A habitable space would be a loft or other area where people might sleep or live – or both. How Far Can You Span a 2×4 Ceiling Joist?Ĭeiling joist span tables have two different categories: habitable and uninhabitable. If you have that spacing for a roof with 2×4 rafters, then you can have a maximum span of 10’3” and 8’11”, respectively, if using SYP select grade lumber. Most roofs have rafters spaced further than 12” apart – usually 16” or 24” on center. While no reason is given, one can assume that using a 2×4 rafter in that instance is likely not acceptable and should be avoided.
Span tables that indicate maximum rafter lengths for roofs with slopes lower than 3:12 do not include 2×4 lumber. Therefore all spans mentioned in this section should assume a slope of at least 3:12. While no minimum slope is given, many span tables differentiate rafter span lengths between roofs sloped 3:12 and greater versus lower slopes. How Far Can a 2×4 Rafter Span?Ģ×4 rafters spaced at 12” on center can span up to 11’ 3”, for select grade SYP. For small projects, using stronger lumber like SYP versus Redwood could allow you to have a larger shed or platform. The differences in wood species are significant, and you need to know the type of wood you are using to properly read and use a span table. A redwood joist with the same spacing will span 6’ 6” – 9” less than an SYP joist at the same spacing.
If you have Spruce-pine-fir lumber, then your span changes to 6’ 8” for 16” joist spacing. These calculations assume a 30 psf live load. If you opt to space your 2×4 joists at 24” on center, then you can only span a distance of 6’ 4”. This assumes that the joist is not cantilevered and terminates with support on either end. If you opt to space your 2x4s at 16” on center, then your maximum span will be 7’ 3” with SYP. Instead, using a 2×4 joist would be more practical in a very small shed or platform coming off a deck. The loads and spans would simply be too great, and the amount of wobble and bounce would be drastic. Realistically, you are not going to use a 2×4 for floor joists in your home. Living areas and decks require a minimum of 40 psf for support, so a 2×4 joist, in this instance, could only be for a shed or other non-living space.
Also, this span is for 30 pounds per square foot of live load. However, this span is for Southern Yellow Pine, which is one of the strongest softwoods available. How Far Can 2×4 Floor Joist Span?Ī 2×4 floor joist spans up to 7’ 11” when spaced 12” apart, on center. The highest grade – select – will have few to no knots or imperfections, hence the greater load-bearing capability. While your typical span table defaults to number 2 grade lumber, higher grades such as number 1 or select will hold more weight. SYP can span greater lengths than Redwood or SPF, so know what you are buying. If you are out west, then you’ll be purchasing Redwood or SPF – Spruce Pine or Fir. In the South, you’ll be buying SYP – Southern Yellow Pine. Most people will only have one choice and it depends on where you live. Many different species of tree are used for dimensional lumber. The actual length of the wood will be longer because it has to sit on something to support itself. “Span” refers to the distance between the inside of the two bearing points of a piece of horizontal lumber. It is important to know the definition of the term “span” when talking about lumber and framing. A single 2×4 is never used for a girder because it cannot bear the loads required when framing a structure. In a span table, you can only find information for a doubled 2×4 beam – also called a girder. Other commonly available species of dimensional lumber span slightly less distance, such as SPF, which can only span 6’ 1”.