Roof Joist Depth

Builders can adjust their choice of lumber size and spacing depending on circumstances.

Roof joist depth.

K series joists range in depth from 10 to 30 and can span up to 60. Flat the most economical flat truss for a roof is provided when the depth of the truss in inches is approximately equal to 7 of the span in inches. Maximum notch depth in the outer third of a joist is one sixth of the joist depth. Do not make square or rectangular cutouts.

These welded steel products are used to support a building s roof and floors. The difference in the joist sizes applies to the width of the boards which determines the height of the ceiling. Considering the cross section of a typical joist the overall depth of the joist is critical in establishing a safe and stable floor or ceiling system. The wider the spacing between the joists the deeper the joist will need to be to limit stress and deflection under load.

Rafter run outer wall this should be measured starting from the center of the roof span and then extending to the very edge of the exterior wall. Here the number is 1166 66 inches. No end notches where the joist is supported greater than 1 4 the joist depth. Limit the length of notches to one third of the joist depth.

No notching in the middle third of a joist. A 2 by 4 inch joist for instance hangs into the room by 4 inches which may leave the ceiling high while a 2 by 12 inch joist in the same position hangs 12 inches into the room which decreases the ceiling height by 8 inches. These joists easily handle spans that wood systems cannot handle while their lightweight construction makes them much less costly than steel beams. The maximum depth of a notch at the end of a joist where it rests on a wall or beam can t exceed one quarter of the joist depth.

Roof rise this should be calculated from the base of the roof to the highest point of the roof gable the peak. No notches deeper than 1 6 the joist depth. The length of a notch should not exceed 1 3 the joist depth. Here the number is 941 86 inches.

Apa performance rated i joists pris are manufactured in accordance with pri 400 performance standard for apa ews i joists form x720 this performance standard provides an easy to use table of allowable spans for applications in residential floor construction allowing designers and builders to select and use i joists from various member manufacturers using just one set of span. 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.