A 2×6 is a versatile piece of dimensional lumber suitable for a diverse range of structural needs, ranging from beams for decking to rafters for a roof. While a 2×6 can handle a broad range of applications, determining how far a 2×6 can span when used for structural framing can be difficult to calculate.
A wide range of variables determine 2×6 span requirements, ranging from weight load, spacing, wood quality, and wood species. This can make answering the question, how far can a 2×6 span without support? A challenge, to say the least.
A 2×6 spaced 16 inches apart can span a maximum distance of 13 feet 5 inches when used as a rafter, 10 feet 9 inches when used as a joist, and 6 feet 11 inches when used as a deck beam to support joists with a 6-foot span.
In this article, we’ll delve deeper into the distances a standard 2×6 can span, whether you’re using this common dimensional lumber as decking for a backyard deck or rafters in a roof.
- What Is Span in Construction?
- What Factors Impact How Far a 2×6 Can Span?
- How Much Weight Can a 2×6 Support Horizontally?
- How Far Can a 2×6 Span Without Support
What Is Span in Construction?
The term span comes up a lot whether constructing a home, shed, or deck. Span refers to the distance a piece of dimensional lumber can cover before it needs to be supported by a foundation or support post.
When span guidelines are given, they refer to the distance between the center of one support to the center of another. So, in the case of deck beams, span refers to the distance between the center of one support post to the center of the next post.
In the case of floor beams, span refers to how far the beam can span before it needs support from a post or piling. For deck joists, span determines the distance a joist can cover before it needs support from a supporting beam.
When framing a roof, rafter span is determined by how far dimensional lumber can travel from the top of a wall plate to the roof peak and still provide adequate support for the roof.
What Factors Impact How Far a 2×6 Can Span?
Maximum span depends on a wide variety of factors that go beyond the simple dimension of the lumber. Wood species and quality as well as the load the structural lumber is carrying, all impact how far a 2×6 can safely span.
In this section, we’ll examine how these factors affect the maximum span of 2×6 lumber.
Wood has different strength qualities depending on what species it is. Southern pine, perhaps the most common wood used for dimensional lumber, is stronger than other softwoods, such as cedar, redwood, douglas fir, and red pine.
Thus, it’s able to span a longer distance before needing additional support.
A two-ply 2×6–2x6s are typically doubled up when used as support beams–length of yellow pine can span up to 6 feet 8 inches from post to post on a deck with joists that span 6 feet from beam to beam. Cedar and redwood, in comparison, can only span up to 5 feet 2 inches on a deck with 6-foot joist spans.
Even wood that is the same species isn’t all created equal. As anyone who’s ever dug through a pile of 2x4s or 2x6s at the home improvement store knows, the quality of wood can vary pretty significantly from one board to the next.
Since dimensional lumber used for structural framing is so critical to the safety of the structure, lumber has different levels of quality. Lumber rated No. 2 is the lowest quality with numerous knots through the board and weakest structural integrity.
No. 1 has fewer knots than No. 2 lumber and is therefore stronger. Select Structural is the highest grade of lumber, offering superior strength. How does this affect the span? Although the impact isn’t dramatic, there is a difference.
Returning to our deck framing example, No. 2-grade 2×6 joists can span up to 10 feet 9 inches from beam to beam when spaced the standard 16 inches apart with a maximum live load of 30 inches per square foot. In comparison, No.-1 grade lumber can span slightly further to 10 feet 11 inches under the same parameters. Select Structural lumber, meanwhile, can span up to 11 feet 4 inches.
While the differences may seem nominal, keep in mind that the amount of distance a beam can span can determine the number of beams and support posts you need to install, impacting the amount of time and money it takes to complete a project.
Depending on use, some 2x6s must support more loads than others. A joist on a deck or floor may support more weight than a roof rafter because it must handle a greater load. A rafter, however, in northern climates may need to be stronger to support heavy snow loads.
A 2×6 functioning as a deck beam carries a greater load than a 2×6 deck joist as it supports all the framing and decking of a deck or floor. Decking, meanwhile, has a short span because it is placed horizontally versus vertically.
How does load affect span? The greater the load it must support, the shorter the distance a 2×6 can span before needing additional support.
The load is delineated by two types: dead load and live load. Dead loads are static forces that remain constant. In the case of rafters, the dead load would be the weight of the roof it’s supporting. In the case of a deck beam, it refers to the weight of the joists and decking above it.
Live load refers to occupancy. In the case of a deck, this would be the weight of people and pets on top of the deck. For a deck with a maximum live load of 40 pounds per square foot and a dead load of 10 pounds per square foot (for a total load of 50 pounds per square foot), the maximum span is 9 feet 5 inches for a No. 1 quality 2×6 joist spaced 16 inches apart.
That span decreases as load increases. An increase in max load capacity to 60 pounds per square inch decreases the max span of a 2×6 joist to 8 feet 3 inches.
How Much Weight Can a 2×6 Support Horizontally?
A 2×6 can support up to 50 pounds per square foot of weight without sagging with a maximum span of about 12 feet when spanning a distance horizontally, with the 2×6 standing in a vertical position. This number includes both live and dead weight.
Keep in mind that the span length is a significant factor when determining how much weight the 2×6 can support. A greater span will decrease that weight, while a shorter span will increase it.
How Far Can a 2×6 Span Without Support
How far a 2×6 can span depends on the function it’s performing. Remember, span depends on multiple factors, including the amount of weight it’s supporting. With that in mind, the maximum span can vary depending on whether the 2×6 is supporting a roof, decking, or the entire framework of a floor.
Below, we’ll delve deeper into the maximum distance a 2×6 can span based on its use in common structural applications.
How Far Can a 2×6 Rafter Span?
