Slab-on-Grade vs. Framed Flooring

Residential Building Blocks

• To compare slab-on-grade to elevated framed flooring systems, it helps to know how each of these systems fit into the home construction process. A slab-on-grade foundation consists of a concrete slab, several inches thick at ground level. House sites for these foundations require soil tests, machine grading and sometimes fill before slab construction begins. The slab rests on buried footings, though some slabs are thickened along the edges, combining footings and slab into a single unit. Framed flooring construction include foundations with continuously poured perimeter walls, pier-and-beam construction or a permanent wood foundation on appropriate code-required footings.

Foundations, Designs and Sites

• Slab-on-grade foundations require a level site, or a site suitable for grading, fill and compaction, as long as the soil conditions meet local building code requirements. Slab foundations work best for homes with entrances at finished grade level. The foundation consists of strong footings and reinforced concrete on a bed of gravel that is covered by a vapor barrier to prevent moisture or water wicking into the concrete. For sites with uneven or sloped surfaces, wood-framed foundations can more easily adapt to these sites. Home designs that call for an above-grade entrance and elevated decks work better on raised foundations with framed floors.

Pros and Cons of Slab Foundations

• The primary benefit to a slab-on-grade design lies in material costs and its ease of construction. Slab foundations can go up in a few days or less, but the curing time and weather conditions needed for building a concrete slab foundation can slow or hinder the building process. A durable material, concrete makes sense for homeowners who plan single level ranch-style homes or radiant in-floor heating systems. One common complaint against a slab-on-grade foundation is its cold, hard nature. Compared to raised wood-framed floors, some homeowners find concrete floors uncomfortable underfoot. In addition, builders must bury plumbing lines in concrete when constructing a concrete slab, which makes for difficult repairs or relocation of these lines in the future.

Pros and Cons of Framed Floor Foundations

• Raised foundations with framed floors provides convenient access to plumbing, HVAC and electrical lines underneath the floor of the house via a crawlspace or basement. Raised foundations make it easy to make repairs, renovate the home or make modifications when necessary. Framed floors give the home an elevated profile compared to a slab-on-grade, which can add to the home's curb appeal. Framed floors offer a cost-competitive advantage over slab-on-grade foundations, especially when having to grade, add fill or compact the graded site to construct a concrete slab. And because plumbing and other systems are installed after the foundation is framed, you do not have to wait on a plumber's schedule to begin foundation construction.