A roof having 4 inches of rise for every 12 inches of run has 4 in 12 roof pitch. That means such a roof has a slope of 4:12 and it translates to degrees as about 18.4 degrees.
Any roof with pitch is not too steep you might be able to walk on such a roof.
4:12 roof pitch (18.43 degrees) is less steep than 6:12 roof pitch (26.57 degrees). Pitch is always expressed as inches per feet. That means to express as “X in Y” the Y will always be 12 or 1 feet while X can vary from 1 to 12 (1 being lowest while 12 being highest).
12:12 roof pitch will make 45 degrees and that is too steep for a roof. Some common roof pitches are 4 in 12, 6 in 12, 8 in 12, and 10 in 12.
Table of Contents
- What is pitch of a roof?
- Types of pitches
- How pitch of roof is expressed?
- 4 on 12 roof pitch
- 4 on 12 roof pitch calculator
- Procedure for calculating the angle of roof
What is pitch of a roof?
Pitch is an inclination of the roof, and it is defined as the fraction obtained by dividing the total rise of roof from horizontal plane by the span of a building.
Here span is a horizontal distance between the outside of one wall top plate to another. The design of pitch of roof plays a very important role for the right construction of a house.
In earlier time houses were made of timber and the roofs were pitched roofs. Even today timber is used for building light construction homes in hilly areas and cold climatic regions.
Also Read: What Is the Standard Roof Pitch?
Types of pitches
There are different types of roofs which can be constructed. It may be flat roof with very few degrees slope or it can be pitched roof /sloping roof.
The choice of type of roof depends upon the many factors which includes the loading conditions, type of material used, type of building and climate of the region.
The areas which face heavy rainfall and severely affected by climatic conditions it is recommended to construct pitched roof to ensure adequate drainage of rainwater and removal of snowfall.
Also Read: How to Plan for a Roof Remodeling Project
How pitch of roof is expressed?
The pitch of roof can be expressed in different ways it can be ratio, fraction or degrees.
There is no single standard to measure the pitch of roof it depends upon some factors which include the type of material, intensity of rainfall and location of building.
- For normal rainfall areas flat roof is constructed with slope of 10 degree.
- Similarly in moderate to high rainfall areas pitched roofs with slope of 15 to 20 degrees is constructed.
- For very high rainfall areas pitched roofs with slope of 20 to 30 degrees is recommended.
4 on 12 roof pitch
The 4 in 12 pitch is the most common roof slope used in construction of roofs. Here 4 in 12 means for every 12 units horizontal distance there is a rise of 4 units. It is a ratio of two same units, so its final parameter is unitless. This pitch can also be expressed in other ways such as 1 in 3 or 18.43 degrees.
This slope is moderate and enough to remove water quickly and also comfortable to walk on it. It is preferred in areas where rainfall and climatic affects are not very severe.
In gable type pitched roof there is a ridge at the middle of span with slope on both sides in opposite direction. This type of roof is constructed by providing sloping rafter from ridge board to eaves in both the directions of ridge.
The pitch of roof 4 in 12 is normally used.
Here 4 in 12 means that rafter will rise 4 units for 12 horizontal units.
For example, if we have a 20 ft span of house then ridge board will be provided at 10ft horizontal distance and vertical height will be according to the slope of roof .if recommended slope is 4 in 12 then it means that for every 1 ft horizontal distance a rise of 4 inch will be provided or we can also say that a total of 39.5 inch rise of rafter will be provided for 10 ft horizontal distance exactly at the middle of span
4 on 12 roof pitch calculator
The pitch of any roof is very easy to calculate.
It can be calculated by the simple mathematical trigonometric calculation. The concept is simple which is rise/run method.
Here rise is representing the y value which is in vertical direction and run is representing the x value in horizontal direction.
Slope ratio = Rise/Run
Slope ratio = y/x
The slope percentage and slope angle is also sometimes used to represent the slope or pitch of roof which can be calculated by the formulas given below
Slope ratio = (Rise/Run) ×100
Slope angle = tan^-1(Rise/Run)
Roof pitch (x:12):
Roof pitch (%):
Roof pitch (degrees):
Procedure for calculating the angle of roof
The first step is to calculate the vertical rise of rafter and horizontal distance up to middle of span exactly below the ridge.
The second step is to divide the vertical rise by horizontal distance value which will give a pitch of 4 in 12 for this case.
Then find the inverse tangent of 4 in 12 to get the angle in degrees
Roof slope angle = 18.43°
This simple mathematical procedure can be used to calculate the pitch and angle of any pitched roof and any other sloping member.
The pitch of roof is an important factor which depends upon the many factors such as climate and material of building. The pitch of roof can be expressed by different ways it can be a slope ratio, slope percentage or roof slope angle.
The roof angle of any roof can be calculated by using simple trigonometric method. The roof pitch 4 in 12 can be written as 4/12 or 1/3. It means that a rise of 4 units will be provided for every 12 horizontal units.
The 4 in 12 pitch is equal to 18.43 degrees angle of roof slope. This pitch is best for many residential houses in cold and wet weather climatic regions.