Building a deck is a rewarding way to increase and improve your outdoor living space. Selecting the best material for the build, however, can be both difficult and expensive. If you’re leaning toward using less expensive lumber, and are wondering, can you use 2×6 for deck joists? We’re here to help!
The size and elevation of the deck along with load expectations determine the framing requirements. For live loads of 40psf, 2×6 joists are ideal if spaced at 12” centers. They can be used for ground-level decks up to 12 feet wide that don’t require railings or stairs.
In this guide, we’ll identify if 2x6s can be used for deck joists, their maximum span, and how much weight they can support. We’ll discuss using 2x6s for ground-level decks, if 2×6 or 2×8 joists are better, and what the best joist size is for a deck. Our aim is to provide you with the information to make the best choice for your deck.
Can You Use 2×6 for Deck Joists?
Using dimensional 2×6 lumber is common for small structures like cabins, sheds, porches, and decks built close to the ground. They are also often used for upper story floors of smaller homes typically used for sleeping. We recommend, though, that plans be checked and approved for compliance with local building codes.
According to Section R507 of the International Residential Building Code (IRC) for 2021, 2×6 lumber can be used for deck joists, deck beams, decking, and railing components. The span distance depends on wood species, grade, spacing between joists, loads, elevation, and other factors. Ledger boards, however, should be a minimum of 2×8 lumber (R507.9.1.1).
No.2 grade pressure treated or naturally resistant lumber is a common choice when building a wooden deck frame. Additionally, all cuts, holes, and notches should be treated with a preservative for greater protection, and waterproof joist tape should be used too.
Ensure all fasteners, hangers, and other metal components are approved for use with the type of wood – some pressure treatments are corrosive to unprotected steel.
How Far Can a 2×6 Deck Joist Span?
The span of a 2×6 deck joist depends greatly on the wood species, grade, spacing, loads, type of deck being built, its elevation, and the location of the beams. A free-standing deck or an attached deck can be cantilevered over the beam or flush with it, which also can affect span.
The general rule of thumb for joists is that they can span 1.5 times their depth in feet. So, a 2×6 is commonly considered to be able to span about 9 feet. However, as with most rules, nothing is that simple.
Floor joist spans differ from the span allowed for deck joists as they have different load and moisture expectations. Based on the 2021 IRC, the span of a typical #2 2×6 deck joist ranges from 5’-9” to 9’-11” depending on all factors, while floor joists can span from 5’7” to 12’-6”.
The Table below identifies the maximum span for a #2 -grade 2×6 based on species, spacing, and load.
|#2-Grade 2×6 Deck Joist Span|
(For dead loads of 10psf)
|* Information from Table R507.6 IRC 2021|
How Much Weight Can a 2×6 Joist Support?
The amount of weight a 2×6 joist can support varies and depends on wood species, grade, load variables, spacing, and span. The load variables include use, type, and duration, and are greatly affected by their application.
It should be noted that while a 2×6 starts out in a rough-cut state true to nominal measurements, it is planed smooth so it is actually 1-1/2” by 5-1/2”. A 2×6 used for a joist is oriented so the narrow face is up or horizontal and the wide face or depth is vertical.
Loads are typically expressed in pounds per square foot (psf) or kilograms per square meter (kg/m²) and identify the amount of weight spread over the tributary area. They are identified as dead load, live load, and environmental loads such as ground snow load, rain, and wind loads. Loads vary with use and geographic location, as well as climate conditions.
The dead load identifies the weight of structural and non-structural materials that are permanent and is usually rated between 10psf and 20psf. Live loads refer to people, furniture, boxes, or moveable and changeable items and commonly range from 5psf to 40psf.
Environmental loads are also a form of live load and can range from 20psf to 90psf. The load a joist can carry is the sum of the dead load and the live load. One key impact to keep in mind is that as the load increases, the allowable span decreases.
To determine the load a deck or floor joist can carry, combine the appropriate live and dead load and multiply the span based on the spacing to get the weight it can support. For example:
- A 2×6 joist used for a living room usually combines a dead load of 10psf with a live load of 40psf for a total load of 50psf. Thus, the joist can support 50 pounds for every foot of the span. So, a select structural (SS) Douglas fir-larch 2×6 can span 11’-4” at 12” centers and support 565 pounds spaced along its span but only 450 pounds if spaced at 24” centers. Under similar conditions, a #2-grade spruce-pine-fir can only support 512 pounds and 404.2 pounds respectively.
