Snap a chalk line across the center of your joists to lay out your bridging. To begin, double-check to make sure the space between the joists is a consistent 14-1/2 in. 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. 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. The deck bridging may not be structurally required by codes but do improve the firmness or feel of the deck. 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. You will place the blocking along the chalk lines. A good rule of thumb is to think if the distance between any two rows with blocking is more than eight feet, you must add some more blocking there. On BestDeckSite, we recommend installing blocking on 2x8 joists too. Become a member and get unlimited site access, including the Blocking, sometimes called crush blocking, is installed to keep the joists upright and to prevent them from rolling to the side under load. Angle the screws to secure the blocking where necessary. Alternating blocking is an easy way to install solid blocking between joists. Predrilling solves the splitting problem but increases the cost and installation time. This will result in blocks that are about 1/16 in. Starting near the end of the deck, snap a chalk line perpendicular to the joists. 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. I am building a floating, ground level deck in my back yard. Check for protruding nails and screws. 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. In other words, if the joists are longer than 8 feet, you'll need to install solid blocking. A deck is an extension of the living space and should be a solid platform for your outdoor activities. Additionally, the ends often split when fastening into place which requires the use of a new piece. We would recommend blocking on any deck joists greater than 2″ x 6″. A use of rim or band joist can be substituted for blocking. A band or rim joist, or a header are acceptable alternatives to end blocking. Check periodically to ensure the spacing between joists is accurate. Bridging between joists reduces lateral movement caused by walking or running across the parallel joists. Each of the regular joists carry an area that's equal to their length by the joist spacing (about 1'-4" x 8' = 10.66 sq. Depending on the porch load, the diameter of the hole will probably range between 8 and 24 inches. The NDS requires 2-by blocking every 8’ or less for 2×10 and 2×12 joists. 3a. Composite decking brands also generally require 12 inches O.C.joist spacing for 45-degree or angled composite deck board applications. and mark a crow’s foot to reference the chalkline. It also depends on the joist spacing. The majority of composite deck board brands including Trex, TimberTech, and more require deck joists spacing to be at 16 inches … The extra blocks also can be spaced to improve railing post attachment. 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. shy. Take care to make sure that the blocking sits flush with the joist top. intervals. What is Joist Blocking in Deck Construction? Attach a continuous rim joist or blocking at the joist end as shown in Figures 3, 5, and 7. 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. To ensure the ends of decking are supported, it may be necessary to construct a support frame using blocking. It is also a good cost-saving use of joist scraps and unusable twisted or bowed joist timbers. long, or thereabouts. Installing supports vertically so the narrow edge is up improves drainage, and minimizes rot potential. spanning 16’-6” between supports may cantilever up to … The Joist span table below is for joists with a continuous span on a deck below 1metre in height. 9. Blocking floor joists ensure the spacing between joists remains uniform and helps straighten curves or twists. This means that at one end of the blocking, the screws have to be angled in. Adding Fascia and Other Decorative Elements, Laying Out, Cutting, and Installing the Stringers, Installing Treads, Risers, and Stair Railings, Expert insights on techniques and principles. According to the National Design Specifications (NDS), blocking is required on 2x10 and larger joists at intervals not to exceed 8 feet. Decks get wet and may be framed with incised treated lumber so spans may have to be adjusted. This does two things. Deck joists require a minimum of 1-1/2 inches of bearing on wood and 3 inches on concrete. I am calculating the need for 32 pier blocks for a 16x16 deck. Maximum 16'-6 "span for solid stringer (southern pine) Maximum 7'-0 … Protect horizontal surfaces with a moisture barrier for the same reason. off layout. There are, however, many reasons joist bridging is needed for decks. Measure and mark an entire board at 14-1/2-in. 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. If necessary, mark a square line across the board face to align the sawblade as you cut. It may necessitate lowering the blocking below the joist edge by 1-1/2” and laying a 2×4 flat on the blocking. Builders frequently have a preference when it comes to installing blocks based on experience, costs of material and labor, maximum effect, and code compliance. Many local codes identify their use and have set requirements, and Inspectors often look for them. When using surface fasteners to secure railing to a composite deck, joist location may affect the ease, price and method of the installation of the railing system. Joist blocking spacing at half or third points strengthens the deck frame by improving the connections and distributing forces to more support members. Mark a board at 14-1/2-in. Cut blocks for inside joists all to the same length, 14½ inches. 3b. Blocking creates a sleeve for the railing post and additional fastening material. Blocking makes it easier to construct irregular, semi-circular, or circular decks. The chalk line should run from one end of the deck to other. You can sight down the face of the block and beam as well as align the edge to the line. In its simplest terms, installing blocking is just filling the gap between two joists. However, we prefer to measure over 1-1/2 in. Blocking is a common technique that involves putting small pieces of decking material between joists to increase rigidity and prevent them from twisting or sagging. 