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. Remember to treat the cut ends of pressure-treated wood with a preservative to prevent rot of fungal growth. Provide full-depth 2x blocking between overhanging joists above beam locations. There are, however, many reasons joist bridging is needed for decks. Shall not exceed 592ft2 in deck area [9.12.2.2. Joist blocking spacing at half or third points strengthens the deck frame by improving the connections and distributing forces to more support members. Picture framing and inserts need additional bridging for support and fastening. That said, there are as many blocks to install as there are joists, and if done correctly the job can be efficient and not too time consuming. The height of the deck off the ground may influence whether the joist braces are installed from above or below. Installing supports vertically so the narrow edge is up improves drainage, and minimizes rot potential. Sign up for eletters today and get the latest how-to from Fine Homebuilding, plus special offers. However, we prefer to measure over 1-1/2 in. 5. It unifies the joist framework for a stronger, more cohesive deck. Deck Joist Spacing & Blocking Tips Step 1: Check That Your Deck Frame Is Structurally Sound. Until a few years ago, the IRC didn’t have deck joist span tables. The blocks form a sleeve for the post and provide additional fastening surfaces for bolts. 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. A 16 ft span would require 2 sets of blocking at 5.33 feet from both ends. To ensure the ends of decking are supported, it may be necessary to construct a support frame using blocking. Many carpenters install blocking at the mid-span or 4 to 6-foot intervals. A span is the unsupported distance between two posts. Cutting the blocking at exactly 14-1/2 in. Get complete site access to expert advice, how-to videos, Code Check, and more, plus the print magazine. Attach a rim joist to the end of each joist with (3)10d nails or (3)#10 by 3-inch wood screws. Measure over 1-1/2 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. Many builders will block joists every 4 to 6 feet or at midpoints between supports regardless of joist dimensions. Stringers. Before blocking the last outside joist, run a string line or laser along it. Through-screw the blocking where possible. 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. It is also easier to install blocking for stairs and railing or pergola posts prior to laying down the decking. 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. The layout for straight-line blocking also uses the chalk line, except the blocks are all on the same side of the line. 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. Cutting the blocking at exactly 14-1/2 in. Joists at 12”oc should be spaced 10-1/2”, 16”oc 14-1/2” apart, and 24”oc a 22-1/2” separation. 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. Check fit of the 31/2x31/2 post into the post sleeve prior to attaching it to your deck structure and make any changes to the 31/2x31/2 if needed. Until a few years ago, the IRC didn’t have deck joist span tables. 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. Blocking provides support and strengthens stair-to-deck connections. This does two things. Check Point- … Joists that overlap at a beam should be blocked to prevent twisting, ensure spacing, and transfer compression and flexing stresses between multiple joists. Railing posts fasten to the inside or outside of the rim or end joists. Check periodically to ensure the spacing between joists is accurate. Mark the mid-span on both ends of the deck structure and snap a chalk line across all joists in between. The maximum cantilever allowed—the amount the joist can overhang the beam or post—is 1/4 the total joist span. Cutting blocking is a good way to salvage joists that were rejected for defects. Step 3: Use three 3" quality deck screws for attaching each end of blocking to joist. The extra blocks also can be spaced to improve railing post attachment. spanning 16’-6” between supports may cantilever up to an additional 4’-1 ½” for a total maximum length of 20’ -7 ½” It also allows an in-line installation over the beam or a staggered installation. 11. There is no blocking or bridging between the joists. intervals. 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. (on center) for standard straight composite decking installation. 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. The chalk line should run from one end of the deck to other. Blocking the joists at mid span. Alternating blocking is an easy way to install solid blocking between joists. Take care to make sure that the blocking sits flush with the joist top. It transfers forces between parallel joists and away from rim joists, improving stability. Get tips on joist spacing and blocking requirements so you’re best prepared for installation. Here's a word of caution. Check the blocks to make sure the tops do not extend above the joists, which would create a hump in the decking. The straight-line of joist bridging easily hides beneath a deck board from above and looks better if visible from below. 