For example, a 2 x 12 joist placed 16” OC. The blocks provide support for decking, prevent joists from twisting, and help maintain expanding or unique spacing. But the 2015 IRC included a new one (Table R507.5) that will make it easy for deck builders to spec a joist size for a given span and joist spacing. If the distance is greater than 8 feet, divide the span by three and snap two equally spaced chalk lines. All I am reading is that deck blocks cannot be more than 5ft apart, regardless of the joist size. Some experts question the use of mid-span deck blocking since the joist ends are secure, the top edges fastened to decking, and the bottom to beams which all work to prevent rotation. This means that at one end of the blocking, the screws have to be angled in. Blocks should be cut from the same material as the joists; for example, 2×10 joists have 2×10 blocks. At the first floor joist center point you marked on the beam, measure out and mark 3/4 of an inch in both directions. The thicker structural screws are more expensive and take longer to drive. The use of joist hangers is acceptable for attaching blocking between joists and is even mentioned as an option in my local code; however, their use is uncommon when installing blocking. Cut all the blocking using the same method and at the same time to increase efficiency. shy. Measure the distance between two joists at the ledger or beam. Many carpenters install blocking at the mid-span or 4 to 6-foot intervals. 3a. Building a TimberTech Deck? Cut all the blocks at one time. The blocking is placed at the center of the span. Maximum cantilever of a 2X8 is 24” at 16” o.c. Subsequent blocks will be nailed through a joist at one end and toe nailed at the other end. Railing posts fasten to the inside or outside of the rim or end joists. intervals. Picture framing and inserts need additional bridging for support and fastening. Sight down from above to effectively align the screw. Decks Project Guide. The added material and labor costs make their use questionable. Many local codes identify their use and have set requirements, and Inspectors often look for them. Additionally, blocking provides joist braces to support posts for railings and other structures, including stairs. Lay out the joist hangers on the center beam. To minimize waste and cost, cut blocks from cut-offs or planks unfit for use as joist due to twists or other defects. The nails should be 1-1/2” from the top and bottom edges of the joists and be spaced 2” or more apart, so a 2×8 block should have 2 nails per end. Over the years we have developed a system that gets the job done correctly and quickly. As long as blocking meets this requirement, it does not necessarily have to be centered over the length of the floor joists. According to National Design Specifications (NDS) blocking is required on any deck joist over 8ft long on 2″x 10″ and 2″ x 12″ material. Measure over 1-1/2 in. 1. Using blocks cut from the same material as the joists ensure uniform dimensions and full support from the top to bottom of the joists. Bridging between joists reduces lateral movement caused by walking or running across the parallel joists. Until a few years ago, the IRC didn’t have deck joist span tables. A use of rim or band joist can be substituted for blocking. Most composite and PVC decking brands, like Trex and Azek, recommend a minimum joist spacing of 16 inches OC. A span is the unsupported distance between two posts. 2. Sistering joists to extend a deck is different from sistering a joist to repair or strengthen it. Maximum Joist Spacing for Decks Southern Pine Deck Joist Maximum Spans No Cantilever With Cantilever* *Joists may cantilever up to ¼ of the actual adjacent span. I am building a floating, ground level deck in my back yard. KEEP IN MIND. However, we prefer to measure over 1-1/2 in. Measure the distance between the ledger and beam or beam and beam and divide it by two to determine the halfway point between joist supports. Joists at 12”oc should be spaced 10-1/2”, 16”oc 14-1/2” apart, and 24”oc a 22-1/2” separation. Additional blocking is frequently added between rim or band joists and the joist parallel to it to increase stability and reduce flexing. [9.12.2.2. spanning 16’-6” between supports may cantilever up to an additional 4’-1 ½” for a total maximum length of 20’ -7 ½” I hope you found the guide informative and helpful and have a better understanding of deck bridging. 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. So, when would you ever need to use 12 inches OC? Repeat this step every 3 to 4 feet across the deck. For this situation, the blocking needs to be installed in line to allow the end of the sistered joist to rest on the beam top. Twists, crooks, and rough ends can throw off alignment. Joists that overlap at a beam should be blocked to prevent twisting, ensure spacing, and transfer compression and flexing stresses between multiple joists. Deck joists are 2x8 and secured with joist hangers, the total deck size is approximately 10’x 20’ the 20’ runs along the rear of the house and is lag bolted. In its simplest terms, installing blocking is just filling the gap between two joists. Joist bridging prevents joists from twisting or rotating when under loads or due to moisture-induced expansion or contraction. ft.), but the rim joists carry an area that's the distance between the posts along the rim by half the span the other way (about 8' x 4' = 32 sq. Cutting the blocking at exactly 14-1/2 in. If using tracks or joist caps either lower the blocks below the upper edge of the joist by 1/2″ or trim the blocks to be flush with the bottom of the joist. The straight-line of joist bridging easily hides beneath a deck board from above and looks better if visible from below. Many builders add deck blocks between all joist dimensions at mid-beam spans or spacing every 8 feet, whichever is less, to prevent bounce and sway. It is also a good cost-saving use of joist scraps and unusable twisted or bowed joist timbers. Additionally, the ends often split when fastening into place which requires the use of a new piece. Deck boards commonly run perpendicular or diagonally to the joists. Nail guns are often used by builders, especially where swing space is difficult, as it can be between joists. Protect horizontal surfaces with a moisture barrier for the same reason. Joist span length and spacing is a function of joist size—the requirements are presented in IRC Table R507.5. This does