Deck Building Code Requirements

Building a deck is a great way to add value to a home and create an outdoor living space. Unfortunately, many decks don’t comply with deck building code requirements and daily put guests and family members at risk. Improperly built decks have failed in the past, causing injury and death, and damage to property. If you’re planning to build a deck or have one built, understanding the code requirements is a great way to start.

Building codes focus on safety and set guidelines for construction to ensure builds are safe for occupants. The codes are constantly being updated based on building and material improvements, and experience learned around the globe. Adherence to the building code means your deck meets the minimum construction and safety requirements for footings, posts, beams, joists, decking, railings or guards, and stairs.

In this guide, we’ll discuss the building code for residential decks and look at the 2021 International Residential Building Code (IRC) requirements for different deck components. We’ll also explain freestanding deck codes, the Florida deck building codes, and where to find the code for existing decks. Our goal is to provide you with an understanding of the code requirements for your decking project.

Deck Building Code Requirements

What Is the Building Code for Residential Decks?

Building codes have been around for thousands of years, but the first building code in the USA came into being in New Amsterdam, modern-day New York, in 1625 and addressed fire safety and roofing materials. Codes or ordinances were localized to individual communities and often varied from place to place, while outside settled areas, they were nonexistent. Most were a knee-jerk reaction to something, that in retrospect, seems obvious – wood chimneys and thatched roofs weren’t considered safe in town limits where sparks could set the whole village or town aflame.

Modern building codes continue to address health and safety issues and are based on centuries of research, best practices, and failures. However, it wasn’t until the mid-1990s with the formation of the International Code Council (ICC) and the merging of three major US regional building codes that a national U.S. building code model came into being. In 2000, the first International Building Code (IBC) and International Residential Building Code (IRC) were published.

Canada published its first National Building Code (NBC) in 1941, and over the subsequent decades, it has become the foundation of its provincial, territorial, and municipal building codes. It is now updated and published on a five-year cycle, with the most current NBC being the 2020 edition.

Like the IRC, the NBC sets the minimum requirements, and similarly, each Province and subsequent municipality adapt it to their conditions – often being one or two cycles behind the current national code. There are similarities between the IRC and the NBC, however, there are also differences, so always check with the local building department to be code compliant.

The IRC addresses one- and two-family dwellings while the IBC applies to all other structures. The codes continue to address minimum building requirements for fire and safety issues but from a construction and design perspective. The size, number, and location of structural members, fasteners, and exits are covered, as is everything from footings to roofing finishes. There are also structural requirements for earthquakes, hurricanes, tornados, wind loads, and snow loads which apply to different regions.

Every three years the ICC updates the IBC and IRC based on new building materials, practices, and intensive testing of building materials by different independent agencies and individuals, including the American Wood Council (AWC) and NADRA (North American Deck & Railing Association).

Changes to the 2018 Codes were based on 309 proposals that lead to many of the updates in the 2021 Codes. The IRC and IBC are living documents that utilize lessons from the past and present for future building practices. In 2012, the section of the IRC that addressed outdoor decks – R507 – was only 2-1/2 pages long, in 2015 it was 6-1/2 pages, 11 pages in 2018, and even longer in 2021 IRC.

Much of the US, with the exception of Wisconsin, uses some version of the IRC as the foundation of their State and local building codes. So, if you’re building a deck or having one built, Section R507 of the 2021 IRC is the one to check, although your local Building Inspector will reference the local code which may differ in some respects. However, building to the most current IRC will mean greater safety and structural compliance, and provide more protection to family and friends.

Deck Building Code Requirements

Deck building codes

In the U.S., Section R507 of the IRC is the foundation of most building departments’ residential deck building code requirements. It should be noted that IRC 2021 contains numerous additions or changes to Section R507 over previous editions. Additionally, many municipalities are one to three cycles behind the most current published edition, so always check locally to be code compliant.

The information in the sections below is drawn from the 2021 edition of the IRC and is presented to assist in the design and construction of a code-compliant deck. The identified tables and drawings in the sections are fairly easy to follow, and electronic access is free. However, all designs more than 100sqft and more than 24-inches off the ground should be checked by a Structural Engineer or the local building department.