12. 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. The tracks or protective joist caps are an alternative to bituminous tape, tar paper strips, or flashing. 4. 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. Lay out the joist hangers on the center beam. Sign up for eletters today and get the latest how-to from Fine Homebuilding, plus special offers. Diagonal bracing requires the use of 2×2 material mitered at each end. The plan for this deck called for more joists to be sistered on at the beam. Cutting the blocking at exactly 14-1/2 in. But shouldn't that matter? Where blocking between joists is required, attach blocking using joist hangers at each end or by toe- nailing blocking to joists at each end, top and bottom with 10d nails. So, the what and the why affect how. Do not notch 31/2x31/2 railing posts. 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. 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. For example, a 2 x 12 joist placed 16” OC. The blocks alternate on the left or right of the string marking. Stringers. The NDS also requires blocking between end joists or the use of rim or band boards to prevent rotation. (7)(b)] 3. nailing blocking to joists at each end, top and bottom with 10d nails. To fasten deck blocking 10d nails are commonly used. 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. You will place the blocking along the chalk lines. See the deck joist calculations below and study your local code. 7. Using blocks cut from the same material as the joists ensure uniform dimensions and full support from the top to bottom of the joists. The maximum cantilever allowed—the amount the joist can overhang the beam or post—is 1/4 the total joist span. In this guide, we’ll discuss what joist blocking is and why it is necessary, plus requirements, methods, and spacing. At the first floor joist center point you marked on the beam, measure out and mark 3/4 of an inch in both directions. Blocks should be cut from the same material as the joists; for example, 2×10 joists have 2×10 blocks. Joist spacing is limited by the span rating of the decking being used, see MRC Table R507.7. 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. ICC Digital Codes is the largest provider of model codes, custom codes and standards used worldwide to construct safe, sustainable, affordable and resilient structures. We would recommend blocking on any deck joists greater than 2″ x 6″. The nails are driven through the joists into the ends of the blocks. Through-screw the blocking where possible. To install, align the block to the marks and through-screw (or nail) one end. Leave outside joists for last and install blocking from underneath. Once the mid or third span bridging is installed, add blocking for picture frames or inserts and post supports. Shall not exceed 592ft2 in deck area [ Joist span length and spacing is a function of joist size—the requirements are presented in IRC Table R507.5. On the other hand, if approached haphazardly, installing the blocks can take a frustratingly long time. Some extra pieces may be required to support deck board ends at posts too depending on board runs. The closer the joists are to each other, the greater the distance they're able to span safely. When choosing 2x6 joists, the corresponding ledger board must be a 2x8 minimum. to mark the location of the line to which the blocks will be aligned. 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. Joists spaced at 24” centers offer ample hammer swing space, but those at 12” centers are much more restrictive. Nail guns are often used by builders, especially where swing space is difficult, as it can be between joists. 11. Many carpenters install blocking at the mid-span or 4 to 6-foot intervals. The first block will be nailed through parallel joists into each block end. To minimize waste and cost, cut blocks from cut-offs or planks unfit for use as joist due to twists or other defects. As long as blocking meets this requirement, it does not necessarily have to be centered over the length of the floor joists. Treat the ends of the blocks with wood preservative and set them aside to let the preservative dry before installing. An easy deterrent or fix is the use of deck joist blocking. 1. Repeat this step every 3 to 4 feet across the deck. 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. The blocking is placed at the center of the span. post spacing is 6' to the center of each post. 2. Most decks use 16" on center spacing for joists. 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. Standard screws or deck screws are not recommended for structural use as they can snap due to stress forces. Install blocking along the perimeter rim joists to strengthen guardrails. Hundreds of articles and videos by top deck-building pros on how to design and build a beautiful, sturdy, and safe deck. Joists at 12”oc should be spaced 10-1/2”, 16”oc 14-1/2” apart, and 24”oc a 22-1/2” separation. Cut all the blocks at one time. A 16 ft span would require 2 sets of blocking at 5.33 feet from both ends. They also improve post stability and transfer forces against the top of the post or railings away from the rim or band joists. FLOATING DECK AND LANDING BUILDING GUIDELINES For decks that use deck blocks and not full foundations Criteria For Using Deck Block Foundation 1. Nails have greater shear strength and screws greater pulling and holding ability. Most builders, though, recognize that blocking every 4 to 6 feet unifies the frame and improves structural strength. The layout for straight-line blocking also uses the chalk line, except the blocks are all on the same side of the line. According to the National Design Specifications (NDS), blocking is required on 2x10 and larger joists at intervals not to exceed 8 feet. A wobbly or bouncy deck is a cause for concern and doesn’t instill confidence in the skills of the builder. This will leave you with blocking that is 14-7/16 in. If you found the guide useful, please share it with others. Attach a rim joist to the end of each joist with (3)10d nails or (3)#10 by 3-inch wood screws. The guide will provide you with all the information you need for blocking deck joists. The blocking is placed at the center of the span. Subsequent blocks will be nailed through a joist at one end and toe nailed at the other end. Joists are the wood beams arranged in a parallel pattern to support the deck's overlying structure. Decks get wet and may be framed with incised treated lumber so spans may have to be adjusted. The thicker structural screws are more expensive and take longer to drive. Blocking can be done along the perimeter of the frame, mid-span, or both. 