How to build strip foundations

• Walls up to 1m (3ft 3in) high will require a footing at least 150mm (6in) deep (for a single-skin wall) or 250mm (10in) deep for a double-skin wall.
• If the soil is clay, then a further 100mm (4in) should be added to the depth of the footing.
• The footing should finish 150mm (6in) below ground level and even further in extreme climates, where protection is needed from frost damage.
• The footing width should be 200mm (8in) wider than the wall -100mm (6in) either side.
• On loose, sandy soils, however, the footing should be 400mm (16in) wider than the wall.
• For walls only three or four courses high, shallower strip footings or concrete blocks may well be more suitable.
• Mark out the area of the wall on the ground with string attached to pegs or by using profile boards.
• Use a spade to cut into the soil directly underneath the string and dig out a trench to the required depth.
• If the subsoil is particularly loose, then dig down a little further and fill the space with compacted hardcore.

Once you have dug the trench you will need to lay the concrete footing.

• Start by knocking in a stake at each end of the trench down to the footing depth. Insert more stakes at 1m-2m (3ft-6ft) intervals between them. Ensure all stakes are driven into the ground vertically.
• Moving up the trench, position a spirit level across the top of the stakes to check they are level. Make any required adjustments.
• Mix the concrete to the ratio 1 cement: 5 ballast, adding water to produce a consistency that should pour easily without being too wet.
• Shovel the concrete into the trench up to the top of the stakes. Smooth the surface with a metal float.
• Leave the concrete to harden for 3 days before you start to build the wall.