Post and Pier foundations are most often associated with beach or river front settings. Their main use in those areas is to provide a footing that will support the home over loose soil or sand and also to raise the home above the flood zone level.
Other uses of Pier and post foundations would be to allow for quick building of a home in a rural area where the costs of concrete would be prohibitive or its transport impossible. Another use may be in mountainous areas where a home is set along the hillside supported at least partially by piers.
To the right you can see the beginnings of our Ocean City, New Jersey home. In this area as is true for most beach front property the soil conditions have poor compaction. The use of a standard concrete footing would be both under rated because of its inability to withstand settling and also because there is a high probability it would be undermined by a storm flood.
To support the home correctly you must drive pressure treated pilings into the ground until they reach bedrock. This may only be 10 feet or may be up to 40 feet. In areas that need deeper pilings you may be forced to use caissons. A caisson is a concrete pier that is formed by driving a steel sleeve into the ground and pouring concrete into it.
As you can see we are using a combination of a conventional concrete footing to support the first floor block wall and pilings that will actually support the structure of the home. The pier system is distributed through out the house floor plan. The footing used for the short knee wall is used to define storage and a garage areas and is not considered structural.
The first floor of the home must be located above the flood zone set by FEMA. In this area that is 11 feet. This means that the first floor of the home will be un useable for living. and the second floor is now considered the first floor.
In the picture you can see the red arrow is pointing to the piling. Pressure treated beams are installed on the top of the pilings and then build down or actually hang the first floor stud walls. If there is a severe flood the first floor will fill with water and any home furnishings will be destroyed. In a worst case scenario the first floor walls could completely break away from the beam and the pilings would still support the house.
Once the framing is completed you can see that the home looks rather standard. There are no visible signs of the piers.
Unfortunately because most of these homes range in the 3 to 8 million dollar range the home owners want something that is pretty and not functional.
And since they won’t usually be in the home during winter floods they don’t take the same precautions that a year round resident would to reduce the impact of waves undermining the structure.
In one of our other homes located about 2 miles away a larger threat of flooding is present. For this reason the home owner decided it would be best to have the street level of the house open. FEMA’s preferred method is to provide open areas that are below the flood level to allow flood waters to flow under the house because of this the home has a much better chance of surviving.
Elevation of utilities is also important to reduce the chance of loss of power and or gas and water service. If you look close you may be able to see there is a nook where the Heat Pump and Air conditioner are stored. The gas meter and electric services are also raised about 8 feet off the ground.
If you are building or remodeling a home in a known flood zone there are many added zoning restrictions that must be followed. When choosing a contractor or an architect you should make sure they have previous experience building in flood zones. The easiest way to find out is to ask for reference homes and then ask the Building Official Permits office to confirm that they are listed on a permit or building plan. You should then visit the homes and ask the owners about any problems they may have had since the project was completed.
There are many other applications for pilings or post and beam foundations in home construction. You will see examples in most porch or deck construction and in homes built in unlevel conditions such as mountain or hillsides. Again because of the difficulty and need for special equipment the instillation of the foundation should be performed by a professional but once the sill beams are placed standard construction of the rest of the house can be completed by a owner-builder or a conventional contractor.