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How to lay house foundations

Updated April 17, 2017

The foundation of the house is arguably the most important component; it is, at the very least, the part of the structure which -- if built incorrectly -- can have serious consequences, both structural and financial. Knowing how to correctly lay the foundation for a house is critical in ensuring that the construction gets off to the best start, and good preparation can save time and money.

Employ consultants and engineers to carry out ground investigation reports. These will tell you the quality of the soil in which the foundation will be dug, and will recommend depth of excavation and concrete required to properly support the weight of the house.

Draw some building plans and ensure that they are approved by any local authorities. Constructing a house without approved plans can cause legal issues, which is often costly.

Employ a competent groundworks contractor -- someone who specialises in substructure construction -- to assist you in this process. They can provide advice as well as carrying out works involving heavy machinery.

Using an excavator driven by a qualified operator, scrape away the topsoil from the ground to reveal the subsoil. Topsoil is usually about six inches deep.

Mark the centre line of the foundation onto the soil using spray paint, using engineering layouts and coordinates to mark your foundation in the right area. Use batter boards to mark out the corners.

Employ the groundworks contractor to dig the foundation trench to the required depth.

Dependant upon the condition of the ground, reinforcement may be required to provide additional support. This is usually in the form of a steel mesh, which is laid into the trench and raised off the ground slightly using metal supports known as "chairs".

Pour the concrete into the trench to the required depth, and employ the groundworks contractor to remove any trapped air in the concrete by using a large vibrator rod. Allow to dry for two to six weeks, dependant upon the depth of concrete.

Build trench blocks on top of the concrete to the required level, or engineering bricks and concrete blocks if the foundation design states as such. Lay any pipework or drainage that passes through this wall. Backfill the trench with the excavated soil.

In the enclosed area formed by your foundation, lay and evenly spread gravel, as well as using gravel to backfill French drain trenches, where rainfall filters through the gravel and into the drain, which is perforated with small holes.

Lay a damp proof membrane (a waterproof plastic sheet) over the gravel and the blocks. This prevents water from rising through the walls and causing rot.

Fill the area with concrete to the required depth, and 'tamp' it. Tamping is the process whereby trapped air is removed from the concrete through repeated strikes with a long plank of wood held by two people.

Smooth this off using a wooden or plastic float to provide a suitable finish on which to lay your floor.

Leave the concrete to dry for two to eight weeks, depending upon the depth of the slab.

Tip

Always check the references of any groundworks contractor to ensure suitability. Ensure that all operators of heavy machinery hold the correct certification and/or qualifications, to guarantee their training and reduce the risk of poor quality work.

Warning

Building without sufficient planning approval can cause legal problems. Overlooking a foundation design can cause future problems, such as subsidence.

Things You'll Need

  • Foundation designs
  • Engineering reports
  • Ground investigation reports
  • Plumbing layouts
  • Drainage/service layouts
  • Vibrator rod tool
  • Excavator
  • Concrete
  • Steel mesh
  • Steel chairs
  • Gravel
  • Trench Blocks
  • Concrete Blocks
  • Engineering Bricks
  • Batter boards
  • Spray paint
  • Waterproof plastic sheet
  • Concrete smoother
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About the Author

Ben Wakeling graduated from Coventry University in 2009 with an upper second class honours B.Sc. degree in construction management. Wakeling is also a freelance writer, and works for a number of businesses, such as Demand Studios, Suite 101 and Academic Knowledge.