A drainage board is a special material that allows water to move through and away from it without sacrificing structural stability. These boards are used in a wide range of construction, particularly in places with a lot of rainfall or areas where a constructed surface is often saturated with water. Most drainage boards have hundreds of small pockets that collect water from above surfaces; this makes them look a lot like a giant egg carton. In addition, the Internal Drainage Board is a government body in the European countries of England and Wales that oversees special drainage issues within those areas.
The construction of a drainage board gives it a very unique appearance. The board itself may be as thin as a plastic floor mat or as thick as 2 inches (5 cm), but it is always covered in pockets. In the thin boards, these pockets look like small dimples. In the larger boards, they are generally as deep as the board itself and proportionately wide. When in place, the opening for the pockets goes up and the bottom goes down.
The main purpose of a drainage board is to pull water downward from upper layers. As water flows into the pockets, it will pull water from above it down as well. The increases the speed at which an area drains, keeping above surfaces dry. At the bottom of the pockets, a one-way permeable membrane will allow the water to flow out, but not flow back in. This keeps water flowing in the correct direction, even when the surfaces above the drainage board are dry.
The most common place to find a drainage board is in building construction. The boards are often placed in the foundation of the building to assist in keeping basements dry. They pull water away from the structure before it has a chance to move through the basement walls.
These boards are also used in some garden designs. They provide adequate drainage for the plants above and prevent weeds and bugs from moving up into the garden from below. This design is also common in roof gardens, where it is very important that extra water be moved off the roof quickly. This is both to remove the weight from the structure and to keep it from seeping down into the building. In this case, the drainage board often sits over a collection layer that moves the water to the building’s drainage system.
In England and Wales, the Internal Drainage Board assists landowners with tricky drainage problems. These areas are prone to drainage issues due to their relatively high water table and high precipitation levels. In addition, this body oversees the construction and maintenance of water pumps, channels and drainage systems in their governed areas.