Water management is essential in most construction. Water accumulation in landscaped areas or around retaining walls or basements can lead to more problems than a temporary wetness. Poor drainage will cause pressure build-up, waterlogging, and damage to the construction and waterproofing of the structure.
The drainage cell was developed to solve the above problems.
Drainage cells are modular systems that are three-dimensional and create open drainage behind or beneath a surface. Rather than letting excess water be trapped by the soil or fill, the system allows the water a means to move to a drainage outlet.
Due to drainage cells being modular, lightweight, and available in numerous configurations, they are found in a great variety of building and landscaping applications such as retaining walls, drainage in basements, and green roofs and in planter boxes and podiums.
What does drainage cell mean?
Drainage cells are modular drainage systems that allow construction of voids that are continuous in drainage.
Typically, drainage cells are three-dimensional structures of plastic that have a lot of openings that are interconnected. After the drainage systems are assembled, the openings will remain unfilled and will be a drainage layer. Depending on the use, the drainage cells can be positioned horizontally or vertically.
In most drainage cell systems, there is a layer of geofabric or geotextile. The fabric acts as a filter and helps keep soil out of the drainage space. This helps make sure soil particles do not enter the drain space and cause a blockage.
Different products have different designs, some for different flows, or for different levels of soil compression, or even for different methods of installation. Therefore, consider the drainage, the compression strength, and the measurements of the product before choosing a specific product.
How Does a Drainage Cell Work?
It is a simple concept.
Picture soil with a wall on one end or a landscaped area on the other. If soil has no drain, and no drainage path, the soil can become saturated and can even overflow.
A drainage cell allows soil to build up without flooding. Water fills the drainage cell and flows through the cell to a drainage outlet.
In a vertical design, the drainage cell can be placed against a wall. Water will enter the drainage cell and flow down toward the outlet.
In a horizontal design, the cell has the same function under a planter or a garden. The drainage cell transfers water from the soil to the outlet.
The cell does not soak up water. The cell allows water to flow.
Where Are Drainage Cells Used?
Because of all the functions a drainage cell can perform it is a very desirable product.
Construction drainage principles can even be applied in multiple areas of construction.
Green Roofs and Roof Gardens
Rainwater can be absorbed by the vegetation and the growing medium of a green roof. Roof systems can even help the growing medium retain water. However, this can hold back too much water.
To solve this, a drainage cell can be installed beneath the growing medium to help create a pathway for excess water to be drained. Additionally, drainage cells help separate the landscaping and the waterproofed roof system.
This makes drainage cells ideal for all types of green roofs and green roof gardens.
Drainage components of a green roof must work with a green roof system. The drainage cell must also consider the loading of the roof system and the drainage & outlet design.
Planter Boxes
Another very popular example of drainage system components in construction. The main effect of insufficient drainage in a planter box is the creation of a saturated soil around the plants. This can potentially harm the plants and support structures as well.
To prevent this a drainage cell can be installed to create a drainage void. To prevent the soil from acting like a sedimentation tank, a geotextile filter can be placed over the drainage cell.
This can especially be beneficial to elevated planter boxes.
Retaining Walls
Water behind a retaining wall must be addressed.
If water behind the wall can’t drain, it can lead to increased pressure on the wall. If you want to prevent this, you should consider installing a drainage cell vertically.
Drainage cells are frequently integrated into the drainage design of walls and abutments.
Drainage cells and systems should be designed with consideration of the wall design, the existing and anticipated ground water, the soil, and the local construction practices.
Basement walls
While basements experience nearly the same issues as above-ground walls, inadequate drainage systems can result in far greater problems.
Water collecting around structures that are completely underground exerts pressure on the wall and can create issues related to moisture. A drainage cell can be integrated in the below ground drainage system to create a drainage pathway to the soil surrounding the wall.
In most systems, the drainage cell layer conveys water to a perimeter drain, or other collection systems.
One important thing to note is that drainage cells are not the same as waterproofing.
Waterproofing is designed to keep water from penetrating the structure. Drainage manages the water that reaches the drainage layer. In a high-performance basement system drainage cells and waterproofing are both used in conjunction with the other, to achieve the desired result.
Podiums and landscaped decks
Podium decks often combine structural slabs with landscaping, paving, and drainage layers. Because the available build up depth can be limited, a dedicated drainage layer is often used. To create drainage voids beneath landscaped areas, drainage cells are appropriate and can maintain a relatively lightweight system.
What product is appropriate will be determined by the type of loads expected and the construction build up, particularly paving, planters and other heavy elements.
Main Advantages of Drainage Cells
Benefits will vary by product and design, however there are a number of reasons drainage cells are preferred in modern construction.
Effective Space Usage
The construction of a drainage cell allows a void to be defined without the need to fill a drainage zone completely with aggregate.
This is particularly helpful in construction with a limited depth such is the case with roof top gardens, planter boxes and landscape podiums.
Bulk Drainage Material Substitute
Compared with large amounts of aggregate, drainage cells are a more lightweight construction material.
This may help in the transportation and handling, particularly in cases where drainage must be carefully considered due to the structural loading.
Permeable and Continuous Drainage System
The system, when integrated with the appropriate outlet and filtering elements, can help facilitate the movement of water from drainage to collection and prevent the water from ponding in the drainage layer.
Waterproofing Protection
The drainage layer may provide a protection system to a waterproofing membrane.
Frequently Asked Questions
Can drainage cells be used for basement walls?
Yes. Drainage cells are installed vertically in basement drainage systems to provide a pathway for water to collect a drain or perimeter drain. They are used in conjunction with waterproofing but are not a substitute for waterproofing.
Can drainage cells be used under a green roof?
Yes. Drainage cells are used under the growing media in green roof systems and roof landscaping systems. The drainage layer conveys excess water to the roof drainage outlets.
Do drainage cells replace gravel?
Not necessarily. They provide an alternative method of creating drainage voids. The choice of whether to use drainage cells depends on the design requirements, loading, soil, water flow, construction details, and the particular project.
Do drainage cells need geotextile?
In many soil-contact applications, a geotextile filter is used in the drainage voids to prevent the ingress of fine particles. The need for geotextile depends on the product and placement.
Can drainage cells support heavy loads?
Certain products can be used in load-bearing applications; however, not all drainage cells have the same load-bearing capacity. The design load of the particular drainage cell and the product used must be verified before placement.
Final Thoughts
A drainage cell is a simple but useful construction component that creates a passage for disposing excess water.
It provides a means for creating a purposeful three-dimensional drainage void and helps control water that collects under planted areas, behind retaining walls, near basements, and over roof gardens and podiums.
A drainage cell rarely works on its own. Its performance depends on the rest of the system around it — the geotextile layer, the waterproofing membrane, the outlet, and the surrounding materials all have to work together for the drainage to actually function.
For this reason, thickness and price alone cannot determine which drainage cell product to use. The right choice depends on the specific loading, soil conditions, water flow, and construction details of the project.