two things. This line represents one side of the blocking; it can be used to reference the blocking installation by setting all the blocking to the inside of the line. Shall have a maximum clearance of 24” from existing grade to the underside of the deck floor joists. The maximum cantilever allowed—the amount the joist can overhang the beam or post—is 1/4 the total joist span. Depending on the porch load, the diameter of the hole will probably range between 8 and 24 inches. Composite Deck Joist Space. Installing blocking is easier to do prior to the laying down of the decking. If necessary, trim any blocking that sits proud; otherwise, it will create a bump in the decking. If you are using a chopsaw, be aware that most chopsaw blades are thicker than a hand-held circular saw and your blocks may end up too short. Cantilevering. Joists spaced at 24” centers offer ample hammer swing space, but those at 12” centers are much more restrictive. Become a member and get instant access to thousands of videos, how-tos, tool reviews, and design features. Measure where the blocks are needed at both ends of the deck and snap a chalk line. Provide full-depth 2x blocking between overhanging joists above beam locations. The majority of composite deck board brands including Trex, TimberTech, and more require deck joists spacing to be at 16 inches … Start your subscription today and save up to 52%. Most decks use 16" on center spacing for joists. Alternating blocking is an easy way to install solid blocking between joists. To protect the wood and your investment use bituminous adhesive tape, tar paper strips, or flashing on horizontal framing surfaces. Hundreds of articles and videos by top deck-building pros on how to design and build a beautiful, sturdy, and safe deck. Check Point- … Many builders will block joists every 4 to 6 feet or at midpoints between supports regardless of joist dimensions. What is Joist Blocking in Deck Construction? The IRC also requires blocking or the use of 1×3 strapping every 8 feet or less between joists of greater than 2×12 dimensions. Drawing cut lines using a square helps for straight square cuts. It also helps to share any additional stress forces – such as the semicircular feature. The extra blocks also can be spaced to improve railing post attachment. 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. Step 2: Run String Lines to Ensure All Joists Are Level & In Plane. The use of flashing, tarpaper, or bituminous tape helps protect surfaces from rot. The maximum cantilever length is determined by the lesser of one-fourth of the joist span or the maximum cantilever length shown in MRC Table 507.6. and mark a crow’s foot to reference the chalkline. Stringers. That seems excessive. Many deck framers will measure so that the staggered line of blocks falls under a deck board to protect them from moisture and make them invisible from above. Outside joists may not be spaced at 16”oc or may need to adjust to get the proper fit for decking. Moisture trapped, or sitting on wood will lead to rot and structural damage. Repeat the same layout process on the other end of the blocking run and snap a line along the joist tops. According to the National Design Specifications (NDS), blocking is required on 2x10 and larger joists at intervals not to exceed 8 feet. The NDS also requires blocking between end joists or the use of rim or band boards to prevent rotation. In really tight spots a palm hammer is helpful. The NDS requires 2-by blocking every 8’ or less for 2×10 and 2×12 joists. Cutting the blocking at exactly 14-1/2 in. Some builders use specially designed and manufactured structural screws instead of nails to pull twisted joists against the blocks and to prevent squeaks. The nails are driven through the joists into the ends of the blocks. 2. Here is a list of some common joist sizes and maximum “spans”. It is acceptable to cantilever joists beyond the end support beam depending on the type and grade of wood, the plank dimensions, and the joist spacing. Remember to treat the cut ends of pressure-treated wood with a preservative to prevent rot of fungal growth. To ensure the ends of decking are supported, it may be necessary to construct a support frame using blocking. long, or thereabouts. Joists are the wood beams arranged in a parallel pattern to support the deck's overlying structure. Mark a board at 14-1/2-in. The benefits of mid-beam joist span deck blocking are felt in the structural stability of most decks. Cut to the inside of the line. For instance, joists that are placed 24 inches apart must be wider than joists placed 16 inches apart. Leaving the required 1.5” spacing for surface fastening at the end of the board and 1” from the side of the board, requires two joists … Take care to make sure that the blocking sits flush with the joist top. Predrilling solves the splitting problem but increases the cost and installation time. The plan for this deck called for more joists to be sistered on at the beam. A check of local code requirements is recommended to ensure compliance. The required width of a joist depends on its span: how far it must travel between beams or between a beam and a ledger. For example, a 2 x 12 joist placed 16” OC. Deck bridging provides support for picture frames and other deck board designs such as diamonds, herringbone, or parquet while allowing moisture to pass through. Here are the more common ways to block joists. A 2x6 will span less than a 2x8 and so on. Blocking midway between support beams strengthens the structure and decreases deflection and bounce by distributing the forces between connected joists. In this guide, we’ll discuss what joist blocking is and why it is necessary, plus requirements, methods, and spacing. Some brands, like WearDeck, let you get away with more – reinforced with a layer of fiberglass on both the top and bottom, WearDeck boards easily allow for spans of 24 inches OC. Some builders reduce joist spacing to 12" on center to strengthen the deck frame or to increase maximum allowable joist spans. Repeat this step every 3 to 4 feet across the deck. Deck perimeter picture framing requires blocks every 12 or 16 inches between outside joists to support decking laid parallel to the joists. Before blocking the last outside joist, run a string line or laser along it. Blocking floor joists ensure the spacing between joists remains uniform and helps straighten curves or twists. 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