- #2 SPF 2×6 deck joists at 12” centers supporting a dead load of 10psf and a live load of 40psf can support 475 pounds along its length and 341.7psf if spaced at 24” centers. However, those supporting ground snow loads of 70psf and similarly spaced will support 633psf and 460psf respectively but along a much shorter span.
Building a Ground-Level Deck With 2×6
A ground-level deck is one built within 30” of grade and may not require railings or stairs. If it is free-standing, a permit typically isn’t required either. A free-standing deck may have joists flush mounted to 2-ply 2×6 beams or resting on 2-ply under-mount beams.
The beams should rest in or on deck blocks, patio stones, buried 6×6 posts, or other solid materials that prevent settling. Consider using 2x8s for the beams for a sturdier deck and extra elevation for improved ventilation.
If the deck is attached to the house, the ledger board must be a 2×8 or greater to meet the code. Plus, the deck construction will require a permit since it is being attached to a permanent structure. Additionally, permanent footings that reach below the frost line are required to prevent settling or shifting which can result in damage to the structure.
To prevent moisture damage and rot, use UC3A (above ground) or UC3B/UC4A (ground contact) pressure treated lumber or another rot-resistant material. It is important also to make sure the deck is well-ventilated. Removing all vegetation from the deck site and some of the topsoil and laying out landscape fabric and spreading gravel will help improve ventilation and decrease moisture issues.
Joist spacing affects the span. Joists at 12” centers span further than those at 16” or 24” centers. The direction of the deck boards also depends on joist spacing too. 5/4” thick decking can run perpendicular to joists at 16” centers or less. Decking laid at a 30° or 45° angle to the joists must be at 12” centers, unless it is 2” thick decking. So, deck board direction affects joist spacing and vice versa.
The joists need to be attached to flush-mount beams using 2×6 joist hangers so they are flush with the top of the beam. A deck with #2 SPF 2×6 joists spaced at 12” centers and flush mount beams can be up to 10’ wide when the beam width is added to both sides.
A drop beam deck using the same type of lumber can be up to 12’ wide when cantilevered on both sides. The joists rest on the drop beams and are usually attached using appropriate fasteners and joist straps.
Some chemicals used in the pressure treating process can corrode steel, so use bituminous joist tape and treated fasteners and hardware to counter corrosion and rot.
Use the joist tape wherever wood meets metal or wood meets wood to improve deck longevity. Remember, all cuts, notches, and holes should also be treated with a wood preservative to protect exposed raw wood.
To be code compliant, decks that are vertically 30” or higher off the ground within 36” of their perimeter require railings or guards. Most codes also state that the rim and band boards along with the joists need to be a minimum of 2×8 to properly support railing posts and stairs. Additionally, decks wider than 7’ require mid-span blocking to prevent joists from twisting under load.
Should I Use 2×6 or 2×8 for Deck Joists?
The size of the deck, load expectations, elevation above grade level, and budget often determine joist size. The choice between freestanding or attached is another common factor that affects choice too. A free-standing deck that won’t require code-compliant railings can easily be built using 2×6 joists.
A 2×6 is lighter and less expensive than a 2×8 of similar grade, species, and treatment. Ground contact pressure treated 10’ 2x6s are up to 30% less expensive and 12’ lengths between 15% and 20% cheaper than equivalent 2x8s. Using 2x6s will save about $80 on a 10’x10’ deck with joists spaced at 12” centers and a live load of 40psf but only about $45 on a similar 12’x12’ deck.
Use 2×6 pressure treated lumber if the live load is 40psf and you’re building a 10’ or 12’ wide free-standing deck that doesn’t require railings. 2x8s are stronger, more rigid, can span further, and support greater loads as well as provide compliance for railings and stairs if required. So, use 2x8s for attached decks or those that require railings, or need to support loads greater than 40psf.
What Is the Best Joist Size for a Deck?
Joist size typically depends on numerous factors that optimize potential building materials and budgetary constraints. Using 2×12 joists at 12” centers for a deck that only requires 2×6 joists at 12” centers is a waste of money and resources.
The best joist size for a deck is determined by its elevation, size, span, load variables, decking plan, and any building code requirements. Use 2×6 joists at 12” centers for ground-level decks less than 30” off the ground and up to 12’ in width with live loads of 40psf.
For decks that require railings, stairs, longer spans, or need to support heavier loads, use joists of greater depth or add an extra support beam. Hopefully, you now have the information to make the best choice for your deck.