Building a deck is much like building a house. It requires a foundation, floor, walls, and sometimes even a roof. The parts of a deck mesh together to form a strong outdoor living platform. Understanding the terminology makes planning and building easier and more enjoyable, and the finished deck safe for entertaining and relaxing.
In this guide, we’ll take a look at the anatomy of a deck and explain the terminology. We’ll discuss the different deck components and their purposes. This guide will provide you with a better understanding of deck construction and what different terms mean. Hopefully, by the end of the guide, you’ll be better prepared to build a deck or have one built.
- Parts of a Deck
- Deck Frame
- Ledger Board
- Concrete Footings/Piers
- Concrete Blocks
- Support Post/Column
- Post Connectors/Anchors
- Beam-Post Connector
- Deck Rim Joist
- End Joist
- Joist Hanger
- Joist to Beam Connector
- Deck Boards/Decking
- Hidden Fasteners
- Top Rail/Cap Rail/Handrail
- Bottom Rail/Base Rail
- Rail Post/Newel
- Total Rise
- For example:
- Total Run
- Stairs Landing
- Drainage System
Parts of a Deck
When starting out it is always best to begin at the bottom and work upward. Instead of an alphabetical list of deck part names, our list starts where your build begins and follows the common progression of deck terms from start to finish. The IRC notes in Section R507.2.1 that wood used for deck construction must be #2 grade at minimum. It should be naturally durable and resistant to insects and rot (R318) or treated with preservatives (R317). All cuts, drill holes, and notches should also be treated with preservatives (R317.1.1).
Note: For deck construction Building Code requirements, we reference parts of Chapter 3 and much of Chapter 5, Section R507 and its subsections in the 2018 International Building Code (IRC). The IRC guides, in whole or in part, the national and local codes in the United States and Canada. The IRC sets the minimum building requirements for safety, so there may be local differences. It is best to check local codes or with a Structural Engineer or the local Building Inspector.
The deck frame is all the structural components that support the decking and is based on the deck frame plan. The plan identifies all parts of the frame, including dimensions and connecting hardware. The ledger, footings, support posts, beam(s), hangers, joists, and rim boards are all parts of the deck frame.
The ledger board is commonly fastened to or through the wall of a building or its rim joist with approved bolts or structural screws with code determined spacing (Tables R507.9.1.3(1) & (2)). It is one or more horizontal pressure treated #2 or better 2×8 – or larger depending on joist dimensions (R507.9.1.1) butted together. The ledger determines the deck’s width, and joists are attached perpendicular to it with hangers.
Flashing or ledger cap flashing is waterproof and corrosion-resistant metal or vinyl that prevents moisture seepage into the building (R507.2.4). It protects the wall and ledger board. Flashing may be galvanized or stainless steel, vinyl, or copper and is available in pre-formed lengths or rolls that can be shaped.
Footings of concrete or other approved material or systems support the loads the structure will carry (Table R301.2(1)). The size of the footing is based on the loads it will carry (R507.3) and the footing depth (R403.1.4.1) based on soil and frost conditions. The footings are the structural foundation of the deck. The placement and number of footings are based on the deck frame dimensions, beam size, and joist size and span. Here are two of the more common footings used for decks:
Concrete footings and piers are often used for decks that are 30” or more above ground level. Concrete footings may be formed and poured below frost level or at grade level. They support posts that sit directly on, in, or fasten to an anchor set into the concrete. A concrete pier is usually cylindrical in shape and starts below the frost line and projects above grade level. It commonly has an anchor embedded into the top for the support post, but the post may also be sunk into the concrete.
Concrete blocks or deck blocks often sit on a bed of gravel and are used for ground or low-level deck structures – within 30” of the ground. They often support lighter loads than piers or footings.
Support posts or columns are vertical supports for the deck beam that transfer the deck loads to the footings. They are frequently wood or metal, but may also be concrete. The dimensions of the posts depend upon the height the deck is off the ground (Table R507.4) and the loads they must support.
