock should be clean, free of debris and sediment, and made of a hard, durable material like granite or basalt. The ideal size for the rock is between ¾ and 2 inches in diameter, as this allows for optimal permeability and water flow. If the rock is too small, it can easily become clogged with sediment and debris, while larger rocks can create voids that water can’t flow through. Using the right drainage rock is critical for preventing clogs and ensuring that your French drain system works effectively for years to come.
- Use Natural 1-1/2" round rock for best drainage. Washed rock is ideal.
- Avoid small pea gravel as the spaces in between stone is smaller minimizing flow rates.
- Avoid Crushed Rock (minus) that compacts and has "fines" that will clog pipe inlets.
3. Not Lining the Trench with Drainage Fabric
Without the drainage fabric, the soil and debris can mix with the drain rock, causing the system to become clogged and ineffective. A non-woven geotextile drainage fabric provides a barrier between the soil and the drain rock, allowing for proper drainage while also preventing the system from becoming clogged over time. It’s an important step that shouldn’t be overlooked during French drain installation.
- Correctly built French drains utilize a non-woven geotextile fabric ranging from 4 oz to 6 oz in weight
- High quality drainage fabric can last for decades without issue
- Avoid using socked wrapped perforated pipe alone without drainage fabric as it will easily clog with dirt/soil.
4. Selecting the Wrong type of Landscape Fabric (use non-woven)
Select the correct type landscape fabric that will properly drain sub-surface water is key to installing a functional and long lasting French Drain.
Non-woven fabric is a popular choice for French drains because of its ability to allow water to pass through while keeping soil and debris out. Its permeability is achieved through the use of small, evenly distributed holes or pores, which are created during the manufacturing process. Additionally, non-woven fabric is typically more durable and tear-resistant than woven fabric, making it ideal for use in construction and landscaping projects.
5. Placing Excavated Soil Back into the Trench
Adding soil or clay back into the trench after installing a drain system should be avoided. This is because the primary purpose of a French drain is to facilitate the movement of water through the soil and into the drain, where it can be safely diverted away from the foundation or other structures. When soil or clay is added back into the trench, it can impede the flow of water, clog the drain, and reduce the capacity of the French drain over time. It is important to use clean and properly sized drainage rock for your drain fill material, along with a non-woven geotextile fabric to act as a soil separator and prevent dirt and debris from mixing with the rock fill.
6. Lack of Positive Slope for the Drain
Proper slope or gradient is important for the drainage pipe to work effectively. The pipe should be installed with a minimum slope of 1% (1/8 inch per foot) to allow water to flow freely and prevent standing water from accumulating inside the pipe. If the slope is not sufficient, water can collect and create blockages, reducing the efficiency of the French drain system.
7. Gravel Only drain without a Drain-pipe
A French drain is a drainage system that typically consists of a trench filled with gravel or rock and a perforated pipe that is installed to collect and move excess water away from the foundation of a building or property.
Using only gravel or rock without a drain-pipe can be a mistake because the water will not be moved away from the area effectively and will simply saturate the surrounding soil, leading to potential damage.
The drain-pipe is a critical component that carries the water collected by the rock or gravel away from the area, preventing it from saturating the soil and causing damage to the foundation or property. Without the drain-pipe, the water will remain in the area, defeating the purpose of the French drain and potentially causing more problems.
Having a drain pipe, most commonly a 4″ or 6″ perforated pipe surrounded by round drain rock provides the capacity to move this water away from structures and prevent pooling.