The size of rafters you need depends on several factors such as the span of roof, construction requirements, pitch of roof, load, grade and species of wood, local building codes and on your specific requirements and local regulations.
The International Residential Code (IRC) specifies that roof rafter spacings need to be 12″, 16″, 19.2″, and 24″ on center. The common sizes of American Softwood dimensional lumber used for roof rafters include 2×4, 2×6, 2×8, 2×10, and 2×12.
Typically, a 2×4 size rafter can allow to span from 6 to 9 feet, while a 2×6 rafter can allow to span from 10 to 12 feet. Moreover, a 2×8 size rafter can allow to span from 13 to 15 feet, whereas a 2×10 rafter can allow to span from 16 to 20 feet. In addition, a 2×12 rafter can allow to span from 21 to 27 feet.
In the field of construction of wooden framing structure, rafters are a series of sloped structural member that will extend from a ridge of the roof or hip to the top wall plate, or downslope perimeter or an eave. They are made from various species of wood and that are designed to support the roof shingles, roof deck, roof covering and are used to support the load of the building, normally the roof area.
American Softwood dimensional lumber 2×4, 2×6, 2×8, 2×10, and 2×12 made from different grade and species of wood like grade #1 and grade #2 of Southern yellow pine (SYP), Douglas Fir (DF), Hem Fir (HF) and Spruce pine fir (SPF) are used to provide timber which have much strength. In US, most wood rafters have maximum length of 20 feet. A wooden framing house very much popular in North region of United states, Canada and United Kingdom.
In general, the roof rafter span is typically measured by the distance of the rafter projection horizontally from the ridge or hip to the supporting outside top wall plate’s or an eave. The roof rafters span may be either 10 feet, 12 feet, 14 feet, 15 feet, 16 feet, 18 feet, 20 feet, 22 feet, 24 feet, 27 feet and so on higher. In this article you know about what size rafters do i need for a specific span that will help you in better understanding and to figure out or estimate of rafter size and their depth according to span.
What size rafters do i need for a specific span (10′, 12′, 14′, 15′, 16′, 18′, 20′, 22′, & 24 feet)
In general, the size of a rafter for a 6 to 9-foot span you need to be 2×4 lumber, while for a 10 to 12-foot span, you can typically use 2×6 lumber. Likewise, for a 13 to 15-foot span, you would need 2×8 rafters, while for a 16 to 20-foot span, you can typically use 2×10 rafters. In addition, for a 21 to 27-foot span, the rafter size need to be 2×12 dimensional lumber.
What size rafters do i need?The size of rafters you need depends on several factors. However, as rough guidelines, for a 10 to 12-foot span, using 2×6 dimensional lumber at 16″ O.C would typically be suitable for residential construction.
What size rafter do i need for a 10 foot span
The size of the rafter you need for a 10 foot span should be 2″×6″ dimensional lumber which spaced at 16 inches on center. So, a 2×6 lumber at 16″ oc is appropriate size of rafter needed to span 10 feet is often suitable for standard residential applications.
What size rafter do i need for a 12 foot span
The rafter size for a 12-foot span need to be 2×6 dimensional lumber (measure 2-inches wide by 6-inches deep), which spaced at 16 inches OC. So, a 2×6 lumber is good size of rafter needed to span 12 feet is often suitable for standard residential applications.
What size rafter do i need for a 14 foot span
The rafter size for a 14-foot span need to be 2×8 dimensional lumber (measure 2-inches wide by 8-inches deep), which spaced at 16 inches OC. So, for 14 feet span, using common construction lumber such as SPF (Spruce-Pine-Fir) or similar, a 2×8 rafter size is used for residential applications.
What size rafter do i need for a 15 foot span
Typically the rafter size required for a 15 foot span need to be 2×8 dimensional lumber spaced at 16 inches oc. This includes the 8 inches is nominal depth and 2 inches is the width. So, a 2×8 lumber at 16″ oc is appropriate size of rafter needed to span 15 feet.
What size rafter do i need for a 16 foot span
Typically the rafter size required for a 16 foot span need to be 2×10 dimensional lumber spaced at 16 inches oc. This includes the 10 inches is nominal depth and 2 inches is the width. So, a 2×10 lumber at 16″ oc is appropriate size of rafter needed to span 16 feet.
What size rafter do i need for a 18 foot span
The size of rafter needed for a 18 foot span have to be 2×10 dimensional lumber (measure 2-inches wide by 10-inches deep), which spaced at 16 inches OC. So, the size of the rafter you need to span 18 feet ought to be something like 2×10 lumber or larger is often suitable for standard residential applications.
What size rafter do i need for a 20 foot span
The common rafter size needed for a 20 foot span have to be 2×10 dimensional lumber spaced at 16 inches O.C. This includes the 10 inches is nominal depth and 2 inches is the width. So, a 2×10 lumber at 16″ OC is appropriate size of rafter needed to span 20 feet.
What size rafter do i need for a 22 foot span
The size of the rafter you need to span 22 feet ought to be something like 2×12 lumber or larger at 16 inches on center. So, for a 22 foot span, the size of rafter should be 2×12 lumber is often suitable for standard residential applications.
What size rafter do i need for a 24 foot span
The size of rafter needed for a 24 foot span have to be 2×12 dimensional lumber (measure 2-inches wide by 12-inches deep), which spaced at 16 inches OC. So, the size of the rafter you need to span 20 feet ought to be something like 2×12 lumber.
What size rafter do i need for a 26 foot span
However, as a general guideline, for a span of a 26 foot, a rafter size of around 2×12 dimensional lumber (measure 2-inches wide by 12-inches deep), which spaced at 16 inches on center might be considered, but this is a very rough estimate and should not be used for actual construction without professional analysis.
Conclusions:-
In general, the size of rafter you need for a wooden frame house should be 2″×4″ lumber for a 6 to 9-foot span, 2″×6″ rafter for a 10 to 12-foot span, 2″×8″ rafter for a 13 to 15-foot span, 2″×10″ rafter for a 16 to 20-foot span, and 2″×12″ rafter for a 21 to 27-foot span.