All fasteners and connectors should meet the requirements set out in Table R507.2.3. Nails, bolts, lag screws, nuts, washers, and glulam rivets must be hot dipped galvanized, stainless steel, copper, or silicone bronze. While metal connectors are to be zinc-coated galvanized, hot dipped galvanized, or stainless steel.

Additionally, any decks within 300’ of saltwater shoreline must use only stainless steel fasteners and connectors. Flashing used must be at least 0.019” thick corrosion-resistant metal according to R507.2.4 or other approved material compatible with the deck framing and decking materials.

Ledger Board

Section R507.9.1.1 states ledger boards must minimally be 2×8 pressure-treated Southern pine or incised pressure-treated fir or other acceptable No. 2 grade or better lumber. The ledger must be equal or greater in depth to the depth of the joists, so if using 2×10 joists, the ledger must be 2×10 or greater.

The ledger should be fastened to the building’s band joist, not to masonry, brick, or stone veneer, nor should it support beams or girders. Flashing (R507.2.4) also needs to be of a minimum thickness and compatible with deck material and the structure’s substrate.

Section R507.9.1.3, plus Table R507.9.1.3(1&2) and Figure R507.9.3(1&2) address fastener spacing, placement, and size. Connect the ledger to the band joist using 1/2″ diameter galvanized or stainless-steel lag screws. The spacing is based on load, joist span, and the thickness of structural sheathing over the band joist.

Section R507.9.2(1&2) addresses lateral connections using hold-down tension devices to transfer lateral loads to the ground. A minimum of two devices with a load capacity of 1500 pounds or a minimum of four 750-pound load capacity devices must be used. They should be placed no closer to the ends of the deck than two feet are required. The type and location depend on whether the interior floor joists are parallel or perpendicular to the deck joists.

Footings

 

Deck Footing Requirements

Section R507.3 addresses footings and states decks are to be supported by concrete footings. Other approved structural devices or systems designed to support loads identified in Section R301 may be used instead of concrete. Figure R507.3 identifies acceptable footing to deck post connections. Stainless steel or galvanized post anchors set into the concrete to receive 4×4, 6×6, or larger posts are recommended, but individual products are not specified.

Table R507.3.1 identifies the minimum footing size based on soil load-bearing values, live or snow loads, and deck tributary area. The greater the tributary area and load, the greater the footing requirement. Additionally, the weaker the soil strength, the larger and thicker the footing required.

A tributary area of 80 ft² with soil strength of 1500psf requires a square footing with 20” sides or a round footing 19” in diameter with a thickness of 7” at a live load of 40psf. Increasing the live or snow load increases the footing size, while stronger soil strength can decrease footing dimensions.

Section R507.3.2 identifies the minimum depth as 12” below undisturbed ground level. However, where frost may be present, Section R507.3.3 directs that the footings extend 6” below frost level and rest on undisturbed soil as specified in Table R301.2, or set on solid rock, or other approved options. However, in some cold winter regions, 12” to 24” below frost level may be locally recommended.

The tributary area is often used to identify the spacing between footings. But the spacing is also affected by beam depth, joist span, number of angles, and additional factors like supporting a roof or hot tub. Table R507.5(1,2,3&4) identifies deck beam span, which translates into footing spacing, based on beam size, wood species, live or snow load, and the effective joist span.

Posts

Deck post spacing

Section R507.4 and Table R507.4 provide information on the maximum deck post height for single-level decks measured from the top of the footing to the underside of the supported beam. Posts are to be #2 grade or better, incised or not, and rot resistant or pressure-treated if in contact with the ground or near the ground. The height of the deck post is based on post dimensions, live or snow load, wood species, and tributary area. For single-level decks, the maximum height identified in Table R507.4 is 14 feet. So, if you need to go higher, consult a Structural Engineer.

Most contractors use pressure-treated lumber for all the deck frameworks as it tends to be less expensive than cedar, redwood, or other exotic woods, metal, or synthetic materials. Although the Code allows for 14-foot 4x4s to support the tributary area of a single-level deck, the practice is to limit 4×4 use to 10 feet and use 6x6s if going higher. Another common practice by many builders is to use only 6×6 posts as they are easier to secure to beams and support greater loads.

