Types of floor construction

Written by shane grey
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Types of floor construction
Dimensional lumber joists span the ceiling to create the floor of the second story. (Jupiterimages/Comstock/Getty Images)

Advances in structural engineering and building materials technology allow builders to construct ground floor and second story floors with several materials. Architects and engineers prescribe flooring construction methods and materials depending on environmental factors and load requirements. If you become familiar with the different types of floor construction, you can choose the kind that suits your project's budget and design.

Slab on Grade Floor

The slab on grade, also called a concrete slab, serves as both a foundation and a ground level floor. As its name suggests, the slab on grade is simply a large mass of concrete poured into concrete formwork built directly over the ground. Slabs that support great structural loads must extend deeper into the earth around their edges, a feature referred to as a footing. The centre, or field, of a structural slab is always thick, typically over 4 inches. Constructing a slab floor generally requires a team of builders; a concrete truck delivers premixed concrete, concrete masons distribute and level the freshly poured concrete and concrete finishers smooth the slab's surface. Once the slab is fully cured, most homeowners choose to cover the surface with tile, laminate flooring or carpet. A growing number of homeowners leave the concrete surface exposed, stamping it with patterns while it's still wet and staining after it's cured. Labor and material combined, the slab on grade floor is relatively expensive. However, concrete is completely pest-resistant and rot-proof.

Dimensional Lumber Joist Floor

The term dimensional lumber refers to the smooth-sided, milled lumber available at hardware stores and lumberyards. The term joist refers to horizontal framing members suspended between opposite walls or beams and covered with decking to form a floor or the structural support for a flat roof. The species of lumber varies according to geographic location; various types of fir, spruce and pine are common. Dimensional lumber joists sit often sit on top of a foundation wall or attach to metal brackets. The joists run parallel to one another and rest at the same vertical level. To complete the floor, builders attach decking, typically plywood, to the top side of the joists. This traditional method of floor construction remains one of the least expensive. However, wood is prone to pest infestation and deterioration. Additionally, heavy footsteps often produce a hollow pounding on joist floors and, if framing nails become loose, the dreaded squeaky floor develops. The lumber joist floor accepts nearly any type of floor covering, including wood floors, tile floors and carpet.

Wood Truss Floor

Whereas the lumber joist is a single, solid piece of lumber, the truss consists of a set of smaller pieces of lumber connected to form a flat-topped and flat-bottomed beam. Between the top and bottom pieces of a truss, supporting pieces form a series of triangles that greatly improve the truss's load bearing strength. Like lumber joists, wood trusses hang between supports, such as walls or structural beams, run parallel to one another and rest at the same vertical level. Trusses are available manufactured to specific dimensions and they generally carry greater loads than a lumber joist. Additionally, trusses weigh less than joists and, because they are connected with metal brackets and selected lumber, they are often less prone to twisting, warping and bowing. Trusses commonly fall somewhere between lumber joists and concrete slabs in price.

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