When it comes to designing a foundation for a new home or structure, you've got several options you can choose. One of these is a post-and-beam foundation, a traditional approach that incorporates both concrete and wood. Post and beam is a comparatively cheap alternative, but may be unsuitable for many kinds of structures and regions.
Post-and-beam foundations feature wooden posts mounted on concrete blocks called footings. The structure transfers its weight to the footings via these wooden beams. They are similar to post-and-pier foundations except that those foundations use concrete piers rather than wooden beams. Sometimes post-and-beam foundations use crushed rock for the footing rather than concrete. The resulting foundation isn't embedded as deeply as it would be with some other designs but is relatively cheap and simple to construct.
Climate makes a significant difference to post-and-beam construction. Homes built in regions with a cold climate require deeper footings; the bottom of the footing must rest below the depth of frost in the soil so that freezing during the winter doesn't lift the footings. Homes built in milder climates don't face this challenge and therefore do not usually require the same precautions. Using pressure-treated wood posts can enhance the strength of the foundation in either climate.
The footing should always rest on soil that has not been disturbed and is relatively free from organic material. Post-and-beam foundations should never be built atop fill or dumped soil, excepting crushed rock in certain circumstances. Larger footings help to spread the weight across a broader area and may be helpful if you are in doubt about the soil's ability to support the weight of the structure.
Post-and-beam foundations are only suitable for small houses in certain parts of the country. The lateral stresses induced by earthquakes can wreak havoc with post-and-beam foundations, and they are also quite vulnerable to hurricanes, so you should never use this style of foundation in earthquake or hurricane country. If you've inherited a post-and-beam foundation, you can use lateral bracing to improve its strength and help make it more resistant to earthquakes. Ultimately, however, a perimeter system will still be a more durable option.
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