To calculate the rafter length for a 3/12 roof pitch, you can use the Pythagorean theorem. The 3/12 pitch means that for every 12 units of horizontal run, there is 3 units of vertical rise.

What is a 3/12 roof pitch? A 3/12 roof pitch means that for every 12 inches (or 1 feet) of horizontal run, the roof rises 3 inches in vertical height. It’s a way of expressing the steepness or slope of a roof.

Here’s the formula to calculate the rafter length (hypotenuse): Rafter Length = Square Root of (Run^2 + Rise^2).

Pitched Roop is very much popular in United States, United Kingdom, other European countries and imperial state. Everybody need a new house with a classical appearance, roof is the one of the most important part of any building structure that prevents the other structure of building and inhabitant from adverse climatic weather condition and also ensure the privacy for the inhabitants. In earlier time from the beginning of civilization peoples are always looking for or house which built by timber covered with roof to prevent from heavy rainfall and snowfall conditions.

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. These are two types of roof structure based on slop.

Flat roof is type of roof in which slope is generally less than 10°, which only enable to ensure adequate drainage of rainwater in low to moderate rainfall regions. Pitched roof is type of roof comprising sloping surface or surface with an angle of usually over 20°, generally it slopes downward in one two or more parts depending on design and construction.

In this article you know about 3/12 roof pitch rafter length and how long is a 3/12 pitch roof and how to calculate length of roof rafters for 3/12 pitch of roof. Before calculating length of roof rafter for 3/12 roof pitch you know some points related to this one.

Roof Rafter:- 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. Length of roof rafters 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.

The first step for deciding to figure out length of roof rafters in conventional roof framing is to layout and cut a common rafter pattern. The length of rise and run of the common rafter will determine the height of the ridge board as well as the length of any hip / valley rafters that may be involved with a conventionally framed roof. Conventional framing of roof rafters falls under the heading of rough framing carpentry. Anyone who has ever tried framing a roof can tell you it is a fine tuned skill that can only be acquired with experience.

**Rafters of roof definition**:- distance between the top ridge on roof or hip of the roof to the wall plate of external wall.

**Span of roof** :- span of roof is the clear distance between the two supporting arc,beam, external brick wall or beam truss.

**Run of roof** :- in rafter roof framing Run of roof is horizontal distance from external wall outside plate to the point which are directly below centre of Ridge. In general term run of root is half of span of roof. Run of roof = span of roof/2.

**Rise of roof** :- it is vertical distance between top of ridge to the centre of clear span between two support.

**Pitch of roof** :- it is the inclined angle formed between Rafters of roof and run of roof. Which of roof is calculated by number of inches it Rises vertically for every 12 inches in extend horizontally. for example a roof that Rises 3 inches vertically for every 12 inches of horizontal run. So pitch of roof is equal to = rise/run = 3/12.

Rise is define as vertical change in height per unit of horizontal length or run. For example a pitch of 3/12 represents 3″ vertical height or rise for every 1 foot or 12 inches of horizontal distance or run.

Run is defined as the distance from the outside of wall top plate to a point directly below the centre of the Ridge or hip. It is a horizontal distance for pitch and Rafter is a structural component used as part of roof construction that it runs from the ridge of roof or hip of roof to the wall plate of external wall.

**Rafter length table 3/12 pitch**

In general, at 3/12 pitch, for the 30 feet wide building, the rafter length need to be 15.46 feet, while for the 28 feet wide building, the rafter length need to be 14.43 feet. Likewise, for the 24 feet wide building, the rafter length need to be 12.37 feet, while for the 20 feet wide building, the rafter length need to be 10.31 feet. In addition, for the 16 feet wide building, the rafter length need to be 8.25 feet.

Here is the roof rafter length table 3/12 pitch for a 16 foot, 20 foot, 24 foot, 28 foot and 30 foot wide building.

**3/12 roof pitch rafter length | How long is a 3/12 pitch roof**

Pitch for roof or slope means you how many inches the roof vertical rises for every 12 inches or 1 foot in horizontal distance run. An Example of a pitch for roof would be a 3/12 or “3 in 12” slope means that the roof vertical rises 3 inch for every 1 foot or 12 inches of horizontal distance run.

Regarding this **“how to calculate rafter length for 3/12 roof pitch?”,** generally 3/12 roof pitch rafter length is calculated from the Pythagoras theorem of right angle formula in which hypotenuse of right angle triangle is length of rafter, their height is rise and base is run and you can use following formula and equation to calculate the length of rafter.

● Rafter^2 = rise^2 + run^2 (by Pythagoras theorem of right angle formula)

● Pitch = rise/run (where pitch in express in percentage

● Pitch = tan (angle), where angle is pitch of roof expressed in degree.

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Here you have given roof pitch = 3/12 and span of about 30 feet, then run = span/2, hence run = 30/2 = 15 feet, you know pitch = rise/run, so 3/12 or 1/4 = rise/run, hence rise = run/4, putting the value of run you get rise = 15/4 = 3.75 feet.

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**3/12 roof pitch rafter length | How long is a 3/12 pitch roof**

Calculate the roof rafter length for 3/12 pitch, as Rafter^2 = rise^2 + run^2, Rafter^2 = 3.75^2 + 15^2, Rafter^2 = 14+225, rafter = √239, Rafter = 15.46 feet or 4.712 meters, hence rafter length for 3/12 pitch roof will be 15.46 feet long.

The rafter length for a 3/12 or “3 in 12” roof pitch is approximately 15.46 feet or 4.712m long for 30 feet span. It will goes up when span is increases or will goes down if span is decreases. Note that this is not the actual length of the roof rafter. If you plan to have overhang, etc. the rafter member will be longer.