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How does a Foundation Drain work?

Doug Lynch

Tuesday, July 1, 2014 • 12:00am

How does a Foundation Drain work?

Sometimes there is enough snow melt and/or rain to make the water rise around the house. This is known as a high water table or perched water. If this water was to remain adjacent to the foundation it would eventually enter the building because concrete is porous. Therefore many building codes require perimeter drains around the outside of basement footings. These are known as Foundation Drains or Footing Drains. These drains are mandatory for some newer homes. So, how does a foundation drain work?They are not difficult to install before the foundation has been backfilled, but they are costly to put in after the fact. Foundation Drains are installed during initial construction to prevent basements from becoming wet when groundwater is either adjacent to or higher than the floor.

What is a Foundation Drain?

Foundation drains are installed at the bottom of the foundation to divert the water that gathers around the house. These drains run around the exterior of the foundation wall at the footing. When properly installed, footing drains eliminate hydrostatic pressure at the foundation and prevent water at the exterior of the foundation from finding its way into the basement. To protect the bottom of the foundation of a house from water, it's a job worth doing right.foundation drain

A Foundation Drain Typically has Three Components:

  • The drain pipe. This pipe is usually made of High Density Polyethylene (HDPE) plastic and is perforated to allow water infiltration. The standard pipe in this application is 4-6” and goes around the entire footing. It should be a contiguous system with the design having to consider the slope of the lot.
  • The filter fabric and stone. The foundation drain system is usually protected by placing gravel and filter fabric under and around the pipe. First the filter fabric is laid with the excess fabric placed away from the foundation. The crushed stone and pipe is installed and the excess fabric is folded over the trench with more stone. Then sand placed above will prevent soil from washing into the fabric and clogging its pores.
  • The delivery system. The foundation drains have collected the water accumulations at the base of the foundation and must now be diverted away from the structure and into a drainage system. The collected water is then directed toward an on-site dry well or off-site storm water system which is fed by gravity graded from the foundation to the lower collecting place.

basement-resized-600  After the foundation drain is installed the backfill occurs. Unless you were there to witness it you don’t know if the builder used the same dirt from the excavation or filled the backfill with debris from the jobsite like tree roots. You also don’t know if the backfill was tamped or compacted in any way. The foundation drain is as old as the house and has probably failed to some degree. These exterior drains are subject to soil pressure and soil movement. Foundation drains are not covered by homeowners insurance because they are not permanent are will fail over time. http://www.blogsdb.comD

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