Rafter size for 10′, 12′, 15′, 16′, 18′, 20′ & 24 foot span | rafter size for 10 foot span | rafter size for 12 foot span | rafter size for 15 foot span | rafter size for 16 foot span | rafter size for 18 foot span | spacing of roof rafter | what size rafter do i need to span 10′, 12′, 15′, 16′, 18′, 20′ & 24 foot span.
A rafter is a structural component build of wood or steel that is used as part of a roof construction. Rafter runs from the ridge or hip of the roof to the wall plate of the external wall. Rafters are generally provide in series, side by side, providing a plateform to support roof decks and roof coverings.
In many countries such as in US, Canada United Kingdom roof rafter made of wood/ timber are much common to build a house. Many species of wood are used to provide timber which have much strength. Rafters are usually made of pine or cedar tree, for longer span rafters, building materials several manufacturers have created Laminated veneer lumber (LVL) rafters that can be 2–5 times longer than typical wood rafter. In US, most wood rafters have maximum length of 20 feet.
What size lumber for roof rafters:- most common size of dimensional lumber for roof rafters are 2″×6″, 2″×8″, 2″×10″, 2″×12″ and 2″×14″ used in roof framing. Thicker dimensional lumber, such as 2x10s and 2x12s can span further. Thickness of rafter should be not less than 2 inches and their depth should be range from 4″ to 12″. Length of Rafter depending on climatic condition, style, slope and type of structure. It is used over brick external wall, wall plate, over two support and over top of beam.
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Rafter size for 10, 12, 15, 16, 18 , 20 & 24 foot span
A rafter is a structural component that is used as part of a roof construction. Typically, it runs from the ridge or hip of the roof. Design and construction of roof is depending on many factors but one of the most common important factor is climatic and weather condition of your surrounding areas, in your cities and countries. The area which has heavy rainfall and snowfall require good drainage for roof, roof drainage depending on slope of the roof provided, based on slope of roof it is categorised into two types flat roof and pitched roof or sloping roof.
The spacing of roof rafter is just one of the component used to determine the minimum size of roof rafter. There is no any standard rafter spacing measurements. But generally rafter spaced typically either 12, 16 or 24 inches apart in one of several industry -standard increments.
In this article you know about Rafter size for 10 foot, 12 foot, 15 foot, 16 foot & 18 foot span that will help you in better understanding and to figure out or estimate of rafter size and their depth according to span. Generally span is distance between two support end.
Roof rafter spacing
Most standard, roof rafter spacing is 16 inches apart on center, but this can vary depending on building codes and the requirements of the structure. So, 12 inches, and 24 inches apart on centre are also used. Roof rafter help distribute the load of a structure. The rafter which are kept at lower spacing can allow longer distance to span as compared to rafter spaced further apart.
What size Rafter do i need for a 10, 12, 15, 16 & 18 foot span
The size of Rafter will depends on varieties of factors such as thickness of roof sheathing, boards, snow load, live load, species of wood, grade of timber, pitch of roof including the span and spacing of timber. Generally 2″×6″ rafter can span upto 10 to 15 foot, 2″×8″ rafter can span upto 13 to 19 foot, 2″×10″ rafter can span upto 16 to 23 foot, 2″×12″ rafter can span upto 18 to 27 foot and 2″×4″ rafter can span upto 7 to 9 foot based on normal weight condition, spacing between rafter, species and grade of timber and pitch or slope roof.
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Rafter size for 10 foot span
Aa per general rules and guidelines, rafter made of pine wood, for a 10 foot span, size of rafter should be 2″×4″ or 2″×6″ in which thickness of rafter is 2″ and their depth range from 4 inches to 6 inches. Thus, you need 2″×6″ size rafter placed at 24″ OC for a 10 foot span on normal weight, live load of 40lb/ ft2 and by using pine wood with no. 1 grade lumber.
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Rafter size for 12 foot span
As per general rules and guidelines, rafter made of pine wood, for a 12 foot span, size of rafter should be 2″×6″ in which thickness of rafter is 2″ and their depth range is 6 inches. Thus, you need 2″×6″ rafter, placed at 16″ OC are sufficient and better option for you to provide allowable span upto 12 foot for providing great stability for your projects.
Rafter size for 15 foot span
As per general rules and guidelines, rafter made of pine wood, for a 15 foot span, size of rafter should be 2″×8″ in which thickness of rafter is 2″ and their depth range is 8 inches. Thus, you need 2″×8″ rafter, placed at 16″ OC are sufficient and better option for you to provide allowable span upto 15 foot for providing great stability for your projects.
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Rafter size for 16 foot span
As per general rules and guidelines, rafter made of pine wood, for a 16 foot span, size of rafter should be 2″×8″ in which thickness of rafter is 2″ and their depth range is 8 inches. Thus, you need 2″×8″ rafter, placed at 16″ OC are sufficient and better option for you to provide allowable span upto 16 foot for providing great stability for your projects.
Rafter size for 18 foot span
As per general rules and guidelines, rafter made of pine wood, for a 18 foot span, size of rafter should be 2″×10″ in which thickness of rafter is 2″ and their depth range is 10 inches. Thus, you need, 2″×10″ rafter placed at 16″ OC are sufficient and better option for you to provide allowable span upto 18 foot for providing great stability for your projects.
