What size Rafter do you need for 10′, 12′, 15′, 16′, 18′, 20′ & 24 foot span, depends on many factors like the type of wood species (S. Pine, Doug. Fir, Hem-fir, SPF and etc), the load they need to support, and local building codes.

Common rafter sizes for those spans are approximately:

1. 10′ span: 2×4 or 2×6

2. 12′ span: 2×6 or 2×8

3. 15′ span: 2×8 or 2×10

4. 16′ span: 2×10 or 2×12

5. 18′ span: 2×12 or larger

6. 20′ span: 2×12 or larger

7. 24′ span: 2×12 or larger

In general, for a 7 to 9-foot span, you can typically use 2×4 rafters, while for a 10 to 12-foot span, you can typically use 2×6 rafters. Likewise, for a 13 to 15-foot span, you can typically use 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, you can typically use 2×12 rafters.

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. How to figure out how many of roof rafters you would need

In general, the roof span is distance between two support end. The roof span may be 10 feet, 12 feet, 14 feet, 16 feet, 18 feet, 20 feet, 24 feet, 27 feet and so on higher.

**Rafter size, definition, span & spacing**

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.

**Common rafter size in roof framing**

The most common size of dimensional lumber used as rafter in roof framing are (inches): 2×6, 2×8, 2×10, 2×12 and 2×14 and as per UK practice, most common size of dimensional lumber for roof rafters measured in millimeter are 100×47, 125×47 and 150×47.

**What size lumber for roof rafters**

The 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. Thickness of rafter should be not less than 2 inches and their depth should be range from 4″ to 14″. 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.

**What size header for 3, 4, 5, 6, 7, 8, 10 and 12 foot span**

**How far can a 2×6 , 2×8 , 2×10 , 2×12 & 2×14 rafter span**

**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.

**Roof rafter spacing**

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.

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.

In general, a 2″×6″ rafter can span up to 10 to 15 foot, while a 2″×8″ rafter can span up to 13 to 19 foot. Moreover, a 2″×10″ rafter can span up to 16 to 23 foot, while a 2″×12″ rafter can span up to 18 to 27 foot. In addition, a 2″×4″ rafter can span up to 7 to 9 foot.

**ALSO READ :-**

**What size Rafter do i need for a 10 foot span**

The rafter size for a 10-foot span need to be 2×6 (measure 2-inches wide by 6-inches deep), which spaced at 24″ OC. So for a span of 10 feet, you need 2×6 size of rafter which spaced at 24″ OC.

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**What size Rafter do i need for a 12 foot span**

The size of rafter for a 12-foot span need to be 2×6 (measure 2-inches wide by 6-inches deep) which spaced at 16″ OC. So for a span of 12 feet, you need 2×6 size of rafter which spaced at 16″ OC.

**What size Rafter do i need for a 15 foot span**

The size of rafter for a 15-foot span need to be 2×8 (measure 2-inches wide by 8-inches deep) which spaced at 16″ OC. So for a span of 15 feet, you need 2×8 size of rafter which spaced at 16″ OC.

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**What size Rafter do i need for a 16 foot span**

The size of rafter for a 16-foot span need be 2×8 (measure 2-inches wide by 8-inches deep) which spaced at 16″ OC. So for a span of 16 feet, you need 2×8 size of rafter which spaced at 16″ OC.

**What size Rafter do i need for a 18 foot span**

The size of rafter for a 18-foot span need be 2×10 (measure 2-inches wide by 10-inches deep) which spaced at 16″ OC. So for a span of 18 feet, you need 2×10 size of rafter which spaced at 16″ OC.

**What size Rafter do i need for a 20 foot span**

The size of rafter for a 20-foot span need to be 2×10 (measure 2-inches wide by 10-inches deep) which spaced at 16″ OC. So for a span of 20 feet, you need 2×10 size of rafter which spaced at 16″ OC.

**What size Rafter do i need for a 24 foot span**

The size of rafter for a 24-foot span need to be 2×12 (measure 2-inches wide by 12-inches deep) which spaced at 16″ OC. So for a span of 24 feet, you need 2×12 size of rafter which spaced at 16″ OC.

**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 and multiply by 2 for both side 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】 2]. 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 at least 32 rafters for both sides. i.e (30×12)/24) +1 = 16 ×2 = 32 rafters.

**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 depends 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 foot long roof?**

In general, for a 40-foot long span roof in a residential building, you need 42 rafters for both sides roof. 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 = 21×2 = 42 rafters. Thus, you may require 21 rafters for a 40 foot roof span.

**How many rafters do i need for a 10 foot span**

If your roof span is a 10 foot long, you will need at least 12 rafters for both side roof. 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 = 6×2 = 12 rafters. Thus, you may need at least 12 rafters for a 10 foot roof span.

**How many rafters do i need for a 12 foot span**

If your roof span is a 12 foot long, you will need at least 14 rafters for both side roof. 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 = 7×2 = 14 rafters. Thus, you may need at least 14 rafters for a 12 foot roof span.

**How many rafters do i need for a 14 foot span**

If your roof span is a 14 foot long, you will need at least 16 rafters for both sides roof. 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 ×2 = 16 rafters. Thus, you may need at least 16 rafters for a 14 foot roof span.

**How many rafters do i need for a 15 foot span**

If your roof span is a 15 foot long, you will need at least 18 rafters for both sides roof. 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 9×2 = 18 rafters. Thus, you would need at least 18 rafters for a 15 foot roof span.

**How many rafters do i need for a 16 foot span**

If your roof span is a 16 foot long, you will need at least 18 rafters for both side roof. 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 = 9×2 = 18 rafters. Thus, you would need at least 18 rafters for a 16 foot roof span.

**How many rafters do i need for a 18 foot span**

If your roof span is a 18 foot long, you will need at least 20 rafters for both sides roof. 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 = 10×2= 20. Thus, you would need at least 20 rafters for a 18 foot roof span.

**How many rafters do i need for a 20 foot span**

If your roof span is a 20 foot long, you will need at least 22 rafters for both sides roof. 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 = 11×2 = 22 rafters. Thus, you would need at least 22 rafters for a 20 foot roof span.

**How many rafters do i need for a 24 foot span**

If your roof span is a 24 foot long, you will need at least 26 rafters for both sides roof. 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 = 13×2 = 26 rafters. Thus, you would need at least 26 rafters for a 24 foot roof span.

**Conclusions**:-

In general, the size of rafter for a 10 to 12-foot span ought to be 2×6, whereas the size of rafter for a 15 to 16-foot span ought to be 2×8. Moreover, the size of rafter for a 18 to 20-foot span ought to be 2×10, whereas the size of rafter for a 20 to 27-foot span ought to be 2×12. In addition, the size of rafter for a 7 to 9-foot span ought to be 2×4.