Beams are the parts of a deck structure that carry and support the joists. Depending on span and wood species (Table R507.1), it is commonly one to four pieces of dimensional lumber thick. It may also be solid timber or steel. The beam planks must be minimally attached together with 10d nails every 16-inches (Section R507.5). Beams may cantilever support posts by up to 1/4 the allowable span between support posts.
Support posts that sit on concrete footings or piers must have lateral support provided by a manufactured metal bracket or connector embedded in the concrete (R507.4.1). Alternatively, the post must be embedded a minimum of 12” into the concrete pier. The connector is corrosion-resistant and usually elevates the post off the concrete to prevent moisture damage and rot. Simpson Strong-Tie brackets, concrete screws, and Post Base Bracket Kits are some options available.
Support post to beam connections must resist lateral displacement while transferring vertical loads (R507.5.2). Beams may be fastened to notched posts that fully support the beam and fastened with carriage bolts (Figures R507.5.1(1) & (2)). Beams may also be attached to posts using appropriately sized post-beam connectors manufactured for the purpose. Fasteners must also comply with code requirements.
Deck joists are usually dimensional lumber that makes up the deck structure. The joists carry the decking and span from the ledger to, or over, the deck beam, or to, or across, two or more beams. The maximum spans (Table R507.6) depend on wood species and spacing between joists and the type of decking material (Table R507.7) to be used. Joists range from 2×6 to 2×12 and are commonly spaced 12” or 16” on center, but can be up to 24” apart. The cost of 2x6s vs 2x8s or 2x10s is often the determining factor on which is used for deck joists, as is the distance it must span, which makes 2x6s the frequent choice.
Deck Rim Joist
An important structural part of the deck framework is the rim joist. It attaches perpendicular to the joists and across the open joist ends, closing the openings, and helps maintain spacing between joists while preventing joist rotation or twisting (R507.6.2). Often of material similar in dimensions to the joists, it also provides support for attaching stairs and railing posts.
The outermost parallel joist at each side of the deck is often called the end joist. They are also frequently referred to as rim or band joists, or faceplates. The end joists shape the deck, support decking, and structurally make for a more rigid and cohesive framework. Decking, stairs, and railing posts often fasten to the end joists,
Blocking is pieces of joist material installed between and perpendicular to the joists. They bridge or join joists, unifying the framework, and decreasing lateral movement, sway, bounce, and preventing joist rotation. Many deck builders install blocking or noggins in a straight-line, herringbone, or zig-zag pattern every 4’ to 6’. However, the code only requires blocking to close the opening at joist ends or every 8’ on joists greater than 2×12 (R502.7). Additional blocking is often used between end joists and rim joist to provide extra backing and support for railing posts.
Joist hangers are commonly used to support and attach joists to the ledger board, beams, and to connect other deck members where a direct nailing connection is difficult. Hangers are manufactured from galvanized or stainless-steel and require structural fasteners. Joist hangers are available in different configurations and angles to support multiple joists and different deck construction angles.
Joist to Beam Connector
Joists that bear on a beam are often attached to the beam using a galvanized or stainless-steel joist to beam connector. Hurricane ties such as those from Simpson Strong-Tie secure joists to beam and prevent lifting or lateral movement or twisting. Joist hangers may also be used to fasten joists to the face of a beam.
A cantilever is an overhang by a structural member. A beam may extend past or cantilever a support post by 1/4 of the allowable span between support posts (R507.5). The distance joists may cantilever a beam is determined by the wood species, dimension, spacing, load, and span between the ledger and beam or beam to beam. The rule-of-thumb is 1/4 of the span, however, Table R507.6 identifies the allowable cantilever by species, spacing, and span, so it’s best to go with whichever distance is less.