Rafter size for 20 foot span
As per general rules and guidelines, rafter made of pine wood, for a 20 foot span, size of rafter should be 2″×10″ in which thickness of rafter is 2″ and their depth range is 10 inches. Thus, you need, 2″×10″ rafter placed at 16″ OC are sufficient and better option for you to provide allowable span upto 20 foot for providing great stability for your projects.
Rafter size for 24 foot span
As per general rules and guidelines, rafter made of pine wood, for a 24 foot span, size of rafter should be 2″×12″ in which thickness of rafter is 2″ and their depth range is 12 inches. Thus, you need, 2″×12″ rafter placed at 16″ OC are sufficient and better option for you to provide allowable span upto 24 foot for providing great stability for your projects.
How do i figure out how many Rafters i need
To figure out number of roof rafters you would need, measure the roof length or span between two end of wall in feet. Multiply the roof length in feet by 12 to convert in inches. Then divide it by spacing i.e 24″ or 16″ and add 1 in result to get total number of rafters you needed.
The simple formula to find number of rafters are following: Roof rafters count = ((roof length × 12)/24) + 1. This equation will help you to figure how many rafters you needed. For example, if your roof span is 30 feet long, you will need atleast 16 rafters. i.e (30×12)/24) +1 = 16
How far apart do rafters need to be?, typically, roof rafters need be spaced 24″ apart in the center. But it can be also spaced 12″ or 16″ apart. However, rafters are designed to the individual specification of a particular house. It also depende on local climatic conditions . For example, if you live in a hurricane-prone area, you can move the rafters need to be spaced 16″ in the center.
How many rafters do I need for a 40 ft long roof?
If your roof span is 40 feet long, you will need atleast 21 rafters. Use the formula for rafters count = ((roof length × 12)/24) + 1, and put the span of your roof: rafters count = ((40 × 12)/24) + 1 = (480/24) + 1 = 20 + 1 = 21. Thus, you would require 21 rafters for a 40 foot long roof.
How many rafters do i need for a 10 foot span
If your roof span is a 10 foot long, you will need atleast 6 rafters. Use the formula for rafters count = ((roof length × 12)/24) + 1, and put the span of your roof: rafters count = ((10 × 12)/24) + 1 = (120/24) + 1 = 5 + 1 = 6. Thus, you would need atleast 6 rafters for a 10 foot span.
How many rafters do i need for a 12 foot span
If your roof span is a 12 foot long, you will need atleast 7 rafters. Use the formula for rafters count = ((roof length × 12)/24) + 1, and put the span of your roof: rafters count = ((12 × 12)/24) + 1 = (144/24) + 1 = 6 + 1 = 7. Thus, you would need atleast 7 rafters for a 10 foot span.
How many rafters do i need for a 14 foot span
If your roof span is a 14 foot long, you will need atleast 8 rafters. Use the formula for rafters count = ((roof length × 12)/24) + 1, and put the span of your roof: rafters count = ((14 × 12)/24) + 1 = (168/24) + 1 = 7 + 1 = 8. Thus, you would need atleast 8 rafters for a 14 foot span.
How many rafters do i need for a 15 foot span
If your roof span is a 15 foot long, you will need atleast 9 rafters. Use the formula for rafters count = ((roof length × 12)/24) + 1, and put the span of your roof: rafters count = ((15 × 12)/24) + 1 = (180/24) + 1 = 7.5 + 1 = 8.5, round it as 9. Thus, you would need atleast 9 rafters for a 15 foot span.
How many rafters do i need for a 16 foot span
If your roof span is a 16 foot long, you will need atleast 9 rafters. Use the formula for rafters count = ((roof length × 12)/24) + 1, and put the span of your roof: rafters count = ((16 × 12)/24) + 1 = (192/24) + 1 = 8 + 1 = 9. Thus, you would need atleast 9 rafters for a 16 foot span.
How many rafters do i need for a 18 foot span
If your roof span is a 18 foot long, you will need atleast 10 rafters. Use the formula for rafters count = ((roof length × 12)/24) + 1, and put the span of your roof: rafters count = ((18 × 12)/24) + 1 = (216/24) + 1 = 9 + 1 = 10. Thus, you would need atleast 8 rafters for a 18 foot span.
How many rafters do i need for a 20 foot span
If your roof span is a 20 foot long, you will need atleast 11 rafters. Use the formula for rafters count = ((roof length × 12)/24) + 1, and put the span of your roof: rafters count = ((20 × 12)/24) + 1 = (240/24) + 1 = 10 + 1 = 11. Thus, you would need atleast 11 rafters for a 20 foot span.
How many rafters do i need for a 24 foot span
If your roof span is a 24 foot long, you will need atleast 13 rafters. Use the formula for rafters count = ((roof length × 12)/24) + 1, and put the span of your roof: rafters count = ((24 × 12)/24) + 1 = (288/24) + 1 = 12 + 1 = 13. Thus, you would need atleast 13 rafters for a 24 foot span.
Conclusions:-
As per general rules and guideline, for 10 -12 foot span, generally you need 2″×6″ size of rafter, for 15 -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.
