Blocking provides support and strengthens stair-to-deck connections.The extra blocks also can be spaced to improve railing post attachment. Additional blocking is frequently added between rim or band joists and the joist parallel to it to increase stability and reduce flexing.Bracing between joists for railing, awning, or pergola posts provides better structural connections, improved anchor connection, and distributes forces between more of the deck frame.Joist blocking spacing at half or third points strengthens the deck frame by improving the connections and distributing forces to more support members.Solid blocking with wood the same width and thickness as the joists effectively cross transfers loads between the top and bottom portion or cords of the joists as loads are applied.Bridging between joists reduces lateral movement caused by walking or running across the parallel joists.Blocking midway between support beams strengthens the structure and decreases deflection and bounce by distributing the forces between connected joists.Joist bridging prevents joists from twisting or rotating when under loads or due to moisture-induced expansion or contraction. Joists that overlap at a beam should be blocked to prevent twisting, ensure spacing, and transfer compression and flexing stresses between multiple joists.Blocking floor joists ensure the spacing between joists remains uniform and helps straighten curves or twists.There are, however, many reasons joist bridging is needed for decks. Many carpenters install blocking at the mid-span or 4 to 6-foot intervals. Joists are commonly fastened at the bottom to mid support beams and to deck boards on the top surface, which some consider equivalent to blocking to prevent rotation. Do Deck Joists Need Blocking?īlocking between joists is required under the IRC at the open ends of joists to prevent rotation or every 8 feet if the joist dimensions are greater than 2×12. It should also be noted that preservative chemicals corrode unprotected metal, so use fasteners rated for treated wood. Pro Note: When using pressure-treated wood, remember that all cuts and drill holes exposing untreated wood should be painted with preservatives to reduce rot. Additionally, blocking provides joist braces to support posts for railings and other structures, including stairs. Blocking is also frequently used to create a frame or racetrack to support deck board designs such as picture frames, herringbone, zipper, parquet, and diamond patterns. Most deck builders use scrap or unusable joist boards to cut into blocks for use at mid-span or 8’ spacing between beams. Cutting and installing cross joist braces is time-consuming, requires additional material, and the ends frequently split during fastening, so need to be replaced. Cross bracing joists better distributes the top load from one joist to the bottom of adjacent joists under deflection than strapping or blocking, although blocking is almost as good.
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