Braces are diagonal structural 2-by or 4-by pieces that provide lateral support to a deck structure. They improve the integrity of the deck and prevent sway as occupants move around. The ends of the braces are often cut at 30° or 45° to fit between the support posts and the beam, or post and joist on freestanding decks. Braces are fastened to post and beam or joist with approved structural screws.
Deck boards commonly are 5/4”x6” or dimensional 2-by material with a 1/8” to 1/4” gap between boards. They may have a natural insect and decay resistance like cedar, redwood, Ipe, teak, or mahogany. Alternatively, decking can be chemically pressure-treated to resist insects and rot. Some other options include composite decking, PVC or plastic planks, or aluminum boards.
Deck boards commonly are laid perpendicular to the joists, but may be installed diagonally to the joists or in parquet, basketweave, chevron, or herringbone patterns, or customized. Plywood or other untreated lumber may also be used for covered or protected decks. Check for specific code requirements in Section R507.2 and its subsections.
Hidden fasteners are metal, plastic, or fiberglass clips with wings or flanges that go into grooves or slots manufactured or cut into the sides of deck boards and fasten to the joists. The fasteners secure the decking and maintain a uniform gap between boards. Some hidden fasteners are screw and plug and install into the top of the plank instead of the side. The plug makes for an almost invisible connection between a joist and a board.
The railing is a system of posts and rails designed to guard against trips, falls, and injury (R312.1). Decks 30” off the ground in much of the USA must have a railing 36” above the deck surface, while in Canada decks between 23-5/8” and 71” must have a 36” railing, and 42” on higher decks. Currently, railings must withstand a 200-pound push or pull force against the top, but there is much discussion about raising that to 500-pounds. Some states or jurisdictions may have different requirements, so it’s best to check.
Although railings have a safety function, they often accentuate personal or architectural flair. Railings are frequently made of wood, metal, glass, vinyl, or composite materials, and some even use stainless steel cable or rope. Railings are often a blend of different materials and compositions.
A balustrade is another term for a railing, guard, or banister. It includes the vertical and horizontal components that form a barrier or wall, and help to prevent falls. It is often used to identify ornately turned or formed guards on porches, decks, terraces, stairs, bridges, and even the eaves of some buildings.
Top Rail/Cap Rail/Handrail
The top or cap rail refers to the uppermost horizontal railing member that tops or caps vertical spindles or balusters. It may be made of wood, metal, plastic, or other approved materials. On many decks, it is a 2×4 or larger dimensional piece that runs between or atop railing posts. The top or cap rail may differ from a handrail in height, width, and depth. While the top or cap rail must be either 36” or 42” above the deck and can vary in width and thickness, a handrail must be between 34” and 38” (R3220.127.116.11) above the walking surface and of graspable diameter (R318.104.22.168).
Bottom Rail/Base Rail
The base or bottom rail is frequently a 2×4 run parallel to the top rail. It often supports and maintains the spacing of spindles that vertically span between the top and bottom rails, but may also be used to hold or stabilize other barrier materials like wire mesh or glass panels. The distance between the bottom rail and the deck surface can’t allow passage of a 4” sphere, so it must be smaller than 4”.
Although many use baluster and spindle interchangeably, they aren’t the same. Spindles are turned or square vertical parts of a railing and span between the top or handrail and the bottom rail. They form a raised barrier or guard of wooden or metal pickets. Balusters are vase or jug-shaped pieces mounted directly to or set on a terrace, deck, floor, or bridge. They do not have a bottom rail and are often made of stone, concrete, iron, wood, or plaster.
Railing posts or newel posts are attached to the deck structure. They anchor and support the railing components and must withstand lateral forces applied in any direction against the railing. The posts may be the same height as the top rail or extend above it.
Railing posts are often 4×4 or 6×6 timbers that bolt to the rim or end joists and blocking. Notching 6×6 posts to fasten to joists is acceptable in many areas, however, notching 4x4s isn’t. Posts should be fastened to the deck structure in such a way that forces are shared between multiple components of the deck framework.