A 2×6 rafter can span 14 feet 8 inches when spaced 16 inches apart with No. 1-grade southern pine lumber on a roof with a 3/12 slope or less with a maximum live load of 20 pounds per square foot and a dead load of 15 psf.
This may sound a little complicated, so let’s break down what impacts the span when it comes to roof rafters. As discussed above, the amount of weight the roof is carrying is part of the equation. This includes not only the sheathing and shingles resting on top of it but also any drywall attached to the underside of it.
Keep in mind that a roof must support a live load when someone needs to be on the roof for roof maintenance. The typical dead load of a roof is about 15 pounds per square foot for standard asphalt shingles but can be near twice that for heavier roofing, such as clay tiles.
A roof must also support an additional live load of about 20 psf, giving the total load for a standard asphalt roof at 35 psf. Keep in mind that if you live in a region with significant snowfall, the roof needs to be stronger as a few feet of snow can easily exceed those parameters.
In addition to load, the angle of the roof plays a role in determining the maximum span. A roof with a 3/12 or greater slope can handle longer spans, while flatter roofs that are less than 3/12 must bear more weight and hence have a shorter span. Using the example above, 2×6 that can span up to 14 feet 8 inches on a flatter roof with a slope less than 3/12 can extend to 16 feet 4 inches on a roof with a slope greater than 3/12.
Keep in mind that the above calculations are based on standard 16-inch spacing. That span increases with smaller spacing and decreases with larger spacing.
How Far Can 2×6 Decking Span?
A decking board made up of 2x6s can span a maximum distance of 24 inches from joist to joist. Why is this so much less than other spans? The difference has to do with the positioning of the 2×6.
A 2×6 is much stronger when placed on edge. This makes sense when you consider that the board has 5.5 inches of wood to provide support for downward forces when placed on edge versus 1.5 inches when laying flat.
That said, using a 2×6 as opposed to standard 5/4 decking does offer advantages in the span. That extra 1/2-inch thickness a 2×6 has over standard decking gives it an additional 8 inches of the span.
How Far Can 2×6 Floor / Deck Joist Span?
Whether you’re using 2x6s for deck joists or floor joists in a home, they face similar loads. Both must support flooring, be it decking or floor sheathing, which affects span. As with rafters, the spacing of the floor joists also affects span.
Can I Use 2×6 for Deck Joists?
You can use 2×6 dimensional lumber as deck joists for ground level decks that don’t require a handrail. This includes decks that are 30 inches or less from the ground.
This is because handrails typically attach to the rim joists of a deck. Since 2x6s aren’t large enough to adequately withstand the lateral load applied to a handrail, it’s not a good idea to use 2×6 joists with decks that require them.
In these cases, it’s best to use a 2×8 or larger dimensional lumber for the deck’s joists.
The maximum span for a No. 1 quality 2×6 floor joist made from southern pine with a maximum load of 40 psf at standard 16-inch spacing is 10 feet 9 inches, according to the International Residential Code.
When we break this down, the variables determining floor joist span are joist spacing, load, wood species, and lumber quality.
When altering the spacing, the span changes accordingly. Using the same example above, shortening the spacing to 12 inches increases the maximum span to 11 feet 10 inches while increasing it to 24 inches shortens it to 9 feet 4 inches.
Living areas of a home can have a higher live load and hence demand shorter spans. A No. 1 southern pine 2×6 spaced at 16 inches with a total load of 50 psf has a maximum span of 9 feet 9 inches.
While the variance in different types of wood species is relatively small, it is a factor you should take into account. Whereas southern pine has a max span of 10 feet 9 inches in the example at the start of this section, that increases slightly to 10 feet 11 inches for stout Douglas fir-larch but shrinks to 10 feet 3 inches for weaker spruce pine fir.
You also need to consider wood quality. Lower quality No. 2 southern pine has a max span of only 10 feet 3 inches when used in the above example, while premium-grade Select Structural southern pine lumber boasts a maximum span of 11 feet 2 inches.
While the above parameters are fairly consistent between floor joists and deck joists, they vary, so make sure to check the proper span tables for either deck or floor joists. Deck joists generally have shorter spans than interior floor joists due to the fact that they are exposed to the elements, which can negatively impact their structural integrity over time.
How Far Can a Double 2×6 Beam Span?
A double 2×6 southern pine beam can span a maximum distance of 6 feet 8 inches when supporting joists that span 6 feet, according to International Residential Code.
Beams are unique in that their span maximums depend not only on such factors as wood species but also on the configuration of the joists they’re supporting. The longer the joist span above a beam, the fewer the total number of beams and, therefore the more weight the beam must carry.
In the example above, the maximum span of a beam shrinks to 5 feet 8 inches for joists that span 8 feet.
Keep in mind that to use 2x dimensional lumber as a beam, it should be bolted together with an identical piece of 2x lumber to create a 2-ply beam.
It’s also possible to attach three pieces together, creating 3-ply lumber to increase span maximums. For example, a 3-ply 2×6 can span a maximum distance from post to post of 7 feet 11 inches for joists that span 6 feet from beam to beam.
As with other structural applications, wood species makes a difference when it comes to 2×6 beam span. Lumber such as redwood, red pine, spruce pine, and cedar have shorter spans. A cedar 2-ply 2×6 beam has a maximum span of 5 feet 5 inches for joists spaced at 6 feet, a full foot and a half less than southern pine.
Whether you’re using 2x6s for rafters, beams, or floor joists, it’s crucial to consider what factors affect the span maximums for this type of dimensional lumber.
Weight load, spacing, wood species, and even wood quality impact just how far a 2×6 can span without support. The guidelines discussed in this article can help you ensure that the structure you build can provide a sturdy and safe framework for your deck, flooring, or roof.