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. Additional pieces of joist material or smaller dimension lumber may be cut with mitered ends to fit between joists and square-cut blocks to form a framework to support inserts or frames. Check the blade thickness. 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. Maximum cantilever of a 2X8 is 24” at 16” o.c. Although only required at the open joist ends or for larger dimension joists, many builders block all joists every 4’ to 6’ or mid-span regardless of joist size. It provides a more solid structure by reducing the sway and bounce by sharing the forces across the joist bridging. Additionally, we’ll explain several ways to install blocking for different purposes. Image Credit: Morris Decks. The benefits of mid-beam joist span deck blocking are felt in the structural stability of most decks. I hope you found the guide informative and helpful and have a better understanding of deck bridging. A 16 ft span would require 2 sets of blocking at 5.33 feet from both ends. It also helps to share any additional stress forces – such as the semicircular feature. Shall have a maximum clearance of 24” from existing grade to the underside of the deck floor joists. It should also be noted that preservative chemicals corrode unprotected metal, so use fasteners rated for treated wood. There is no blocking or bridging between the joists. Deck joist blocking and bridging at mid-beam span or intervals less than 8 feet decreases bounce and sway. Deck joist blocking is pieces of wood cut from joist material and installed perpendicular to the joist to connect or bridge the gap between joists. Additional blocking every 8’ or less is also mandated for joists larger than 2×12. Mark the joist at the other end in the same manner and snap a chalkline along the joist tops. In other words, the distance between any two rows of blocking, or any one row of blocking and the end of the deck, cannot be more than 8 feet. Outside joists may not be spaced at 16”oc or may need to adjust to get the proper fit for decking. To begin, double-check to make sure the space between the joists is a consistent 14-1/2 in. 5. Joists … Blocking 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. Additional blocking is frequently added between rim or band joists and the joist parallel to it to increase stability and reduce flexing. Use a square to mark the joist face where it intersects the beam face. 10. To determine the correct joist required, we need to establish the spacing of our joists. Small sections of joist material can be installed between the joists as mid-span blocking to help prevent deck bounce and strengthen through-the-deck rail post attachments. Drawing cut lines using a square helps for straight square cuts. The required width of a joist depends on its span: how far it must travel between beams or between a beam and a ledger. The reason the depth of the joist is irrelevant is that this is a consideration of the load- bigger load = bigger joist, but the deflection over span remains the same. 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. If there will be heavy objects like a hot tub or built-in planters, extra blocking will help spread the additional load to other supports. 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. Step 3: Use three 3" quality deck screws for attaching each end of blocking to joist. 4. 7. Measure where the blocks are needed at both ends of the deck and snap a chalk line. The American Wood Council’s 2015 edition of the National Design Specifications (NDS) requires 2×10 and 2×12 joists to be blocked at intervals of 8 feet or less. Measure and cut the blocks from the same material as the joists. Installing a joist brace between parallel boards helps stiffen the framework and transfer loads between members. This aligns the joists with perfect spacing. This is just as strong as running them straight in but takes a little more time. (7)(c)] 2. Deck bridging provides support for picture frames and other deck board designs such as diamonds, herringbone, or parquet while allowing moisture to pass through. Cantilevering. Step 2: Use blocking that is the same size and dimension as the joist members to reinforce the side of the 31/2x31/2 post opposite the rim joist. Blocks should be flush with the top and bottom of the joists at mid-beam span or 8 feet, whichever is less. Stylized designs often have deck boards running parallel to joists. Seems like I can cut this amount down using 2x8s. Building a TimberTech Deck? 3. The blocks are commonly uniform in length, being 14-1/2” for joists spaced at 16” centers, 10-1/2” for 12” centers, and 22-1/2” for 24” centers. Additionally, the space between the joists can affect the install. 8. Here is a list of some common joist sizes and maximum “spans”. Deck joist spacing for composite decking remains largely the same as if working with treated lumber. To prevent this, cut the blocking at 14-7/16 in. The 2018 International Building Code (IRC) Section 502.7 requires deck joists to be blocked with 2-by material the same depth as the joists at the ends to prevent rotation. To protect the wood and your investment use bituminous adhesive tape, tar paper strips, or flashing on horizontal framing surfaces.