The foundation may stiffened by ribs or beams built in during construction which will add extra strength and rigidity.

Pour the concrete over the reinforcement.

Lay reinforcement on spacers over the foundation bed.The foundation bed is then compacted by ramming.Raft Foundations are built is this following steps: Rafts are most suitable when the ground is of good load bearing capacity and little work is required to get a solid foundation. The raft is laid on a hardcore, or scalping bed and usually thickened at the edges, especially in very poor ground. How Do Raft Foundations Work?Ī raft foundation spreads the weight of the building over the whole ground floor area of that building. To understand when it is better to use raft foundations, you need to understand how they work. They are much more commonly used in the construction of commercial building in the UK that they are for domestic homes, but can be used very successful in both situations.

There are also situations (usually in areas where mining has occurred) where there may be areas of movement in the strata. Rafts are most often used these days when the strata is unstable or (because of this) a normal strip foundation would cover more than 50% of the ground area beneath the building. Raft Foundations – How to make raft foundations are made When Are Raft Foundations Used This made the entire operation much more difficult and time consuming so raft foundations became less widely used almost overnight. This meant that to use a raft foundation, it had to be designed and approved by Building Control. When the Building Regulations were introduced in 1965 there were no generic rules for raft foundations as there were for strip foundations. The raft foundation was cheaper, easier to install and most importantly, did not require as much excavation as the usual strip foundations. The slab is spread out under the entire building or at least a large part of it which lowers the contact pressure compared to the traditionally used strip or trench footings.īecause of the speed and volume of houses required after the second world war, the raft foundation was widely used. Raft foundations (sometimes known as Mat Foundations) are a large concrete slab which can support a number of columns and walls.

Ark floating foundation