Laying Out Floor Joists

A floor s framework is made up mostly of wooden joists that run parallel to one another at regular intervals.

Laying out floor joists.

Joists are generally 2 by 8 inch or 2 by 10 inch boards. Use a water management system such as a drip cap or flashing wherever framing meets the home to move moisture away from the home and deck. For most jobs 2 in 5 1 cm x 10 in 25 cm boards are an ideal size. On this deck the extended joists were sistered on the side with the blocks meaning that the new joist layout was offset by 1 1 2 in.

Laying out the rim joist is an optional step and one i have never seen a carpenter do but according to some it does come in handy when you need to check to see that the. Joists are cut to lay flush with the outer surface of the. Attach a header to the sill by standing a board on end so the wider part of the board is perpendicular to the sill. Floor joists are typically 2 by 8s 2 by 10s or 2 by 12s.

Wood joists are structural framing members that are laid upright on edge and nailed equally spaced usually 16 inches on center onto the wall plates. Joists must be level and in plane for a flat surface. It s important to lay out floor joists correctly. This sample table gives minimum floor joist sizes for joists spaced at 16 inches and 24 inches on center o c for 2 grade lumber with 10 pounds per square foot of dead load and 40 pounds of live load which is typical of normal residential construction.

Since the example house we are designing for is 12 feet wide we need to find in the floor joist span table a joist size and centering that can span 12 or wider. Ceiling joists are usually 2 by 6s or sometimes 2 by 4s if it is an older home. Tack a 2x block to the rim joist at the house. Measure the size of the area where you are laying out the floor joists to determine how many joists you need.

Look for high low uneven joists using a tight string line. The rim joist sits vertically on top of the sill plate along the outside of the frame to create a lip for the main floor joists. You ll use the same size lumber to assemble the rim joists as you will for the main floor joists. True floor joist span calculations can only be made by a structural engineer or contractor.

Tack another 2x block to the rim joist over the first beam and then extend a string line that s aligned with the blocks to transfer the layout. The rim joist is not going to help you build the deck floor because you won t trim the deck joist outer ends to an exactly uniform length until all of them are in place. See the image below for an example of joists spaced 16 on center 16 o c. Joists range in size from 2 x 6 to 2 x 12 based on the distance being spanned.

Some newer homes have manufactured i beam shaped joists.