Since St. James Plantation, and similar communities surrounding Southport, NC, draws people from all over the United States, it is important to understand some of the nuances of building in a Southeast coastal community. And since foundations provide fundamental structural support for any house, it is important to understand the types of foundations used in southeast coastal Carolina. There are three primary types of foundations: full basements, crawl spaces and concrete slabs. (Although right along the coast houses may also need to be built on foundational pilings.) Of the three primary foundations, basements are a rarity in coastal regions because of the flat terrain and high water tables. The two most common types of foundations found in southeast coastal communities such as St. James Plantation are a crawl space foundation or a concrete slab foundation. W. Epstein, a St. James builder, says he is often asked which is better, a crawl space foundation or a slab foundation. He says that each of these foundations has its advantages and disadvantages. The June 12, 2012 article, “St. James Plantation Custom Builder Encourages Green Crawl Spaces” discussed the crawl space foundation. Therefore, this article will focus on slab foundations.
A slab foundation is as its name implies—a flat, thick piece of concrete poured on the ground. It has no basement or crawl space. There are several methods of constructing a slab foundation. It is always prudent to ask your builder how he constructs his slab. But typically slab foundations in upscale communities such as St. James Plantation use a poured concrete footing, and a block foundation (3 courses or more) that is filled with dirt and compacted. A 4”-6” slab is then poured over the ground that is covered with a 6 mil polyurethane plastic sheet and reinforced mesh wire.
One advantage of a slab foundation is that it generally costs less to construct than a crawl space. Although the actual cost savings may be minimal if the slab needs to be built up for proper water drainage and aesthetic purposes. A slab is most cost effective if the ground is level and the building lot is at or higher than the grade of the road. If the building lot sits down off of the road or the building area is low then additional block and fill dirt will be required to elevate the slab, which offsets some of the cost savings of slab construction. If the slab is not elevated properly, water may not adequately drain from the house or the house may be prone to water infiltration with heavy rains. Raising the slab will not only prevent water issues but it will also help avoid a “squat” appearance of the home, where porches are at grade rather than being elevated above the yard.
Another advantage of a slab foundation in the coastal southeastern US is that it is a slab and not a crawl space. A crawl space, unless constructed as a “green” crawl space, will, overtime, develop moisture problems which can lead to mold and mildew, buckled floors, musty orders in living spaces and damp wood that termites love to chew. And the floor of a slab built home generally maintains a more constant temperature since there are no air pockets around the floor as there are with a crawl space.
The major disadvantage of a slab foundation is that the plumbing drains and water supply lines are not accessible once the slab is poured. If electrical outlets are desired in the floors those wire conduits also need to be put down before the slab is poured. So careful planning of the plumbing and electrical floor outlets is essential prior to constructing a slab foundation home. Other mechanicals such as the HVAC ducts and the majority of electrical wiring can be run through the attic and walls; and they remain accessible after moving in, although admittedly access is not as convenient as having a crawl space.
Bill Epstein, custom builder in Southport and St. James Plantation, says, “The type of foundation is ultimately the decision of the property owner. What is most important, if the owner decides on a slab foundation, is to talk with the builder about elevating the slab to ensure that water runs away from the house. It is also important to elevate the slab to give the house more curb appeal by avoiding a squat appearance or the ‘built in a hole’ look.”