2019-01-02

FoundationDrain – Components, Working and Design

Foundation drain is an exterior drainagesystem installed on the outer face of the foundation wall and near the wallfooting, covered with a layer of gravel, serving the purpose of draining outexcess water seeping into the foundation.

Components andWorking of Foundation Drain

The main component of a foundation drainis a perforated pipe laid all around the exterior foundation, which capturesthe excess water and drains it either towards the storm sewer or a catch basinor soak-pit at some distance from the building.

The perforations are thousands of tinyholes or slits that allow the excess water to enter the pipe, and be drainedaway from the foundation of the structure. The pipe is normally kept coveredwith a mesh permeable “sock” which helps to prevent soil from getting into thepipe. It is then covered by layers of gravel of graduated sizes and finallybackfilled with soil.

The gravel allows water to flow towardsthe drainage pipe, without allowing dirt and debris to clog it up. A weepingtile(porous pipe) is installed in such a way that it slopes away from thestructure and carries the water towards the main sewer system.

DesignConsideration of Foundation Drain

For the design of a foundation drain,various factors are to be considered to ensure an effective draining of water.Some of the factors are discussed below :

1. CodeRequirement

The International Residential Code(IRC), in Section R405.1, requires drains around all concrete or masonryfoundations that retain earth and enclose habitable or usable spaces belowgrade. However, very well-drained soils are an exception and mixtures such assand and gravel do not require drainage.

2. DrainageBoards

In areas prone to heavy rains, drainageboards are used to drain off the water quickly to the perimeter drain byinstalling them on concrete foundation wall. This prevents thebuildup of hydrostatic pressure next to the wall.

3. DrainMaterial

Perimeter drains should be made fromrigid drain tile or perforated pipe. Although flexible corrugated plastic pipecan be used, care must be taken to prevent it from being crushed duringbackfilling.

4. Moisture

The moisture content of the soil placednear the foundation has a great effect on the water drainage from footing asthe moisture content is dependent on the type of soil placed.

5. Trees

According to the U.S. Department ofHousing and Urban Development, trees should be planted no closer to thefoundation than their eventual height. This prevents tree roots from fillingperimeter drains and inhibits the tree from sucking all the water from thesoil, which could lead to settlement.

6. Placement ofdrain pipes

Drain pipes should be positionedalongside the footing—the best spot is near its base. Although tile doesn’tneed to be sloping, low spots (which can be filled with silt) must beavoided.

Types ofFoundation Drain

1. French Drain

This type of foundation drain uses aperforated pipe that is laid beside the foundation wall structure. The slope ofthe pipe is kept away from the structure. The backfilling is done with porousmaterials such as gravel for easy flow of standing water from the surface tothe drain pipe.

2. Footing Drain

This is a highly effective waterdrainage system. A pipe is installed around the perimeter of the foundationwalls on level with the footing. This pipe collects any water that would haveleaked through the top of the footing into the basement and drains it away fromthe foundation walls. The drain is covered with gravel up to the soil’ssurface.

Advantages ofFoundation Drain

1.     [endif]It prevents water accumulation near thefoundation and hence reduces the risk of settlement. Stagnant water may alsoencourage the breeding of mosquitoes and decay the plants.

2.     [endif]Soil erosion can be reduced byinstalling a foundation drain.

3.     [endif]Proper draining of water can help removetoxic and deleterious organisms from the stagnant water.

Disadvantages ofFoundation Drain

1.     [endif]Installing a drainage system is a costlyinvestment. It requires skilled and professional labours.

2.     [endif]Use of perforated pipe has adisadvantage of getting clogged regularly due to the accumulation of silt inthe pipe. Hence the maintenance of foundation drains is hectic.

3.     [endif]Contamination of water bodies –According to the study, subsurface drainage systems can carry nitrate throughthe drain pipes, channelling it directly into the bodies of water such asstreams, rivers and lakes.

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