Foundations: what you need to know

Okay, so, you’ve done the site research, the layout planning is done, and you’re ready to start laying out your foundation. Here’s what you need to know.

There are five main types of foundations common to the low-rise buildings within which the domestic housing category falls. The type of terrain you are building on will determine what type of foundation you will need to use.

Foundations and how they work.

trench fill

strip foundation

wide strap base

raft foundation

pile foundation

An important note. When you expose your trench, you need to get building control, NHBC, or an independent structural engineer to survey your land before you pour your foundation. Forgetting to do this could mean digging up the foundation at worst, especially if the soil isn’t suitable for the type of foundation you intend to pour.

Stay safe and do your inspections.

Filling of trenches.

Trench backfilling refers to a technique used to backfill deep foundation trenches. What happens is this, you go to the site and dig for your foundation, but you end up about 1600 or maybe even 2000mm below grade. Well, obviously, you don’t want to fill that entire depth with a good strong foundation concrete, so you order a weak concrete mix from your ready-mix concrete company and pour it into the trench to the depth you propose to lay the foundation. . concrete. The trench backfill should be as strong as good supporting soil to provide a suitable foundation for the strip toe.

Strip Foundation.

A strip foundation is the simplest form of house foundation. It consists of a Gen 1 grade concrete placed to a width of 650m wide and usually to a depth of 350mm, with reinforced steel at the top or bottom of the foundation or in some cases both. It is preferable to have an engineer design the foundation for you and provide dimensions before you begin. Strip foundations are being replaced by wide strip foundations and are now relegated to supporting internal walls within the home.

Wide Strip Foundations.

Wide strip foundations are similar to ordinary strip foundations, except that they are wider. They are made wider to spread the load over more floor area. The wide strip foundation is generally used in poorer supporting soil conditions. Wide strip foundations are generally 1m wide x 450mm deep, with reinforced steel at the top or bottom of the foundation or in some cases both, although other dimensions may be specified by an engineer. depending on the soil conditions and the load that is imposed on the foundation.

Raft foundations.

Basically, it is a concrete slab placed on the foundation of the house with reinforced steel supporting the concrete. While the raft base is still in use, it is slowly going out of style as there is a tendency for the raft to tip in very poor ground conditions.

Pile foundations.

As good quality sites become scarce, construction is now being done on poor and weak soils that had previously gone untapped. Weak or fluid soils or soils that contain a large proportion of compressible elements are prime candidates for piling. A pile is simply a square piece of concrete with four reinforced steel bars running through it.

The pile is normally 350mm square depending on engineers specifications and can be 4m to 12m in length. This is normally at crossroads and intersections inside the house. They are beaten until they refuse. That is, they will not go down any more.

Once all the piles are driven, the tops are cut off leaving just enough exposed steel to tie to the beams. A 50mm layer of mud or concrete is then placed over the site. Then the line of the house and all internal load-bearing walls are marked. A small retaining wall is then built on each side of the piles to form a trench into which the foundation can be poured.

Once the block work has been completed, reinforced steel is placed in the area where the concrete is poured and, based on engineers’ designs, is placed and tied to form a steel cage that forms the base of the foundation. These are tied at the top of the piles. Once the steel has been placed, fastened, and tied, the concrete is poured in the same manner as a strip or wide strip footing.

All you have to do now is wait until the concrete hardens and you can start building your house. Normally, with piled foundations, prestressed slab floors are used. This is a very safe and fast construction method.