How far can a 2×6, 2×8, 2×10 and 2×12 floor joist span depends on several factors like grade & species of wood, building code, loads and construction requirements.

There are different depth of floor joist are used in floor construction such as 2×4, 2×6, 2×8, 2×10 and 2×12 made of different species of wood (southern yellow pine & Douglas fir) and different grade such as grade – 1, grade – 2, grade – 3. Southern yellow pine is strongest species of wood that can span more distance compared to other species of wood. Grade 1 lumber have higher strength than other grade Lumber due to fewer knots.

Floor and roof joists can be define as several small beams. It is typically a horizontal structural member that runs across an open space of building on supporting wall or studs. Their function is similar as beams, except floor joists are supported by wall, foundations, or beams framing.

Joists usually run between walls or rafters to support a ceiling or floor. They transfer the dead load of the subfloor and floor finishes and live load of people, furniture and furnishings to beams, walls, headers, or foundation walls.

It is like the skeleton/ framing of a building that supports the load which the floor is built to bear. Joists are technically beams that typically spans relatively short distances compared to beams and are made of wood, steel, or engineered wood or lumber.

The loading includes dead load of the weight of the frame structure & fixed weight and live load of People, furniture, appliances and a snow on the roof.

Southern yellow pine is strongest species of wood that can span more distance compared to other species of wood. Grade 1 lumber have higher strength than other grade Lumber due to fewer knots.

Spacing between floor and flat roof joist for different sizes are kept at 12 inches, 16 inches and 24 inches apart. The joist which are kept at lower spacing can allow longer distance to span as compared to joist spaced further apart. Standard spacing between floors joist is 16 inches.

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**How far can a 2×6, 2×8, 2×10 and 2×12 floor joist span**

The thumb rule for the depth of common floor joists is to take half span in feet; to this number add 2 for the depth of the joist in inches. Example, for a 18 Feet span, half this is 9, add 2, which gives 11 inches for the depth. So a 2×12 floor joist will be required. it’s important to use the actual engineered wood dimensions, not the nominal dimensions).

In general, the maximum span for a 2×6 floor joist is typically about 8 feet, while the maximum span for a 2×8 floor joist is typically about 12 feet. Likewise, the maximum span for a 2×10 floor joist is typically about 16 feet, while the maximum span for a 2×12 floor joist is typically about 18 feet.

In general, a 2×6 floor joist can span from a 7 to 11 foot, whereas a 2×8 floor joist can span from a 9 to 14 foot. Moreover, a 2×10 floor joist can span from a 11 to 18 foot, whereas a 2×12 floor joist can span from a 13 to 20 foot.

**2×8 joist span**

The maximum span for a #2-SP 2×8 lumber at 16″ spacing, L/360 deflection and 40 psf live load is typically about 11 feet and 4 inches.

A #2-SPF 2×8 floor joist can span a maximum distance of 11′-4″, a #2 HFir (hemlock-fir) can span 12′0″, and #2 SYP (southern yellow pine) can span 12′4″ when 40 pounds live load and 10 lb dead load at 16″ o.c. L/360 deflection.

**2×6 joist span**

A 2×6 joist spaced 16 inches apart can span a maximum distance of 10 feet 9 inches when when 40 lb live load and 10 lb dead load at 16″ o.c. L/360 deflection.

**2×10 joist span**

A 2×10 joist spaced 16 inches apart can span a maximum distance of 16 feet 0 inches when 40 lb live load and 10 lb dead load at 16″ o.c. L/360 deflection.

**2×12 joist span**

A 2×12 joist spaced 16 inches apart can span a maximum distance of 18 feet 0 inches when when 40 lb live load and 10 lb dead load at 16″ o.c. L/360 deflection.

**2×6 floor joist span**

As per international residential code, A 2×6 floor joist, No. 1 quality, made from southern pine will span 10 feet 9 inches when load of 40 psf at standard 16-inch spacing.

**How far can a 2×6 floor joist span**

Typically a 2×6 floor joists can span from 8 to 10 feet from beam to beam when spaced the standard 16 inches apart with a maximum residential floor loads are assumed to be 50 pounds per square foot (40 pounds live plus 10 pounds dead).

**2×8 floor joist span**

As per international residential code, the maximum span for a No. 1 quality 2×8 floor joist made from southern pine with a maximum load of 50 psf at standard 16-inch spacing is 12 feet 0 inches.

**How far can a 2×8 floor joist span**

As per general thumb rules and guideline, joist made of southern pine or Douglas Fir by using grade #1 or #2, a 2×8 floor joists can span up to 12 feet from beam to beam when spaced the standard 16 inches apart with a maximum residential floor loads are assumed to be 50 pounds per square foot (40 pounds live plus 10 pounds dead).

**2×10 floor joist span**

As per international residential code, the maximum span for a No. 1 quality 2×10 floor joist made from southern pine with a maximum load of 50 psf at standard 16-inch spacing is 16 feet 0 inches.

**How far can a 2×10 floor joist span**

As per general thumb rules and guideline, joist made of southern pine or Douglas Fir by using grade #1 or #2, a 2×10 floor joists can span up to 16 feet from beam to beam when spaced the standard 16 inches apart with a maximum residential floor loads are assumed to be 50 pounds per square foot (40 pounds live plus 10 pounds dead).

**2×12 floor joist span**

As per international residential code, the maximum span for a No. 1 quality 2×12 floor joist made from southern pine with a maximum load of 50 psf at standard 16-inch spacing is 18 feet 0 inches.

**How far can a 2×12 floor joist span**

As per general thumb rules and guideline, joist made of southern pine or Douglas Fir by using grade #1 or #2, a 2×12 floor joists can span up to 18 to 20 feet from beam to beam when spaced the standard 16 inches apart with a maximum residential floor loads are assumed to be 50 pounds per square foot (40 pounds live plus 10 pounds dead).

**Conclusions**:-

Joist made of southern pine or Douglas Fir by using grade #1 or #2, a 2×6 floor joists can span up to 10 feet, 2×8 upto 12 feet, 2×10 upto 16 feet and 2×12 upto 20 feet from beam to beam when spaced the standard 16 inches apart with a maximum residential floor loads of 50 PSF.