What size ceiling joist do you need for 10′, 12′, 14′, 16′, 20′ & 24 foot span depends on several factors like grade & species of wood, load, span, construction requirements and building code.

There are different depth of ceiling joist are used in floor construction such as 2×4, 2×6, 2×8 and 2×10 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.

Ceiling joists provide support for more than one surface in your home. The first surface is, unsurprisingly, the ceiling, the materials of which attach directly to the joists. The other surfaces are the walls, which the joists span the distance between, providing a source of support to keep the walls from shifting.

Ceiling joists are a critical element of a house’s structure. They not only support the weight of the ceiling material, but also bear the outward pressure that is placed on exterior walls from the weight of the roof. The spacing and allowable span of ceiling joists in residential construction is standardized according to building codes, which cover not only basic wall-to-wall room design but nonparallel ceiling joist construction as well.

Ceiling 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 ceiling joist for 10′, 12′, 14′, 16′, 20′ & 24 foot span 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.

Not all the type of species of wood 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 ceiling 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.

A #2-SPF 2×6 ceiling joist can allow to span 15 feet and 2 inches at 12″ oc, 13 feet and 9 inches at 16″ oc and 12 feet and 0 inches at 24″ oc.

A #2-SPF 2×8 ceiling joist can allow to span 19 feet and 1 inch at 12″ oc, 18 feet and 2 inches at 16″ oc and 15 feet and 10 inches at 24″ oc.

A #2-SPF 2×10 ceiling joist can allow to span 25 feet and 5 inches at 12″ oc, 23 feet and 2 inches at 16″ oc and 20 feet and 2 inches at 24″ oc.

A #2-SPF 2×4 ceiling joist can allow to span 9 feet and 8 inches at 12″ oc, 8 feet and 9 inches at 16″ oc and 7 feet and 8 inches at 24″ oc.

**What size ceiling joist for 10′, 12′, 14′, 16′, 20′ & 24 foot span**

In general, the size of ceiling joists for a 10 to 12-foot span need to be 2×4 lumber, while the size of ceiling joists for a 12 to 15-foot span need to be 2×6 lumber. Likewise, the size of ceiling joists for a 15 to 19-foot span need to be 2×8 lumber, while the size of ceiling joists for a 20 to 25-foot span need to be 2×10 lumber.

**What size ceiling joist for a 10′**

Typically for a 10 foot span you would need 2″×4″ size of ceiling joist made of #2 spruce – pine- fir when spaced 12 inches on center. Thus, a #2-SPF 2″×4″ size of ceiling joist can allow to span a maximum of 10 feet when spaced 12 inches apart with maximum ceiling loads are assumed to be 20 PSF and roof pitch is not steeper than 3 in 12.

**What size ceiling joist for a 12′**

Typically for a 12 foot span you will need 2″×6″ size of ceiling joist made of #2 spruce – pine- fir when spaced 24 inches apart. Thus 2″×6″ size of ceiling joist made of #2 spruce – pine- fir can allow span up to 12 feet when spaced 24 inches apart with maximum ceiling loads are assumed to be 20 PSF and roof pitch is not steeper than 3 in 12.

**What size ceiling joist for a 14′**

Typically for a 14 foot span you will need 2″×6″ size of ceiling joist made of #2 spruce – pine- fir when spaced 16 inches apart. Thus 2″×6″ size of ceiling joist made of #2 spruce – pine- fir can allow span up to 14 feet when spaced 16 inches apart with maximum ceiling loads are assumed to be 20 PSF and roof pitch is not steeper than 3 in 12.

**What size ceiling joist for a 15′**

Typically for a 15 foot span you will need 2″×6″ size of ceiling joist made of #2 spruce – pine- fir when spaced 12 inches apart. Thus 2″×6″ size of ceiling joist made of #2 spruce – pine- fir can allow span up to 15 feet when spaced 12 inches apart with maximum ceiling loads are assumed to be 20 PSF and roof pitch is not steeper than 3 in 12.

**What size ceiling joist for a 16′**

Typically for a 16 foot span you will need 2″×8″ size of ceiling joist made of #2 spruce – pine- fir when spaced 24 inches apart. Thus 2″×8″ size of ceiling joist made of #2 spruce – pine- fir can allow span up to 16 feet when spaced 24 inches apart with maximum ceiling loads are assumed to be 20 PSF and roof pitch is not steeper than 3 in 12.

**What size ceiling joist for a 18′**

Typically for a 18 foot span you will need 2″×8″ size of ceiling joist made of #2 spruce – pine- fir when spaced 12 inches apart. Thus 2″×8″ size of ceiling joist made of #2 spruce – pine- fir can allow span up to 18 feet when spaced 12 inches apart with maximum ceiling loads are assumed to be 20 PSF and roof pitch is not steeper than 3 in 12.

**What size ceiling joist for a 20′**

Typically for a 20 foot span you will need 2″×10″ size of ceiling joist made of #2 spruce – pine- fir when spaced 24 inches apart. Thus 2″×10″ size of ceiling joist made of #2 spruce – pine- fir can allow span up to 20 feet when spaced 24 inches apart with maximum ceiling loads are assumed to be 20 PSF and roof pitch is not steeper than 3 in 12.

**What size ceiling joist for a 24′**

Typically for a 24 foot span you will need 2″×10″ size of ceiling joist made of #2 spruce – pine- fir when spaced 12 inches apart. Thus 2″×10″ size of ceiling joist made of #2 spruce – pine- fir can allow span up to 24 feet when spaced 12 inches apart with maximum ceiling loads are assumed to be 20 PSF and roof pitch is not steeper than 3 in 12.

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**Conclusion**:-

Typically for a 10 foot span you will need 2″×4″ size of ceiling joist made of #2 spruce – pine- fir when spaced 12 inches apart, for a 12 foot 2×6@24″C/C, for a 14 foot 2×6@16″C/C, for a 16 foot 2×8@24″C/C, for a 20 foot 2×10@12″C/C and for a 24 foot span you will need 2×10@12″C/C size of ceiling joist.