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What Is Raft Foundation Construction

Last Updated Jun 8, 2011 · Written by Jaclyn Fitzgerald

When building a new home, it is vital that you get the foundations right or you might find your home moving, cracking, or even sinking over time. One option for your foundation is raft foundation construction. Here’s what you need to know.

What is a Raft Foundation?

A raft foundation is a type of foundation that spreads the load from a building or structure over a large area.  They are generally a slab of concrete that extends over the entire area of the building, and the concrete can be stiffened by ribs or beams in order to provide extra strength and to help with the distribution of the load.  Raft foundations are ideal for use on softer or looser soils as they spread the load so well. They can also be used when a standard strip foundation would cover more than half of the ground area underneath the building, or when there may be movement in the deeper soil levels (such as areas in which there has been previous mining).

Using Raft Foundations

Because the raft foundation distributes the load evenly over an area, it will not have areas of pressure that can cause soil settling that will damage the building. A raft foundation is usually laid on a hardcore or scalping bed and the foundation is thickened at the edges. The exterior walls are generally built upon these thickened edges as are the inner walls.

Raft foundations can be a very effective form of foundation construction but you will need to consult with an engineer to make sure that it is the right choice for your soil conditions.
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