What size lumber for 20′, 16′, 18′, 10′, 12′ & 22 feet span | lumber size for a 10 foot span | lumber size for a 16 foot span | lumber size for a 20 foot span | lumber size for 30 foot span | lumber size for 24 foot span | what size lumber to span 20 feet, 16 feet, 12 feet, 18 feet, 14 feet, 10 feet, 24 feet and 22 feet.

There are different depth of lumber as a floor joist are used in floor construction such as 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/ lumber 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 joists can be define as several small beams. Floor joists are 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.

Floor 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.

What size lumber for 20′, 16′, 18′, 12′, 22′, 24′, 25′, 26′ & 30 feet span as floor joist depending on different size of Lumber, species of wood, grade of wood, spacing between the joist, expected dead and live load of structure that coming to joist. 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.

Not all the type of species of wood/ lumber created equally strong and type of tree used to make joist affects the span allowed. 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 joist for different sizes of lumber 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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**What size lumber for 20′, 16′, 18′, 12′, 22′, 24′, 25′, 26′ & 30 feet span**

What size lumber for 20′, 16′, 18′, 12′, 22′, 24′, 25′, 26′ & 30 feet span as floor joist depending on different size of Lumber, species of wood, grade of wood, spacing between the joist, expected dead and live load of structure that coming to joist. 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.

**What size lumber for a 20 foot span**:- as per general thumb rule and guidelines, for a 20 foot span, you will need atleast 2×12 size of lumber/ floor joist when spaced at 16″ apart. Thus, a 2×12 size of lumber can allow to span 20 feet. For a 20-foot spans, the lumber has to be at least 12 inches in depth used as floor joist.

**What size lumber for a 10 foot span**:- as per general thumb rule and guidelines, for a 10 foot span, you will need atleast 2×6 size of lumber/ floor joist when spaced at 16″ apart. Thus, a 2×6 size of lumber can allow to span 10 feet. For a 10-foot spans, the lumber has to be at least 6 inches in depth used as floor joist.

**What size lumber for a 12 foot span**:- as per general thumb rule and guidelines, for a 12 foot span, you will need atleast 2×8 size of lumber/ floor joist when spaced at 16″ apart or 2×6 lumber at 12″ spaced. Thus, a 2×8 size of lumber can allow to span 12 feet. For a 12-foot spans, the lumber has to be at least 6 inches to 8 inches in depth used as floor joist.

**What size lumber for a 14 foot span**:- as per general thumb rule and guidelines, for a 14 foot span, you will need atleast 2×8 size of lumber/ floor joist when spaced at 16″ apart. Thus, a 2×8 size of lumber can allow to span 14 feet. For a 14-foot spans, the lumber has to be at least 8 inches in depth used as floor joist.

**What size lumber for a 15 foot span**:- as per general thumb rule and guidelines, for a 15 foot span, you will need atleast 2×8 size of lumber/ floor joist when spaced at 12″ apart. Thus, a 2×8 size of lumber can allow to span 14 feet. For a 14-foot spans, the lumber has to be at least 8 inches in depth used as floor joist.

**What size lumber for a 16 foot span**:- as per general thumb rule and guidelines, for a 16 foot span, you will need atleast 2×10 size of lumber/ floor joist when spaced at 16″ apart. Thus, a 2×10 size of lumber can allow to span 16 feet. For a 16-foot spans, the lumber has to be at least 10 inches in depth used as floor joist.

**What size lumber for a 18 foot span**:- as per general thumb rule and guidelines, for a 18 foot span, you will need atleast 2×10 size of lumber/ floor joist when spaced at 12″ apart. Thus, a 2×10 size of lumber can allow to span 18 feet. For a 18-foot spans, the lumber has to be at least 10 inches in depth used as floor joist.

**What size lumber for a 22 foot span**:- as per general thumb rule and guidelines, for a 22 foot span, you will need atleast 2×12 size of lumber/ floor joist when spaced at 12″ apart. Thus, a 2×12 size of lumber can allow to span 22 feet. For a 22-foot spans, the lumber has to be at least 12 inches in depth used as floor joist.

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**Conclusion**:-

For a 20 foot span, you will need atleast 2×12 size of lumber/ floor joist when spaced at 16″ apart. Thus, a 2×12 size of lumber can allow to span 20 feet. For a 20-foot spans, the lumber has to be at least 12 inches in depth used as floor joist.