Rafter size for 20′, 10′, 12′, 15′, 16′, 14′, 18′, 24′ & 30′ foot span

Rafter size for 20′, 10′, 12′, 15′, 16′, 14′, 18′, 24′ & 30′ foot span | what size rafter for 20 foot span | what size rafter do i need to span 20′, 10′, 12′, 15′, 16′, 14′, 18′, 24′ & 30′ foot | rafter size for 24 foot span | rafter size for 16 foot span | rafter size for 15 foot span | rafter size for 18 foot span | rafter size for 12 foot span.

Rafter size for 20', 10', 12', 15', 16', 14', 18', 24' & 30' foot span
Rafter size for 20′, 10′, 12′, 15′, 16′, 14′, 18′, 24′ & 30′ foot span

A rafter is sloping roof member or one of a series of sloped structural members made of wooden beams or steel that extend from the ridge or hip of roof structure to the wall plate, downslope perimeter or eave, and they are designed to support the roof load, roof shingles, roof deck and its associated loads. A pair of rafters is called a couple.

When you want to design and building a roof for house, a shed, porch, cabin, garage, or home can be a huge task. What size rafter we use, their spacing, wood species, lumber grade #1, #2, #3, to consider dead, live, wind load, and snow loads, selection of the correct species, lumber grade, and dimension of lumber for the rafter span, and decide if there will be a ceiling or loft supported by the rafters.

You have to select the correct rafter size and spacing to span the distance from hip to wall based on all the factors that affect your design.

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Standard roof rafter spacing is 12 inches, 16 inches, 19.2 inches, and 24 inches on-center, however other rafter spacing may be used which are designed by a Structural Engineer. Depending on all many factors though, 16 inches and 24 inches spaced are commonly used for most buildings. The wider the space between rafters often results in rafters of greater depth too.

Rafter size: most common size of dimensional lumber which are used as roof rafters are 2×4s, 2×6s, 2×8s, 2×10s, 2×12s and 2×14s. Thinner dimensional lumber 2×4s, 2×6s, 2×8s can span further at 12″ or 16″ on centers other hand thicker dimensional lumber, such as 2x10s, 2x12s and 2×14s can span further at 24” centers. The greater the space between rafters, the shorter the distance they can span.

In this article we know about rafter size, their span, spacing between the rafters, what size rafter do i need to span 20′, 10′, 12′, 15′, 16′, 14′, 18′, 24′ & 30′ foot. All these depending on many factors, wood species, lumber grade, variable loads, location, IRC code book.

What is roof rafter

A Roof rafter is defined as one of a series of sloped structural member typically made from wooden beams that extend from the hip or ridge to wall plate or eave, or downslope perimeter. They are designed to support the roof deck, roof shingles, and everything else that goes with the roof. Its are the traditional way to frame a roof.

Size of roof rafter

In United states, most common and standard size of roof rafter is 2×4s, 2×6s, 2×8s, 2×10s, 2×12s and 2×14s. Thinner dimensional lumber 2×4s, 2×6s, 2×8s can span further at 12″ or 16″ on centers on other hand thicker dimensional lumber, such as 2x10s, 2x12s and 2×14s can span further at 24” centers.

In UK, most common and standard size of roof rafter in mm which are used in industry is 100×47 mm, 125×47 mm, 150×47 mm, 200×47 mm, 250×47 mm, and 300×47 mm. Size of rafter describe by depth and width. Width of rafter is not less than 2 inches and depth of rafters range from 4 inches to 14 inches thick.

Roof rafter spacing

Spacing between the rafters are 12”, 16”, 19.2”, and 24” on center. In North America,
the International Residential Building Code (IRC), which is the basis of most building codes, identifies the standard spacing between rafters as 12”, 16”, 19.2”, and 24” on center. Though, most commonly used 16″ and 24″ spaced for most buildings.

Rafter size for 20′, 10′, 12′, 15′, 16′, 14′, 18′, 24′ & 30′ foot span

Roof rafter size requirements depending on wood species, lumber grade #1, #2, #3, rafter span, live and dead loads on the roof, deflection, wind and snow loads, and whether a ceiling will be attached or not.

Additional factors include slope, eave and rake overhangs, roof tie-downs, rafter support bracing, collar ties, ridge connection, roof openings, ventilation, and roof finish. Live and snow loads vary from 10 to 70psf with dead loads of 10 and 20psf and deflections of L/∆=180 and L/∆=240.

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As per general rules and guideline, for 8- 10 foot span, generally you need 2″×4″ size of rafter, for 10- 12 foot span, you need 2″×6″ size of rafter, for 14 -16 foot span, you need 2″×8″ rafter, for 18- 20 foot span, you need 2″×10″ rafter & for 24 foot span, you need 2″×6″ size of rafter placed at 16″ apart from centre.

A 2×4s size of dimensional lumber as roof rafters made of Southern pine, lumber grade #2 can allow to span 10′ 4″ at 12″ spaced on center, 9′ 0″ at 16″ spaced, and 7′ 4″ at 24″ spaced on center when Live load = 20 psf, dead load = 10 psf and deflection L/∆ = 180.

A 2×6s size of dimensional lumber as roof rafters made of Southern pine, lumber grade #2 can allow to span 15′ 7″ at 12″ spaced on center, 13′ 6″ at 16″ spaced, and 11′ 0″ at 24″ spaced on center when Live load = 20 psf, dead load = 10 psf and deflection L/∆ = 180.

