Factors that Determine Deck Joist Spacing and Span. By the time you’re finished reading this guide, you’ll have a better understanding of how span and spacing work, and what will structurally work best for your deck. That affects the joist and beam directions, as well as the live load requirements. Remember to follow local code for deck posts. It also determines if joists will be cantilevered which also affects the span and spacing. Finally, it will list various joist lengths, such as 6’, 8’, 10’, and so on. Windows, trees, neighbors, and utilities are other factors to keep in mind. The formulas have been used to calculate the spans and spacing on different tables in the Building Codes, and are the values used by different calculator algorithms. Deck Brighteners contain oxalic acid, which will also remove tannins. What they do tell you is the maximum length of a beam for a particular joist span. The type of decking selected may require special fasteners and tools too. On the flipside, a post will touch the deck every time it’s used, providing a steady support system. Decking may be perpendicular or diagonal to joists, full run or staggered, or something unique. Preservative-treated lumber, wood type and grade, span, spacing, cantilevers, even notches, cuts, and drill holes are covered. Having long joists is nice because, in theory, it could mean a shorter beam. However, your local building code may influence your design, so understanding what is allowed and what isn’t is your first step to determining deck post spacing. It is better to go shorter than to try and maximize span bridging for a more solid and secure platform. However, be mindful of the size – do you want a house with a deck or a deck with a house? It offers greater strength and allows joists to be spaced up to 24”o.c. Some jurisdictions do not allow bracing on a middle post if you have one. If you look at the deck post spacing chart below, you’ll notice that the higher the post, the shorter the beam span it can support. It also improves the structural strength of the deck. On the other hand, you can always fabricate a larger deck beam and put your deck support posts further apart. For those in Canada, many consider tables from Ontario and deck support post information found in tables from British Columbia are helpful. Although 2x4s may be used for low-profile joists near ground-level they aren’t normally included in structural joist tables. Lumber grades further identify the strength of different wood. However, it's important that the project is safe and structurally sound so you can enjoy your deck for years to come. The joists may be cantilevered at each end beam or terminate flush with the end beams. Joists commonly are spaced at 12”, 16”, or 24” centers depending on the load the deck frame will carry and the size, type, and orientation of the deck boards. 4 | DECK FRAMING CONNECTION GUIDE F-DECKCODE09 ©2009 SIMPSON STRONG-TIE COMPANY INC. Railing Post-to-Deck Framing (page 15) Lateral Load Connection (page 9) Ledger Attachment (page 8) Stair Tread-to-Stringer (page 16) Joist-to-Ledger when perpendicular to joists. joist spacing increases material cost between $70 for 2x8s and $100 for 2x10s. A larger beam can span a greater distance, requiring fewer but larger footings. Every municipal code is slightly different and you want to base your final calculations on your local code – not an online calculator. Installing deck railing is easy if you use an anchored handrail system. It’s best to adhere to the Code or involve a Structural Engineer. A quick rule of thumb for determining joist thickness for 12”o.c. A beam of that size can span nearly 12’ while supporting 10’ joists. Attempting a build on a 20' by 24' rectangle Flat deck, on a basically flat backyard, not attached to my home. Joists that cantilever allow for the use of longer joists than those that terminate at the outside face of the beam. for boards laid at an angle to the joists. It varies because decks come in so many different sizes and shapes. The cost difference between 2x8s and 2x10s is approximately $7.00 each. The greater the load, the larger the footing dimensions. Living in a region with heavy snow loads or winds can also increase the live load values, and so should be included in the design considerations when building a deck. The local Building Code is adapted from the State or National Building Code, which in turn is based on the International Residential Building Code (IRC). Deck Board Spacing. You'll need the post layout marked before you begin. Most 2” thick wood planks are fine traversing joist spacing of 12”o.c., 16”o.c. For example, a three-ply 2×8 support beam will span nearly 2’ longer than a two-ply 2×8 beam for joists of 12’. When using a two-ply deck beam atop 4x4s, you are limited in terms of how far you can space your deck support posts. Joist size determines span and spacing, so select the grade and type of wood best suited for your needs and budget. The height of your deck actually can determine how many deck posts you will need. Factors that Determine Deck Joist Spacing and Span, How to Determine the Proper Deck Joist Sizing and Spacing, 4. Codes address all aspects of residential construction, not just decks. The most obvious factor is how your deck is laid out and the type of space it occupies. Use 6×6 deck support posts and an 8” or 10” wide 3-ply beam. Placing the beam so the outside face is 12’ from the structure or 10’-6” doesn’t affect the cost, but does impact the structural strength. Eugene has been a DIY enthusiast for most of his life and loves being creative while inspiring creativity in others. Low profile free-standing decks or ledger supported decks fasten to the beams using joist