Floor joists can span different lengths depending on the depth of the joist. A 2×12 floor joist can span far more than a 2×6 or 2×8 floor joist.
You need to know the right span length for joist while building a deck, adding a second story to your house, having a room addition, or adding a large bath tub.
So, there’re a lot of times when homeowners or craftsman are finding difficulty in knowing the right length of a floor joist can span without any intermediate support.
So, here’s a detail guide about floor joist spacing along with a chart so you can easily pick suitable size of floor joist depending on the spanning requirements:
Different sizes of floor joists
Floor joists are horizontal structural member of the floor framing that span an open space between end beam. Joists transfer the floor framing load to the vertical members and provide stiffness to the subfloor sheathing. They are like a horizontal diaphragm that keeps the floor framing intact.
The most common type of floor joist is solid lumber. But I-shaped or open web floor joists are also common among homeowners in special conditions.
Problems:
- If you have a floor bouncing or sagging from different spots; you might have a broken floor joist.
- If you hear loud squeaking sound while walking on the floor, there’re some issues with floor joists.
Note: Installing floor joists is not a DIY project for beginners. It needs a good knowledge of fixing and installing framing elements of a home. Floor joists being a load bearing and structural member of your home, requires a structural engineer or a professional contractor for installation.
Also Read: Ridge beam – Size – Definition – Span – Span Table – Calculator
Floor joist spacing
The spacing of floor joists in framing drawings are specified as center-to-center or (o.center) spacing between adjacent joists. Most common spacing in United States for typical floors is 16 inches apart.
But it may vary depending on the loading condition and type of building. Some building code may also need specific provisions to distribute the load of a structure as per local soil conditions.
Also Read: What is a 8 on 12 roof pitch – 8/12 roof pitch (with Calculator)
Floor joist Span
The span of floor joists is the linear distance that a joist will span from one end to the other without any intermediate support. Floor joist span depends on a lot of factors like joist size, loading condition, lumber grade, and wood species. The over to center spacing of floor joist also affects the span of the joist.
Whether you’re hiring an expert for a framing job or are working as a DIYer; it is critical to choose the right joist span for your home. Designers calculate the span lengths so the permits can be easily issued.
The trick: a floor joist that has more load-carrying capacity can span on longer lengths.
Large floor joists with more depth and spaced closer can span more.
The best approach in picking the right size of floor joist is to maximize the span and spacing. That’s one way of getting economical design and optimizing material usage.
Floor joist span depends on a lot of factors like:
Wood species
Species with more growth rings per inch are stronger. Slow growing species are stronger than fast growing species. Typical species are red cedar, white pine, yellow pine, Douglas fir, Hemlock, redwood, and ponderosa pine. Douglas fir and Southern yellow pine are stronger.
Also Read: Glulam Beam – Advantages – Applications – Table (With Examples)
Grade of the lumber
Lumber pieces with fewer flaws can span longer, as they are stronger overall. 1 grade lumber or 2-grade lumber are ideal for framing works. Don’t use 3 or 4 grade lumber for structural framing applications.
Width and thickness of the boards
Lumber size including top-to-bottom width is an important factor along with thickness. A joist with 2-2x6s can span more than a single 2×6. But you can even span more with 2×12 as you can achieve with double 2x6s.
Spacing between joists
With joists placed closer to one-an-other you can increase the span size.
The span depends a lot of the purpose of your floor or the loading it is subjected to. Both dead and live load needs to be considered for floor framing. The dead load is the total load of building elements distributed over square footage of the area. The live load is the weight of furnishings, occupants and any other items to be stored on the top. Typical live load for buildings is 30 to 40 pounds per square foot (psf).
- Garage floor live load – 50 psf or higher
- Attic space – inaccessible – 20 psf
- First floor live load – 40 psf
- Second floor live load – 30 psf
- Dead load : 10 psdf
Chart
Here’s a floor joists span table / chart for your guide;
- First pick up the wood specie you’re using.
- Then try to finalize the o.c. spacing of the joists or the size to get the span.
| Joist span | Joist spacing | |||||
| Joist Size | 16″ o.c. | 24″ o.c. | 16″ o.c. | 24″ o.c. | 16″ o.c. | 24″ o.c. |
| 2×6 | 9′ 9″ | 8′ 3″ | 8′ 8″ | 7′ 6″ | 7′ 6″ | 6′ 3″ |
| 2×8 | 12′ 8″ | 10′ 8″ | 11′ 0″ | 10′ 2″ | 10′ 5″ | 8′ 6″ |
| 2×10 | 16′ 0″ | 13′ 0″ | 14′ 6″ | 12′ 4″ | 12′ 9″ | 10′ 5″ |
| 2×12 | 18′ 6″ | 15′ 0″ | 17′ 6″ | 14′ 4″ | 14′ 9″ | 13′ 0 |
| Joist Species | Yellow Pine, Douglas Fir | Redwood Hemlock, Spruce | Western red cedar, Eastern white pine |
Also Read: Bond beam in masonry walls – Design – Size – Foundation – Pros & Cons
How far can 2×6 floor joist span?
For typical 16” o.c. spacing ; a 2×6 (2-by-6) floor joist can span 9 feet and 9 inches with grade-1 high quality yellow pine or Douglas fir. Whereas, with Redwood hemlock or western red cedar, the span will be on lower side i.e. around 8 feet 8 inches or 7 feet 6 inches.
How far can 2×8 floor joist span?
For typical 16” o.c. spacing ; a 2×8 (2-by-8) floor joist can span 12 feet and 8 inches with grade-1 high quality yellow pine or Douglas fir. Whereas, with Redwood hemlock or western red cedar, the span will be on lower side i.e. around 11 feet 0 inches or 10 feet 5 inches.
How far can 2×10 floor joist span?
For typical 16” o.c. spacing ; a 2×10 (2-by-10) floor joist can span 16 feet s with grade-1 high quality yellow pine or Douglas fir. Whereas, with Redwood hemlock or western red cedar, the span will be on lower side i.e. around 14 feet 6 inches or 12 feet 9 inches.
How far can 2×12 floor joist span?
For typical 16” o.c. spacing ; a 2×12 (2-by-12) floor joist can span 18 feet and 6 inches with grade-1 high quality yellow pine or Douglas fir. Whereas, with Redwood hemlock or western red cedar, the span will be on lower side i.e. around 17 feet 6 inches or 14 feet 9 inches.
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