Floor systems consist of framing members fastened together to support live and dead loads of a structure. After the foundation has been placed the framing of a floor system is created. For the purpose of this blog we will only be speaking about timber framing and or light wood construction.
A floor system consists of girders, posts or columns, sill plates, joists, bridging, and subfloor. Girders can be made of solid wood or built up with two or more 2'x material. There are several types of girders; steel beam, laminated veneer lumber or glulam. A girder beam can either be dropped in a pocket within a cement foundation, notched into a wood pile foundation or resting on the sill plate its self. A girder beam will hold the loads of the floor system which is made up of floor joists.
Floor joists are the horizontal framing members that transfer the floor load to the sill plate and girders. The spacing of the floor joists depends on the architectural and engineered plans. Joists can be spaced out either 12" on center, 16" on center, 24" on center, or 19 of diamonds which is 19"3/8 on center. After the joists are laid out and nailed into place a band board is installed also known as the rim board to box off the floor system. Rim boards are typically found in platform construction. Some floor joists have to be dropped into a hanger do to detail specifications on the plans and in this case I always recommend placing a large dab of construction glue on the hanger where the joist sits to prevent a squeak in the floor. Installing floor joists is a fun and exciting task that is not highly difficult if the carpenter studies the house plans and executes the layout properly.
Once the joists are laid and the rim joist is installed the sub floor is put into place. Installing sub floor starts at one corner of the house. To begin, a layout must be accomplished and by snapping a wet chalk line at 4' your ready to begin. It is important to note that a 1/8" space should be allowed between all panels on all sides for an expansion joint. To achieve this I typically use an eight penny nail between sheets of each piece of subfloor to create an expansion joint. While installing remember to use a thick bead of construction subfloor glue and keep an honest and true nailing pattern based on the house plan nailing specifications. After the last piece of subfloor is spaced at an 1/8 of an inch, glued and nailed your ready to layout your exterior and interior walls.