Strip Footings

Strip footings are the foundations required when building a double brick or brick veneer house with a timber floor. The outside walls of the house are bricked up to floor height and then the floor is installed. For this to be able to be done correctly there must be a strong foundation for the house to sit on. This foundation is called a strip footing.

This is a reinforced concrete beam installed into soil that is laid around the entire outside of the house.

The set out is done by placing hurdles/profiles so that two string lines can be attached and can be placed on the outside of the building line. Place a string line for the outside of the footing and another one for the inside of the footing. It is important that the hurdles are placed a minimum of 3 metres from the building line so that a backhoe can dig the trenches without running over the hurdles. The footing should be located as per your approved building plan and so the brick wall can be attached or laid on top of it.

Footing trench excavation

So the backhoe operator is able to dig accurate trenches the trenches need to be marked out on the ground. To do this place a straight piece of timber under the string lines, make sure it is plumb and then mark with lime. The string lines are removed after the trenches have been marked so the backhoe can get in. Use a level to make sure that your timber is plumb under line and then mark the ground with the lime or you can use spray line marking paint. This is done under the outside and inside lines for the foundation so the backhoe operator knows exactly where to dig. After the trenches have been dug follow up with a shovel to make sure the trenches have been cleaned up and the corners squared up. Care must be taken so that the sides of the trenches do not collapse under load and trenches over 1.5 metres must be shored so they are safe.

Design

The design of the Strip footing needs to be prepared by an geotechnical engineer so that the type of ground and the slope/drainage is taken into account. Also on a sloping site a stepping strip footing may be required. The, stepping strip footing steps down with the slope of the land. The steps in the footings step down to match the height of the brick that will be laid on the top. This allows the brick layer to lay brick straight on the footings without the need to cut the bricks down. As cutting of the bricks is time consuming thus will cost more money.

Laying the Reinforcement mesh

The size and type of the trench mesh will be on your approved plan. Place the mesh on bar chairs and place in the trenches. Make sure that they fully overlap at the corners and any joins overlap by the required amount on your plans. All bar mesh needs to be wired together at T sections and corners and any joins. The top and bottom mesh are wired together with a gap between. This is done by wiring bar spaces to the bottom and top mesh around the complete building line.

Pouring the concrete

When pouring the concrete ensures that the concrete truck does not get to close to the trench as the trench may be damaged. However if you do not have good access to the site a concrete pump will be required. When working out the volume of your concrete (depth x width x length) allow extra concrete as the trench will not be perfect. It is necessary to round up to the nearest 0.2 increment as a minimum however more may be required so evaluate your site. It is better to have a bit too much concrete then not enough. Concrete can only be poured after the trenches and mesh have been inspected by your council building authority.