Types of Foundations

Posted by subash Monday, September 20, 2010

Welcome to the world of Residential Construction -- our next series. This is the segment of the construction industry that affects most of us. It is, therefore, useful to know more about your house and what goes on to hold it!!! The first article is about foundations -- the feet of your house.
Obtaining an understanding of foundations is critical to recognizing and fixing commonly occuring problems in your crawl space and basement. There are basically 4 types of foundations used most commonly in residential construction:
Pile Foundations: A pile is a column that transfers the load of the building to the soil. A beam is placed under each load-bearing wall and the ends of the beam are then supported on piles. Piles can be made from steel, pressure-treated wood or concrete. Such foundations are useful for either very "heavy" buildings, or in regions where the top soil is unstable, prone to erosion etc. The pile is dug into the earth until a stable soil layer or rock formation is reached. Another application is in places where spread footings are impossible to construct due to topography (like very steep sloping sites). In such situations, piles are the only solution.
Continuous or Spread Footings: As the name suggests, these foundations are constructed along the entire length of the wall. The width of the footing is more than that of the wall. Hence, the load of the structure is "spread" over a large area. Spread footings are made of concrete. They are placed below the frost line (where applicable). Reinforcement steel is used to give strength to concrete in tension. A variation to the spread footing is the Step Footing. This is made by creating a stepped pyramid of brick layers over a large concrete pad. Step footings are common in many parts of the world.
Foundation Walls: Generally seen in accessible basements, foundation walls transfer the load of the building to the foundation. Such walls are usually made of poured concrete, but more commonly, of hollow concrete blocks. Sometimes brick and stone is also used. The concrete walls are reinforced with steel against the tensile stresses generated due to the top loading (of the structure above) and the puch of the surrounding earth. When steel is used in hollow concrete blocks, concrete must be poured to hold the steel in place.
The copyright of the article Types of Foundations in Building Construction is owned by Shefali Kumar. Permission to republish Types of Foundations in print or online must be granted by the author in writing. 
Mat Foundations: In certain situations, especially where the natural water table is high, a mat or raft foundation is used. This is basically a concrete slab the same size as the building. It is reinforced and distributes the load of the building evenly over the given area. This is also useful when the soil is uneven and will settle under focused loads.

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