Posts sitting on concrete footings or precast footings need to be fastened to the footings to prevent lateral or uplift movement. Check Section R403 and Figure R507.3 for more post-to-footing connection information. However, posts set 12” or more into the ground or into concrete do not require fasteners.

Additionally, diagonal and lateral bracing may be required for stability, or due to wind or seismic issues. Diagonal bracing should minimally be dimensional 2x4s fastened with 1/2” through bolts that meet the criteria set out in Table R507.2.3, and vertical and lateral supports (R507.8) must meet those outlined in Table R301.5.

Beams

Deck Beam

Section R507.5 identifies the maximum spans of wooden deck beams and that beams may be cantilevered at the ends by up to 1/4 of the actual unsupported span. Beams fabricated of 2x plies must be fastened together using 10d (3”x0.128”) nails or greater. The nails should be in two rows, with each row no further than 1-1/2” from either edge and spaced at 16” centers.

Beams may be dropped so joists sit upon them or flush so the joists fastened between them, as shown in Figure R507.5. Table R507.5(1,2,3&4) identifies the maximum deck span based on live or snow load, species, beam size, and effective joist span. The thicker the beam, the greater its span in relation to the other factors.

Section R507.5.1 and Figure R507.5.1(1&2) address deck beam to post bearing, splicing, and connection. Splicing must occur at a post and at least 1-1/2” of the full width of the beam must be supported on wooden or metal posts, and 3” on concrete or masonry posts. Beams are to be fastened to wooden posts using 1/2″ dia. stainless or galvanized through bolts with washers at each end or equivalent approved connectors.

Beam-to-post connections may be on top of the post with an approved cap or notched into the post following the guidelines outlined in this section. Section R507.5.2 relates to ensuring the proper transfer of vertical loads and resisting horizontal movement.

Joists

Joists

Deck joists typically span from ledger to beam or beam to beam, and are fastened using joist hangers, mechanical fasteners, post caps, or notched into posts. Joists may cantilever up to 1/4 of their span, and the maximum allowable overall span is identified in Table R507.6. Span is based on load, wood species, joist size, and the spacing between joists.

Standard joist spacing for wood decking, according to Table 507.7, is 8”, 12”, 16”, and 24” on center (OC) and is typically determined by the type, thickness, and orientation of the decking. Spacing for plastic composite deck boards, according to R507.2.2.1, is identified on the manufacturer’s labeling, but typically is the same as for wood decking of the same nominal thickness.

Section R507.6.1 addresses deck joist bearing. Joists must be supported by at least 1-1/2” on wood, with a metal hanger or bracket, or at least 3” on concrete or masonry over their full width. Joists resting on top of a multi-ply beam or ledger are to be fastened as outlined in Table R602.3(1), while joists bearing atop single-ply beams or ledger are to be secured using approved mechanical fasteners. Joists that attach to the face or side of the ledger or beam are to be secured using approved joist hangers.

The open ends of the joists also require a rim joist according to R507.6.2 as a lateral restraint to prevent rotation under load. The rim joist must be fastened with three 10d (3”x0.128”) nails or 3” #10 wood screws. Where joists are supported by joist hangers, blocking is required at half span or every 8 feet. Blocking depth should be at least 60% of that of the joist. R507.9.1.2 addresses solid band joists thickness and R502.1.7 identifies engineered lumber rim board thickness.

Decking Boards

Deck Board Spacing

Deck boards may be untreated wood, treated wood, plastic, plastic composite, or other approved materials. Decking, according to R507.7, should be fastened to each joist with at least two approved #8 wood screws or two 8d threaded nails, or other approved fasteners in adherence to the manufacturer’s directions. Many plastic composite decking manufacturers also manufacture proprietary fastening systems or recommend one for use with their products.

The orientation of the deck board to the joists determines the spacing between joists, so deciding to change the decking orientation after the joists are in place, means either moving the joists or using thicker deck boards. Table R507.7 identifies the maximum joist spacing based on decking thickness, orientation, and single or multiple spans. Single span means the deck board is supported by only two joists, and multiple spans refer to support by three or more joists.