hangers. REMEMBER THESE THINGS. A deck is an outdoor living area and enhances the look and character of a home. 6×6 support posts require a minimum of 10” diameter footings. The width, thickness, wood type, grade, and spacing influence the span a joist can bridge. The more elaborate the decking plan, the greater the joist structure requirements. or 16”o.c. 12”o.c. In most cases, it’s best to start with a full board on the outside edge of the deck and … I am looking to install privacy screens on my concrete patio. Because the maximum span a two-ply 2×12 can run is just over 9’. Unfortunately, if you step down to a three-ply 2×10, you would still need 3 deck support posts because a beam of that size spans just under 10’. Uncovered Decks and Porches How to Use this Guide Provide two sets of plans, drawn to scale and complete the following (hint: use graph ... posts spaced apart (example: 4 x 4 posts spaced 8’ apart) ... post locations and spacing, joist and beam spans, and any other pertinent information not shown on the section drawing. If your deck is more than 2’ high, your corner support posts will need to be braced parallel and perpendicular to the support beam and deck joists, respectively. 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. Deck boards that diagonally cross joists at angles such as 30°, 45°, or 60° span a greater distance, and so the deck joist spacing must be adjusted. Incising weakens the wood slightly, so it often is rated for shorter distances. The spacing reduces to 12”o.c. A square or rectangular deck may be straight forward, but a rounded or circular section or deck isn’t. 4×4 deck support posts cannot be used if a deck is more than 5’ off the ground. 4. A 2×6 yellow pine at 12”o.c. Minimum 36 ”at all points above the permitted handrail height. Joist Span – Joists Attached at House and to Side of Beam. Generally, the maximum joist spacing for boards running perpendicular to the joists is 16”o.c. Cut the Posts. ), and the height off the ground. A structurally solid and safe deck is the end product of all the building components, even if all that is seen and admired are the deck boards. The planks are nominally 6” x 5/4” and usually spaced 1/8” to 3/8” apart. That leaves one beam to be supported by two or more posts. There are several methods for setting posts. Check out our table below which is based on the information on Table R507.5 of the 2018 IRC. Local building codes address unique conditions for their specific region, including the load-bearing ability of soil, frost and seismic issues, plus snow and wind load concerns. It is important to note that not all values in some tables are the same as what is in the IRC, so it is important to check the local Code for accurate current values for your area. Lower grades, economy, or utility lumber have too many knots or large knots that weaken the lumber too much for structural use. Therefore, if you want to minimize the amount of deck support posts, go 6×6 instead. One way is to pour concrete in the post hole, set the post on the concrete and backfill with gravel. Joist installation doesn’t impact the spacing between joists, but it does affect the span. With this information you can apply for any permits needed. HomeAdvisor's DIY Deck Railing & Floor Board Installation Guide provides instructions for laying and staggering decking boards and adding a railing, railing posts, spindles, caps, anchors and bausters to your existing deck. Downsizing to 16”o.c. The frost line and snow load tables in Florida are different than Minnesota, so code has to take that into account, for example. The joists are fastened to the beams to maintain spacing and prevent movement. and 16”o.c. The narrower the spacing between joists, the greater the span can be. 2×6 deck boards can span up to 24”o.c. Deck Support Column Design . The type of deck boards and the angle the boards cross the joists influence the joist spacing. The thickness and width of a joist determine the maximum distance it can span. When planning a deck, consider the direction the deck boards are to go. Stringer spacing for stair treads is commonly 12”o.c., although some products are 16”, 11”, or 8”, so it is best to check the instructions. The span between beam supports (6’) multiplied by the joist span plus any cantilever (12’) identifies the “Tributary Area” (72sqft) of the deck which is used to determine the allowable beam post height and footing size. Most decks have joists that are attached to a ledger board, which is affixed to the house. Additionally, the inconsistent spacing will create an irregular pattern of fasteners that detracts from the visual look of the deck. and 24”o.c. Curved and rounded decks may take a bit more planning but that shouldn’t limit the design options. The most common grade used for joists and deck framing is #2, which has some knots but not enough to weaken it. Building a deck involves multiple carefully planned steps. Determine the basic design of the deck, such as posts, beams and other spacing, and prepare a materials list. On the other hand, as your joist length increases, so does the diameter of your footings that your deck support posts sit on. Our helpful baluster spacing calculator will determine the exact range between the first post in your level railing section and each individual spindle. the span maximum is 9’-1”. Your comments and suggestions are always appreciated. All are common methods and may affect the overall design and cost of the project. Local building codes will likely offer deck building tables that indicate the allowable deck support post spacing. Another issue is joist spacing. The maximum span indicates how long a beam can run supported by two deck support posts. The drawback when