Facts on Foundation Types for New Home Construction

A firm foundation, we are told, is essential to building a house which lasts. In new home construction, foundations come in many types. In the Southeast, common foundations are raised foundations with crawl spaces, foundational pilings, raised slab and slab on grade.

 

No basements in Charleston

The most traditional type of foundation is that built around a basement.  However, in Charleston we don't have soil conditions that allows for the digging of a basement. We are so close to sea level, that when you dig a hole deep enough for a basement foundation, it most likely will fill with water.

For areas in greater Charleston which are near the water or in flood plains, FEMA requires specific standards for coastal flood zones.  “Foundations in coastal areas must be constructed such that the top of the lowest floor (in A zones) or the bottom of the lowest horizontal structural members (in V zones) of the buildings are elevated above the BFE (ed: base flood elevation), while withstanding flood forces, high winds, erosion and scour, and flood borne debris. Deeply embedded pile or other open foundations are required for V zones because they allow waves and floodwaters to pass beneath elevated buildings. Because of the increased flood, wave, flood borne debris, and erosion hazards in V zones, NFIP design and construction requirements are more stringent in V zones than in A zones.”

 

Raised timber pile foundations

According to Raised Floor Living Pro, “Pile foundations are also used in coastal areas where the foundation may be subject to inundation and possible wave action. Elevated wood pile foundations enable buildings to be constructed above the base flood elevation.” In the coastal Lowcountry, areas adjacent to rivers, beaches and marshes generally are locations where you will see homes which appear to be built on stilts. These timber piling foundations elevate the home based on FEMA codes to keep the home above inundation by flood waters.

 

Raised foundations with crawl spaces in Charleston

Rather than a basement foundation, in the Charleston area, upscale homes are constructed with a raised foundation with a crawl space. The site is prepared by grading and removal of all organic debris such as tree stumps and roots.

Footings are built and perimeter foundation walls are erected. Foundation walls are generally built of cement block with a parge coat of cement. They are built to follow the footprint of the house. Pier footings are used to support the interior of the home. Flashing tops the foundation wall and the sill plates are placed on top flashing and the sill plates bolted to the foundation.

The advantages of a raised foundation with a crawl space include easy placement of and access to plumbing, electrical and HVAC ductwork. Work on the foundation can proceed separately and ahead of the work on wiring and ductwork whose inspections take precedence when they are installed in a slab on grade foundation.

Homes on raised foundations may offer some protection against flooding. In areas of the Lowcountry which are in floodplains, specific regulations apply requiring elevated homes on foundational pilings. Most upscale homes such as those built by PulteGroup’s John Wieland Homes are built with a crawl space foundation.

Disadvantages to foundations with crawl spaces are the opportunity for development of mold and mildew in the crawl space. Encapsulation of the entire space with adequate sealing and vapor barrier installation prevents the growth of mold and mildew. Crawl spaces may also provide a hiding place for critters and insects leading to pest control problems. However, with correct care, crawl space encapsulation, this is not an issue.

 

Slab on grade foundations

Slab foundations are the norm for most new construction homes in the greater Charleston area. Frequently referred to as slab on grade foundations, these concrete pads provide a very stable foundation that prevents uneven, creaky floors and helps your home feel solid. Slabs are thicker at the edges to create footings and help support the house’s walls.

To construct a slab foundation, the home’s location is graded to cause water to drain away from the house, and a foundation area is cleared of organic debris and leveled. Foundation forms or boards are set in place. Gravel is placed in the area and topped with a moisture barrier. Plumbing, waste and water lines are installed prior to the pouring of the slab. Rebar is placed in the footing areas prior to the pour. Concrete is poured over wire mesh to provide strength and reduce cracking.

Slab on grade foundations are generally very sound and make a quiet home. Some people don’t care for slab foundations because they prefer the appearance of a home on an elevated foundation. One of the primary disadvantages to slab foundation is the difficulty of access to repair plumbing line leaks. Floors must be dug out through the slab to get to and repair lines. When you have a house with a slab foundation, HVAC ductwork is run through the attic.

 

Raised slab foundations

Raised slab foundations are common in the Southeast and are a hybrid between a raised foundation and a slab on grade foundation. They elevate the house above grade, help prevent water intrusion from rains and generally create a more aesthetically pleasing appearance.

For a raised slab foundation, footings are dug and a foundation wall constructed of concrete block outlining the footprint of the home. On top if this crushed stone or fill dirt is placed and leveled. A moisture barrier is installed on top of the crushed stone. Topping this is a concrete slab reinforced with wire mesh. Plumbing and water supply lines are laid in the slab before the concrete is poured.  Moisture barriers or flashing and sill plates are installed so the house’s exterior walls can be constructed.

 

Talk with your homebuilder about their foundation construction

While many people have a preference for one type of foundation over another, each when constructed by a professional, trustworthy home builder gives you a solid base for your home. Ask your builder’s representative to show you examples of their foundations, go over their construction process and explain why the foundation they use is most well suited for the neighborhood, location and home they are building for you.

 

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