IRC 2021 identifies the maximum angle from perpendicular as 45°, so decking could be oriented at 90° or 45°, or another angle less than 45°. At 90° or perpendicular to the joists, 5/4 decking has a multiple span of joists spaced at 16” OC, and 2” decking 24” OC. Angling at 45° to the joists, 5/4 drops to 12” OC and 2” to 16” OC. If using plastic composite decking, check the manufacturer’s labeling for joist spacing for their product.

Although not identified in the IRC presently, 5/4” decking laid at 60° changes joist spacing to 14” OC and 8” for 30°. The joist spacing for 2” decking at those angles requires joist spacing of 22” OC and 12” OC respectively. Always check with a Structural Engineer or local building department when deviating from the Building Code.

Spacing between wood decking typically ranges from 1/8” to 1/4″ to allow for swelling and twisting. However, wider gaps of 3/8” are common to allow water to drain more quickly. For plastic composite decking the side-to-side gap is commonly 3/16” and the end-to-end gap 1/8” if the temperature at installation is greater than 40°F.

Deck Railing

 

Standard Deck Railing Height

Deck railings or exterior guards are addressed in Section R507.10 of the IRC and specify how the railing posts need to be secured to prevent failure and joist rotation. The section further identifies that railings must also meet Sections R301.5 regarding live load distribution against guards and R312 requirements for railing location, height, and opening limitations.

According to R312.1.1, decks 30” or more off the ground, or those on sloped ground where the horizontal elevation within 36” of the deck is 30” or more, require a code-compliant guard rail. The height of the railing according to R312.1.2 is at least 36” high, and openings between or below balusters won’t allow a 4” diameter ball through. Railings, according to Table R301.5, must also be able to withstand a concentrated load of 200lbs applied in an outward direction against the top of the guard.

Posts attached to the sides of joists require two 1/2″ bolts and hold-down anchors rated for 1800 pounds to transfer the load to other joists and prevent joist rotation. Fastening supports to end grain is not permitted. If using 4×4 wooden posts, they can’t be notched for connection to joist or beam.

Guards fastened to the deck surface must be connected to the deck framework or blocking connected to the framework, per the manufacturer’s instructions. Plastic composite guards and those of other materials must be installed in accordance with the manufacturers or Engineer’s directions and comply with R507.2.2.

Deck Stairs

Deck stair code

Deck stairs shall be manufactured from treated lumber or other approved material and comply with Section R311.7. Treads will be a minimum of 31-1/2” wide at and below the handrails according to R311.7.6. The rise being not more than 7-3/4” (R311.7.5.1) and the tread depth not less than 10” (R311.7.5.2). The railing will be vertically between 34” and 38” above the stair nosing or sloped plane, in accordance to R311.7.8.1. Landings and stairs treads may also have a 2% slope for drainage (R311.7.7).

Stairs must be anchored to resist lateral and vertical forces or be free-standing and meet all Code requirements. Stringers may be made from pressure-treated 2x12s, metal, engineered wood, or other approved material. If notching for the tread, the throat or uncut perpendicular distance from the bottom of the stringer to the inside corner of the notch shall be at least 5”, so the stringer needs to be a 2×12 or larger.

Stairs that rise 12’-7” or higher must have a landing of 36” in the direction of travel and the same width as the stairs. The landing should be constructed to comply with codes for a free-standing deck. Spiral and other stairways are addressed in subsections of R311.7.10 and must comply with those requirements, so always check with your local code or a Structural Engineer.

Freestanding Deck Code

Freestanding Deck Code

There are several reasons a freestanding deck may be preferable to a ledger deck, such as masonry or brick veneer, flashing concerns, local codes, taxes, permits, or easement issues. It is best to check with the local building department before beginning any deck structure.

A freestanding deck is a self-supporting deck and isn’t attached to or supported by any other structure, although it may abut one so as to be almost attached. Most building code requirements for a ledger deck apply to a freestanding deck, however, there are a few exceptions.

Section R507.3 identifies under ‘Exceptions’ that freestanding decks with joists supported their entire length at grade do not require a footing. Footings are also unnecessary if the joists are supported at grade by precast concrete pier blocks without the use of posts or beams, the area doesn’t exceed 200ft², and the deck surface is vertically 20” or less above grade within 36” of the deck’s exterior perimeter. If the freestanding deck doesn’t meet those criteria, it will require footings that meet Table R507.3.1 requirements.

