Anatomy of Your Wood Frame Floor

  • Beginner

Your home's wood frame floor includes many parts that add both to the stability of your home and to your comfort. Learn more below about such wood-frame floor parts as joists, subfloors, underlay, and the best adhesives to use for specific floor coverings.

Live and Dead Load

The floor and walls of your home support weight known as a live load or dead load. The live loads are the temporary loads that don't get attached permanently to the structure such as the furniture and the appliances you bring into the house when you move in. The weight of the structure itself or from any permanent attachments and fixtures such as drywall, roof sheathing, trusses, plumbing, pipes, ventilation system, floor coverings... etc, is what is referred to as the dead loads.

Floor Joists

The floor joists are the horizontal beams that make up the floor frame grid onto which the subfloor is to be fastened. The joists grid must be built strong enough to carry every piece of structural lumber and other framing added above that floor level and everything else sitting on that floor including the weight of every subsequent floor and what's on them. They are made from 2-inch by 8-inch solid lumber or wider and are normally spaced 16 inches apart at their centers. Both ends of each floor joist are fastened into and supported by load-bearing walls or vertical support posts.

Supporting Posts

The posts that support the joists may be made of solid wood or they may be steel.


Typically made of plywood or OSB and ranging in thickness from 19/32" to 1 1/8" thick, the subfloor is mainly structural, sitting directly onto the joists. Most building codes require that this subfloor be at least 5/8 inch thick. In a home built on a concrete slab with no open foundation or crawlspace, the subfloor is solid poured concrete.


Underlayment is necessary for carpeting, laminate flooring, and some kinds of hardwood floors. The underlayment helps trap moisture that can cause mold growth in carpets and can warp wood floor paneling. Underlays with an aluminum vapor barrier can help stabilize and level an uneven subfloor surface. Specialized underlays have been developed to provide improved heat transfer and protection for floor surfaces installed over heated flooring systems. Other underlays insulate floors and reduce the transmission of sound. You might want to install these underlays in second-floor bedrooms to make them quieter for sleeping.

Flooring Adhesives

The kind of flooring adhesive used will depend on the type of flooring you install above it. Use a solvent-based or urethane adhesive under a hardwood panel floor, a parquet floor, or an engineered wood floor to prevent moisture seepage into the wood. Use a water-based low emission adhesive to secure the carpet to a plywood subfloor. New types of heat-resistant adhesives have been created to add floor surfaces to heated floors. Ensure the subfloor surface is clean and level before applying adhesive for any floor covering.

Floor Coverings

From ceramic or terracotta tile to hardwoods in a range of types, your floor coverings will help unify and define the style of your home. Install durable floor coverings, such as tile or laminate, in areas where people walk most often and where spills may occur, such as the kitchen. Choose a soft and invitingly textured floor covering, such as carpeting or area rugs over hardwood, for family rooms and bedrooms.

Why You Need to Know About Your Wood Frame Floor

If you decide to install heavy furnishings in your homes, such as encyclopedia bookcases or a 20-gallon aquarium, you need to know if your floor can support this concentrated weight.