Stairs are used to traverse changes in elevation. Stairs should be a minimum of 36” wide (R311.7.1) and able to withstand a live load of 40psf uniformly, or a concentrated load of 300-pounds over 4 square inches (Table R301.5). Deck stairs are made up of stringers and treads, and sometimes riser boards. Those with riser boards are called closed and those without, are called open. Stairs commonly have a 7-inch rise for every 10-inches of run and should be securely fastened to the rim joist using appropriate fasteners and/or connectors.
Stringers, strings, or stringer boards are sloped 2x10s or 2x12s (or other acceptable material) that connect the deck with the ground or to different structure levels. They are the structural components that carry the steps upon which people tread. There are two styles of stringers. Open or saw-toothed are also known as Eastern stringers. Closed, boxed, housed, or solid are uncut stringers and known as Western stringers. Stringers can’t exceed 151” in vertical height (R311.7.3). Stringers may be secured to the deck prior to attaching the treads, or after the stairs are assembled.
Treads or steps are the surfaces upon which the foot is placed as one ascends or descends the stairs. The tread is commonly rectangular and clearance must be 10” or more in depth from the leading edge of one tread to the next at the walkline (R322.214.171.124.1). Treads may be made of wood, metal, concrete, or other approved material.
The riser is the vertical or sloped component that closes the vertical gap between treads on closed stairs. The riser, from the top of one horizontal tread surface to the next, shouldn’t exceed 7-3/4” in height (R3126.96.36.199). Additionally, open risers (stairs without risers) that are 30” or more above the ground or floor can’t allow a 4” diameter sphere to pass through. Risers are often made of wood, metal, glass, or other materials.
The total rise is the vertical distance between the ground and the deck surface, or different deck or floor surfaces. Remember, the rise cannot exceed 151” without a landing. The rise helps determine the run or number of treads. Measure the distance from the horizontal deck surface to the ground or next level. Divide the distance by 7” – the most common distance between horizontal step surfaces – to identify the number of steps. The maximum rise between treads may be 7-3/4” and the greatest deviation between all can’t be more than 3/8” (R3188.8.131.52). To achieve an even number of treads, it may be necessary to adjust the value the total rise is divided by.
- Total rise is 50-inches
- 50” ÷ 7” = 7 steps with 3” left over
- 50” ÷ 7-1/8” (7.125”) = 7 steps
Note: A uniform rise is desirable.
- The total run for 10” deep tread
- 7 steps x 10” = 70”
The total run is the horizontal distance from the face of the deck to where the stringers will rest upon the ground. It is commonly calculated by multiplying the number of treads by 10” which is the minimum allowable tread depth (R3184.108.40.206) – see the example above.
There should be a floor or landing at each end of a stair flight. The landing should be the same width and depth as the width of the staircase (R311.7.6). Thus, a 36” wide stairway would require a 36”x36” landing area.
To prevent weed growth and moisture settling under a deck it is customary to roll out landscaping cloth and cover it with 6” of washed gravel. The gavel allows moisture to percolate into the ground while providing a dry level surface on which to store outdoor items. The ground cloth prevents weeds from sprouting or taking root easily.
In addition to, or as an alternative, there are other systems that can be installed above, between, or under joists to catch run-off and redirect it to a common drain or collection point. The drainage systems are of PVC, vinyl, EPDM, HDPE, metal, or other materials. Some protect the joists from moisture damage and need to be installed prior to the deck boards, others do not. Cost and ease of installation may be determining factors in their purchase.
Building a deck is a great way to extend your living and entertainment area outdoors. Understanding deck terminology will prove beneficial when building or hiring a pro. It’s always good to ‘know’ what deck part names mean when talking to inspectors, builders, or suppliers, so you’re all on the same page. Hopefully, you have a better understanding of deck terms and the parts of a deck.