using 4x4s is that you cannot use a three-ply beam – it won’t fit on top of the 4×4. Deck joist spacing for composite decking is the same as that for 5/4” boards. While these online calculators are great for visualizing what your deck might look like in terms of where you place your deck support posts, keep in mind that they are only an estimate. Spacing the balusters. If you can’t find any of their information online, just call or, even better, go in person. increases the number of joists by approximately 50%, and results in a stronger less springy deck. A span is the unsupported distance between two posts. The grade, wood type, spacing, thickness, and width determine the distance joists can safely bridge. Spacing may be less, but shouldn’t be more. A hot tub may be part of the purpose but it affects the shape and size of the deck too. The last columns identify the spans for the beam at 12’ and 10’-6” with the cantilever. Learn how much spacing should go between handrail posts and how to install boards and railing for corner decks. The tributary load is the load carried by any one post in your deck. The IRC reflects proven construction techniques for wood decks using widely accepted conventional construction materials and practices. Each factor affects the span, the spacing, or both, as well as the placement of beams and support posts that make up the deck frame. There are tons of spacing charts available online, made available by various municipalities to help their constituents better understand how to properly space their deck support posts to ensure they pass inspection. I will attach 2 x 6 or 2 x 8 deck joists to these posts. The shape often determines the direction of the joist grid, which in turn affects the deck board layout and direction. Different types of wood, even within species, have different physical characteristics and strengths. Most span and spacing tables present values for common dimensional lumber sizes and species. The 2018 IRC is a good place to start as is your local Code which may adjust values or loads for regional conditions. He is passionately interested in home improvement, renovation and woodworking. The spacing between joists is 12”o.c. Many reflect the information found in the IRC or National Building Codes. Another way for 16”o.c. STAIRS. However, if you opt to space your joists only 12” on center you can have a much longer deck span – up to 2’ longer. Pressure-treated lumber is protected from moisture and insect damage, as well as mold and mildew. spacing. I hope you’ve found it helpful and are now confident enough to plan and space your deck support posts! Many composite decking brands and all 5/4” wood boards are limited to 12”o.c. Common in my area is pressure-treated SPF, cedar, and several brands of composite deck boards. One of these tables will first indicate the wood type – typically SYP (Southern Yellow Pine) or SPF (Spruce Pine Fir). or less if the decking is laid perpendicular, or 12”o.c. High Strength: Douglas fir and southern yellow pine will span greater distances. Never take one municipality code to be the rule – code varies drastically depending on your geography. PRESCRIPTIVE RESIDENTIAL WOOD DECK CONSTRUCTION GUIDE 5 American Wood Council Figure 1B. It is also less expensive than select or #1 grade wood. Then it will list all the different beam types, such as 2 – 2×8, etc. Most residential decks are designed for loads of up to 10 people and a live load of 40psf, whereas commercial decks must meet live loads of 100psf or more. Luckily, there are tons of handy charts to help get you started. Free-standing decks don’t have a ledger. Check out the calculator below. R507.2.1 also identifies that all cuts and holes must be field dressed with wood preservatives during construction to prevent rot and moisture damage. The dead load is the weight of all the building materials and is commonly calculated at 10psf. Each factor affects the span, the spacing, or both, as well as the placement of beams and support posts that make up the deck frame. The overall load is made up of the dead load and the live load. Square or rectangular decks are easier to layout a joist and beam plan for. To show how the joist spacing, span, and sizing interact, here are several examples based on a 12×12 deck. The Building Code stipulates acceptable spacing to prevent injury or death due to improper spacing which can cause structural failure. Once you have your joist span, and pier spacing you can size each component of the deck using Tables 1 and 2 below. One of the biggest is knowing what your local building code allows. A 2×6 yellow pine at 16”o.c. and 16”o.c. joist spacing. 2. Lumber with no blemishes is rated select, clear, or #1 and is stronger and more expensive. The design utilizes a double 2×12 beam with 6×6 posts spaced 6-feet apart, and ledger with joist hangers. The size of the beams and the span between beam support posts, plus the distances between beams and ledger, affect the distance joists must span. If upgrading the size of the lumber for your deck beam means using one less footing, then it might be worth the extra cost as you would save time and effort avoiding digging the third footing. Southern pine with a select or #1 grade is stronger than #2 grade SPF and can carry more weight and span a greater distance. There are Tables that also provide sizing for beams based on span, joist wood type, and grade, as well as beam size, support post spacing, and footing requirements. The more complete the plan, the fewer surprises. Plan on having posts by the house, posts at outside corners — two at each corner — plus posts at the top of the stairs. This information could help you determine which way you’d like to orient your