![]() Note that while rule #2 allows a 1 1/2-inch hole in a 2圆, this hole wouldn’t meet the 2-inch edge-clearance requirement of rule #1. In a 2x8, for example, the maximum hole diameter is 2 3/8 inches (actual rather than nominal dimensions should be used to make these calculations). In addition, the diameter of a hole is limited to one-third the depth of the material. To avoid reducing a joist’s bending resistance, no holes can be closer than 2 inches from the top or bottom edges of the joist. There are two limitations to drilling holes in joists. When not required, it's still good practice (see Decay Resistance and the Code, May 2014, PDB).ĭrilling. Also, remember that with some pressure-treated material it may be a requirement of the AWPA standard M4, a required referenced standard of the IRC, for the exposed material in the cut to be field-treated. When cutting notches in the bottom of a joist, try to make angled rather than vertical cuts, which will reduce the likelihood of splitting. Notches allow the pipe to be raised vertically into place. Unlike electrical cable, gas pipe is rigid, and design restraints may preclude sliding the pipe through a series of drilled holes from outside the deck. In a 2x8 joist, for example, notches can be 1 1/4 inches deep, which should allow for recessed gas piping. ![]() These notches can’t be deeper than one-sixth the depth of the joist, nor longer than one-third the depth of the joist. ![]() Notches can also be located anywhere along the top and bottom edges of the joist, as long as the notches are in the outer thirds of the span. This allowance provides useful design flexibility for example, when two different-sized joists bear at the same elevation and still must be flush on the top. This means that a 2x10 can be notched at bearing to the height of a 2x8, yet still get span credit for being a 2x10. If you’re considering laterally bracing the plane of a deck (a common wall-framing practice in the past, when they were sheathed with boards rather than structural panels, and still provided for in the IRC), this means you can’t let the bracing into the joists in the middle third of their span.Ī joist can be notched at bearing locations at either the top or bottom without reducing its structural capability, as long as the notch doesn’t exceed one-fourth the depth of the joist. Since bending forces increase toward the center of a beam and are greatest in the middle third of a span, the IRC prohibits any notches there (see "Joist Notching and Drilling Guidelines," above). Notching involves the removal of material at the top and bottom of the joist, where compression and tension forces are working to resist bending (that is, deflection). Shear stresses increase uniformly from none at all at the center of the span out toward the bearing ends, where they are greatest. Shear acts parallel to the cross-section of the joist and resists the opposing forces of the load and the reaction (the upward force at the bearing point). In addition to being subject to bending stress along their length, joists are also subject to shear stress. If you’ve ever experienced a binding saw blade when cutting the middle of a joist supported at both ends by sawhorses, you know that just the dead load of the lumber itself creates enough compression to pinch the blade in the kerf. These stresses aren’t uniformly distributed throughout the joist instead, they increase from zero at each end to their maximum at the center of the span. When a wood joist that's supported at both ends is loaded, it bends or deflects as it resists the force, pushing the fibers in the top edge of the joist together in compression and pulling the fibers in the bottom edge of the joist apart in tension. When making calculations, use actual rather than nominal dimensions. Avoid notches in the middle third of single-span joists, where bending forces are greatest.
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