How to build a house foundation

In this article we will explain how to build a house foundation from scratch.

Before you get stuck into digging the trenches for your house, make sure you have set out the house properly. Read our guide on how to set out a building here.

What will you need?

  • Fishing line or builders line
  • Spade
  • Round nose shovel
  • Square mouth shovel
  • Pick head and handle
  • Good quality measuring tape
  • Brick jointer
  • Folding hardwood rule
  • Fibreglass long tape
  • Line level
  • Club hammer (1.8kg)
  • Brick bolster
  • Cold chisel
  • Wrecking bar
  • Broom
  • Plumb bob
  • Brick trowel
  • Pointing trowel
  • Gauging trowel
  • Chalk line (Reel)
  • Refill Chalk
  • Level
  • Latex knit, heavy duty work gloves
  • Dust mask
  • Box of crayons
  • Concrete wheelbarow
  • Hosepipe
  • Steel squares

Trenching

Set out “Profiles”. From the outside perimeter of the house, measure out at least 1 meter and put in more pegs, with a piece of wood nailed horizontally across the top of two pegs. This is to mark the corners of the foundations.

Measure the width of each foundation trench (e.g. 600m) and knock a nail into the top of the piece of wood of the “Profiles”, to mark the foundation width. Attach a piece of string to each nail and stretch across to the opposite side, marking the foundations. Trenches are different sizes, depending on loading.

Mark the ground under the string with a spade. Once again knock in nails to the piece of wood, this time measuring the width of the wall (220mm). The wall must be exactly in the centre of the foundation. In a 220mm wall, the foundations must be 190mm for a 600mm trench, more on either side of the wall.

Digging the foundation trenches

Now you can start to dig the trenches up to 600mm deep, using the lines you have made with a spade. Make sure the sides are as plumb as possible, and the bottom as level as possible.

Fix pegs in trenches, about 1,5 meters apart, and 200mm high. This will show you what level to pour the concrete to.

Try to make the sides and plumb and the bottoms as level as possible and be sure to compact the bottoms of the trenches. Any steps in the foundation should be at the at the same height as the brick course. Once done, fix pegs at the bottom of the trenches to indicated the depth at which the concrete is to be poured.

Footings

Once you have mixed the concrete, pour it into the trench, to the height of the top of the pegs. You must pour the concrete for the foundations in one day. Start pouring the concrete at the corner furthest away from the mixing site.

Level the concrete to the top of the pegs with a board, Ram down the concrete into the corners with a stick to get rid of air bubbles and spaces.

Leave the foundation concrete to cure for three days before building on it.

Pouring the foundation

The concrete for the foundations should be poured in one day so that there are no seams in the foundation and the entire foundation will cure as a whole leaving no weak points.

Start pouring at the corner that is furthest away from the mixing site and pour the concrete the the level of the top of the pegs you placed in the trenches.

Be sure the ram the concrete down in the corners with a stick to get rid of air bubbles and spaces.

Finally, level the top of the concrete to the top of the pegs.

Leave the foundation concrete to cure for 3 days before building on it.

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