10. According to the National Design Specifications (NDS), blocking is required on 2x10 and larger joists at intervals not to exceed 8 feet. To prevent nail movement or squeaks, use 2-1/2” spiral or ringed nails. Deck perimeter picture framing requires blocks every 12 or 16 inches between outside joists to support decking laid parallel to the joists. Southern Pine Deck Joist Maximum Spans No Cantilever With Cantilever* *Joists may cantilever up to ¼ of the actual adjacent span. This will result in blocks that are about 1/16 in. 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. Become a member and get unlimited site access, including the Eugene has been a DIY enthusiast for most of his life and loves being creative while inspiring creativity in others. (7)(b)] 3. Some framers prefer to lay the supports horizontally for broader exposure. Most deck builders use scrap or unusable joist boards to cut into blocks for use at mid-span or 8’ spacing between beams. 7. Installing a joist brace between parallel boards helps stiffen the framework and transfer loads between members. Most decking is not strong enough to support longer spans than 16". On the other hand, if approached haphazardly, installing the blocks can take a frustratingly long time. Align the block on the left or right side of the string line mark and flush with the top and bottom of the joist for alternate block placement. I need some advice regarding blocking or bridging to prevent the deck joists from “racking”. The 2018 IRC requires blocking with 2-by material of the same depth as the joists at the open ends of joists to prevent rotation. Blocking, sometimes called crush blocking, is installed to keep the joists upright and to prevent them from rolling to the side under load. The deck bridging may not be structurally required by codes but do improve the firmness or feel of the deck. Install blocking or bridging between joists at mid-span to reduce bounce. off layout. Sight down from above to effectively align the screw. Depending on the porch load, the diameter of the hole will probably range between 8 and 24 inches. To prevent this, cut the blocking at 14-7/16 in. Joist bridging prevents joists from twisting or rotating when under loads or due to moisture-induced … The blocking is placed at the center of the span. 6. Here are the more common ways to block joists. Additionally, we’ll explain several ways to install blocking for different purposes. 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. Ensure all cuts are straight and square. To lay out for the block installation, square up from the beam’s edge inside the last joist. The added material and labor costs make their use questionable. Repeat the same layout process on the other end of the blocking run and snap a line along the joist tops. Blocking makes it easier to construct irregular, semi-circular, or circular decks. To begin, double-check to make sure the space between the joists is a consistent 14-1/2 in. 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. The layout allows direct fastening of one end of the blocks while the other end must be toe nailed into place. Composite decking brands also generally require 12 inches O.C.joist spacing for 45-degree or angled composite deck board applications. To install, align the block to the marks and through-screw (or nail) one end. Here is a list of some common joist sizes and maximum “spans”. Diagonal bracing requires the use of 2×2 material mitered at each end. If the distance is greater than 8 feet, divide the span by three and snap two equally spaced chalk lines. When choosing 2x6 joists, the corresponding ledger board must be a 2x8 minimum. 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. Measure the distance between two joists at the ledger or beam. The joists should be spaced at maximum centres according to the table below. I am calculating the need for 32 pier blocks for a 16x16 deck. The blocks provide support for decking, prevent joists from twisting, and help maintain expanding or unique spacing. The thicker structural screws are more expensive and take longer to drive. You will place the blocking along the chalk lines. 9. A check of local code requirements is recommended to ensure compliance. Cut to the inside of the line. Image Credit: Morris Decks. There’s an easy way to do this. Cut all the blocks at one time. Use the speed square to extend these marks down the face of the beam. The closer the joists are to each other, the greater the distance they're able to span safely. Using a circular saw, cut to the short side of the line, taking the line as you cut. 3. Nail guns are often used by builders, especially where swing space is difficult, as it can be between joists. Joists and Decking Boards. Once the mid or third span bridging is installed, add blocking for picture frames or inserts and post supports.