A 2×8s size of dimensional lumber as roof rafters made of Southern pine, lumber grade #2 can allow to span 19′ 0″ at 12″ spaced on center, 17′ 0″ at 16″ spaced, and 15′ 0″ at 24″ spaced on center when Live load = 20 psf, dead load = 10 psf and deflection L/∆ = 180.

A 2×10s size of dimensional lumber as roof rafters made of Southern pine, lumber grade #2 can allow to span 23′ 5″ at 12″ spaced on center, 20′ 3″ at 16″ spaced, and 16′ 6″ at 24″ spaced on center when Live load = 20 psf, dead load = 10 psf and deflection L/∆ = 180.

A 2×12s size of dimensional lumber as roof rafters made of Southern pine, lumber grade #2 can allow to span 30′ 2″ at 12″ spaced on center, 23′ 10″ at 16″ spaced, and 19′ 6″ at 24″ spaced on center when Live load = 20 psf, dead load = 10 psf and deflection L/∆ = 180.

What size rafter do i need for a 24 foot span

Rafter size for 24 foot span: As per general rules and guideline, generally you will need 2″×12″ size of roof rafter for a 24 foot span which are spaced at 16″ apart on center in which 12 inch is depth of rafter and 2″ their width.

A 2″×12″ size of dimensional lumber made of southern pine, lumber grade #2 as roof rafter can allow maximum span up to 24 feet when spaced at 16″ on centre, 30 feet when spaced at 12″ on centre, and 20 feet when spaced at 24″ on centre.

How far can a 2×12 rafter span: A 2×12 rafter can span 30 feet 2 inches when spaced 12 inches apart on centre, 23 feet 10 inches at 16″ OC & 19 feet 6 inches at 24″ OC without support with best quality No. 2-grade southern pine lumber with a maximum live load of 20 pounds per square foot (lbs/ft2) and a dead load of 10 psf.

What size rafter do i need for a 30 foot span

Rafter size for 30 foot span: As per general rules and guideline, generally you will need 2″×12″ size of roof rafter for a 30 foot span which are spaced at 12″ apart on center (in which 12 inch is depth of rafter and 2″ their width) without support with best quality No. 2-grade, southern pine dimensional lumber with a maximum live load of 20psf and a dead load of 10 psf.

What size rafter do i need for a 20 foot span

Rafter size for 20 foot span: As per general rules and guideline, generally you will need 2″×10″ size of roof rafter for a 20 foot span which are spaced at 16″ apart on center (in which 10 inch is depth of rafter and 2″ their width) without support with best quality No. 2-grade, southern pine dimensional lumber with a maximum live load of 20psf and a dead load of 10 psf.

What size rafter do i need for a 18 foot span

Rafter size for 18 foot span: As per general rules and guideline, generally you will need 2″×10″ size of roof rafter for a 18 foot span which are spaced at 16″ apart on center (in which 10 inch is depth of rafter and 2″ their width) without support with best quality No. 2-grade, southern pine dimensional lumber with a maximum live load of 20psf and a dead load of 10 psf.

What size rafter do i need for a 16 foot span

Rafter size for 16 foot span: As per general rules and guideline, generally you will need 2″×8″ size of roof rafter for a 16 foot span which are spaced at 16″ apart on center (in which 8 inch is depth of rafter and 2″ their width) without support with best quality No. 2-grade, southern pine dimensional lumber with a maximum live load of 20psf and a dead load of 10 psf.

What size rafter do i need for a 15 foot span

Rafter size for 15 foot span: As per general rules and guideline, generally you will need 2″×8″ size of roof rafter for a 15 foot span which are spaced at 24″ apart on center (in which 8 inch is depth of rafter and 2″ their width) without support with best quality No. 2-grade, southern pine dimensional lumber with a maximum live load of 20psf and a dead load of 10 psf.

What size rafter do i need for a 14 foot span

Rafter size for 14 foot span: As per general rules and guideline, generally you will need 2″×6″ size of roof rafter for a 14 foot span which are spaced at 12″ apart on center (in which 6 inch is depth of rafter and 2″ their width) without support with best quality No. 2-grade, southern pine dimensional lumber with a maximum live load of 20psf and a dead load of 10 psf.

What size rafter do i need for a 12 foot span

Rafter size for 12 foot span: As per general rules and guideline, generally you will need 2″×6″ size of roof rafter for a 12 foot span which are spaced at 16″ apart on center (in which 6 inch is depth of rafter and 2″ their width) without support with best quality No. 2-grade, southern pine dimensional lumber with a maximum live load of 20psf and a dead load of 10 psf.

What size rafter do i need for a 10 foot span

Rafter size for 10 foot span: As per general rules and guideline, generally you will need 2″×6″ size of roof rafter for a 10 foot span which are spaced at 12″ apart on center (in which 6 inch is depth of rafter and 2″ their width) without support with best quality No. 2-grade, southern pine dimensional lumber with a maximum live load of 20psf and a dead load of 10 psf.

Conclusions:

As per general rules and guideline, for 8- 10 foot span, generally you need 2″×4″ size of rafter, for 10- 12 foot span, you need 2″×6″ size of rafter, for 14 -16 foot span, you need 2″×8″ rafter, for 18- 20 foot span, you need 2″×10″ rafter & for 24 foot span, you need 2″×6″ size of rafter placed at 16″ apart from centre.

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