joists. Chapter 5 of the 2018 ICR has a variety of tables that are full of useful information about minimum footing sizes (R507.3.1), deck post heights (R507.4), beam spans (R507.5), floor joist spans based on different dead loads (R502.3.1(1&2)), cantilevers (R502.3.3(1&2) & R507.6), and joist spacing for different decking (R507.7). I'm burying 4x4 posts in Concrete as I did with my large fence. Why? Tables and span calculators frequently provide joist dimensions, span, and spacing values based on a dead load of 10 pounds per square foot (PSF or psf) and a live-load of 40psf. for diagonal placement. The plan needs to identify the number of beams and support posts, the layout and number of joists, and the plan for the deck boards. For example: half a 10-foot span is 5, add 2 is 7. In some jurisdictions, that can take weeks. This is good if you are looking to save a few dollars; however, code will not allow you to space your deck posts as far apart beneath your beam when using 4x4s. If you are unable to attach or don’t want to attach, your deck joists to your house with a ledger board, then your design becomes more flexible. A three-ply 2×12 would allow you to use only two deck support posts for the 10×10 deck. for composite and 5/4 decking, and up to 24”o.c. There is an increase in cost due to more joists but it’s usually marginal in the overall cost. There are several construction methods for installing deck joists. Cedar has a natural wood preservative that protects from rot and insects. Decks get wet and may be framed with incised treated lumber so spans may have to be adjusted. Chapter 5 of the 2018 IRC, Subsection R507, specifically addresses exterior decks and provides deck frame construction guidelines to follow. The most confusing part about understanding how far apart to space your joists is understanding the chart that explains it. Transferring the idea to reality begins with a plan. Tributary Load. JOIST SELECTION CHART Joist Size Maximum joist span between bearers at specified joist spacing 450mm 600mm 90 x 45mm 1.15M 1.00M 140 x 45mm 1.85M 1.60M 190 x 45mm 2.50M 2.15M Eugene has been a DIY enthusiast for most of his life and loves being creative while inspiring creativity in others. Ideal deck post spacing is 8 feet or less. Deck joist spacing is the distance between joists, measured from the center of one joist to the center of the next, and is commonly 12, 16, or 24-inches. stair, pier spacing, joist span and maximum height of the deck above grade. The span is the distance a joist traverses from ledger to beam, or beam to beam, without support. The shape and size of the deck influence the layout and number of joists, potential spans, and even the spacing. The benefit of using 4x4s is that you can put them on a smaller diameter deck footing, which thus requires less concrete and digging. Some equations and algorithms will calculate the span and spacing for joists and numerous joist span tables for reference too. The span tables below indicate exactly how many footings you need with each size of the deck beam. You can opt to use larger lumber, such as three 2x10s, and space your posts nearly 2’ further apart. This is confusing because it is not only telling you the beam span but also telling you maximum distances you can space your deck support posts. Round the span to the nearest foot and add two. It is available in green or brown tones of preservatives, so the color is reasonably consistent. The distance between deck support posts depends on the type of wood species used and the size of the joist and beam. at right angles. Joists distribute the weight of the live and dead loads of the deck to the supports. A shorter beam span means more deck support posts. The spacing depends on the thickness of decking used. Joist Span – Joists Attached at House and to Side of Beam. So using the above examples, a 2-ply 2×8 of SYP can have deck support posts spaced at 8’6” for joists that are only 6’ long. For example, the table will be called something like “deck beam spans”. How the decking runs determines the joist pattern, which in turn identifies the number, size, and placement of beams and support posts, and the ledger board. Lesser Strength: Eastern white pine, ponderosa pine, western red cedar, and SPF have shorter span ratings. The shape and size of the deck are primary considerations, along with its purpose. We’ll also explore how they influence the strength and safety of a deck. They’ll be more than happy to answer your questions and give you a paper copy of your local building code. The more elaborate the deck design, the greater the need for the input of a Structural Engineer. The live load also affects the footing size. My preference is to use span and spacing values readily available in Code tables or calculators. can bridge 18’-6”. Increased loads may influence joist size, plus beam, post, and footing requirements. with a live load rating of 40psf will span 9’-9” while a 2×12 yellow pine at 16”o.c. Maximum cantilever of a 2X8 is 24” at 16” o.c. Joist Span – Non-Ledger Deck. or less if diagonal to prevent sag and bounce. Standard rail … The spacing of your joists indirectly affects how far apart you place your deck support posts. Span and spacing calculators, whether on-line or hand-held, use algorithms to identify the span based on wood type selection, joist size, and spacing. when laid diagonally to joists, and 16”o.c. *Values from Table R507.6 of the 2018 IRC. Tables found in your local building code don’t explicitly say how far apart to place your deck support posts. The last board won’t look good if it’s skinny or cut at an angle. Round up to the nearest whole number, then subtract 1. 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