Post and pier construction is a technique used to build the foundations of a house quickly and cheaply. This type of construction is characterized by lack of a perimeter foundation or foundation pad. It is often employed in the tropics and in flood-prone regions, for reasons which will become apparent shortly, and it is also commonly used in low-cost construction.
In some regions, these foundations are not permitted, due to concerns about safety. New homes must be constructed using a different foundation method, and older homes may require retrofitting to be sold or insured. In other regions, this construction technique is perfectly acceptable, and sometimes even preferred.
In post and pier construction, the weight of a home is distributed across a series of posts installed under the home and mounted to piers, which are wedge-shaped concrete blocks that distribute the weight across the ground. Typically, posts and piers are mounted all the way around the perimeter, and at key points in the middle of the home to ensure that the floors, and the rest of the house, do not sag.
Obviously, a home which has been built using this construction method does not have a basement, because the house is elevated. It is not uncommon to use cladding or facing between the ground and the floor of the home so that the underside of the house is not exposed, although in some regions, this area is left open.
In areas where flooding is common, post and pier construction can significantly reduce flood damage, as the house is lifted above the water. Areas prone to subsidence can also be suitable for this construction method, as a perimeter or slab foundation would crack, whereas individual posts and piers can be jacked up and replaced as needed. It also tends to keep insects out and reduces mold, mildew, and rot, because it promotes air circulation under the house and lifts the house out of range of insect pests.
The danger of post and pier construction is that, if posts or piers start to fail, it can be very dangerous. In perimeter and slab foundations, the weight is distributed very evenly, so a partial failure or crack is an issue, but not an immediate safety problem. In post and pier homes, the weight is concentrated on the individual spots, so if something breaks, rots, or shifts, that area of the house may start to sag. In extreme cases, a house may even crack open as the weight shifts across the remaining posts and piers.