How to lay house foundations

Written by ben wakeling
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How to lay house foundations
Building the dream home requires a solid foundation. (house blueprint and house model studio isolated image by dinostock from Fotolia.com)

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.

Skill level:
Challenging

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Things you 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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Instructions

    Constructing the Foundation

  1. 1

    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.

    How to lay house foundations
    The quality and nature of the soil is important. (cracked soil image by Ana de Sousa from Fotolia.com)
  2. 2

    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.

    How to lay house foundations
    All plans need to be approved. (house plan image by Jon Le-Bon from Fotolia.com)
  3. 3

    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.

    How to lay house foundations
    A contractor can provide valuable advice. (builder and architect image by goce risteski from Fotolia.com)
  4. 4

    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.

    How to lay house foundations
    The topsoil can be stored or taken off site. (digger image by Edvin selimovic from Fotolia.com)
  5. 5

    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.

    How to lay house foundations
    Choose a bright colour for the spray paint. (spray image by Dragana Petrovic from Fotolia.com)
  6. 6

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

    How to lay house foundations
    (construction vehicles on the site digging a trench image by Elnur from Fotolia.com)
  7. 7

    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".

    How to lay house foundations
    Steel mesh is often laid in two layers. (roll of mesh image by jimcox40 from Fotolia.com)
  8. 8

    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.

    How to lay house foundations
    The concrete should cover the steel. (cold concrete blocks image by jbattx from Fotolia.com)
  9. 9

    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.

    How to lay house foundations
    There are often two to three courses of blockwork. (Structure from blocks image by amlet from Fotolia.com)

    Constructing the Floor Slab

  1. 1

    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.

    How to lay house foundations
    Gravel helps prevent ground moisture from rising. (gravel image by Alison Bowden from Fotolia.com)
  2. 2

    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.

    How to lay house foundations
    Rainfall is the main source of rising moisture. (rain image by tomash from Fotolia.com)
  3. 3

    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.

    How to lay house foundations
    A plank of wood is ideal for tamping. (plank image by Adrian Hillman from Fotolia.com)
  4. 4

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

    How to lay house foundations
    Any flooring can be laid on a smooth finish. (concrete image by Empath from Fotolia.com)
  5. 5

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

    How to lay house foundations
    Quick-drying concrete can be dry in a week. (time image by Deborah Durbin from Fotolia.com)

Tips and warnings

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

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