Figure R507.6 identifies dropped beam and flush beam construction for freestanding decks with post and beam construction on appropriate footings. Even with footings reaching 8” below the frost line, the deck is still classed as freestanding, it just won’t flex and adjust with seasonal ground movements like one on precast pier blocks.

It should be noted too, that lateral and diagonal bracing is important with freestanding decks constructed with posts and beams and more than 24” above grade as there isn’t a structure to anchor the deck to or with. Plus, freestanding decks need to be anchored to the footings to prevent uplift and racking.

Florida Deck Building Codes

The current Florida Building Code for deck building is R507 of the 2020 7th Residential Edition. It is similar to the IRC with several modifications due to the frequency of hurricanes, proximity to salt water and airborne salt moisture, and the abundance of moist ground and termites. Section R507 addresses exterior decks, with R507.1 identifying that wood-framed decks must comply with this Section and those of other materials with R301. Additionally, fasteners used in the framework must be stainless steel or hot dipped galvanized to resist corrosion.

Any deck materials containing wood, cellulose, or other biodegradable content must be decay resistant (R507.2.3) and termite resistant (R507.2.4) and comply with ASTM D7032. Footings (R507.3) must be sized appropriately to the imposed loads, at least 12” below the finished grade, and meet R403.1.4 requirements. Deck posts (R507.4) for single-level decks are limited to 8’ using 4x4s or 4x6s, and 14’ using 6x6s. Post to footing connections (R507.4.1) must prevent lateral displacement and wind force lift.

The maximum deck beam span for specified joist spans is identified in Table R507.5, and single-ply beams are not permitted unless they are 4×6 or larger. Post-to-beam connections (R507.5.1) must be attached in accordance with Figure R507.5.1 unless bearing directly on the footings. Deck joist spans (R507.6) are identified in Table R507.6, and joist spacing is determined by the decking material. Joists must be properly fastened to beams in accordance with R507.6.1.

R507.8 addresses vertical and lateral supports or attachments and is much more in-depth in the 2020 Florida Code than the 2018 IRC. However, much of what the Florida code adds is contained in R507.9 and R507.10 of the 2021 IRC. If in doubt, consult a Structural Engineer or the local building department.

How Do I Find the Code for My Deck?

There are several ways to find the code for a deck. If in the planning stage, an internet search of your local municipal government’s building department should provide links to access current deck building codes. You may have to go to your state’s website and follow the links to find those that apply to your local area. Alternatively, give your local government office a call or drop in and ask – they may even provide a paper copy for free or at a minimal charge.

You can access the 2021 IRC online and design your deck to the most current code model, and submit it for permit approval to your local building department. It should be noted, though, that many local codes are one or more update cycles behind the most current IRC. However, as long as the design or build meets their minimum standards, approval is commonly given.

If you’re looking at an existing deck, its age will often determine what vintage code it was built to, if any. The type of fasteners or hardware may also hint at the age, as may lumber stamps or tags.

If you can determine the approximate age, an archival search at your local municipal office should provide the code requirements to which it was built. I have dealt with several local areas though, that are termed ‘unorganized’ municipalities, which typically meant they didn’t have a building department. So, many structures aren’t necessarily built to any specific code.

Older decks are commonly grandfathered so they don’t need constant upgrades. However, if there are glaring oversights where safety is concerned, you may want to make alterations or the local inspector may order them to be made. Railings are especially a concern as they can be a hazard to small children falling through or getting stuck, or if someone leans on it and it collapses, or if they don’t exist at all.

Conclusion

Deck building code requirements are in place to ensure decks are safe for use and won’t fail and cause injury, death, or structural damage. Section R507 of the 2021 IRC addresses footings, posts, beams, joists, fasteners, decking, guards or railings, and stairs. Some local governments publish their own based on State or national codes such as the IRC.

It is always best to check local ordinances before designing and building a deck or using the most recent edition of the IRC. Hopefully, you have a better awareness of the building code as it applies to decks and are ready for your next deck-building project.

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