The roof pitch angle is a key indicator that distinguishes between a flat, pitched and medium-pitched roof. Knowledge of this parameter is necessary already at the initial stages of cooperation with the architect, when modernizing the existing structure or when choosing a ready-made project. The value of the roof slope has a significant impact on aspects such as the choice of roofing, the selection of roof lighting, the selection of the appropriate roof hatch, insulation materials, as well as the selection of the appropriate roofing team. In this article, we explain how to calculate the roof slope angle and what this parameter means for the investor.
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Table of contents:
What is roof pitch?
The roof slope is simply the slope created by the rafters. Calculating the roof pitch can be done in two ways – either as the angle that the rafter makes with the horizontal, or as the proportion between the height and span of the roof.
Differences in pitch angle between monopitch and duopitch roof
The angle of inclination of a roof, whether monopitch or gabled, is determined by a variety of factors, including the type of roofing material, climatic conditions, as well as aesthetic preferences. A monopitch roof is characterized by a single slope inclined in one direction, which gives it a simple and modern form. A gable roof, on the other hand, consists of two slopes that face opposite directions, creating a more traditional look.
In the case of a monopitch roof, the recommended angle of inclination is in the range of 3 to 45 degrees. This range allows for flexible adaptation to different architectural styles and functional requirements of the building. On the other hand, for a gable roof, the angle of inclination should be between 20 and 45 degrees, which is optimal both aesthetically and functionally, ensuring adequate drainage of water and snow.
Calculating the roof slope angle
There are several methods for calculating the roof slope angle. One of them is to measure the height of the roof in centimeters and convert this measurement into an angle of inclination expressed in degrees or percentages. A useful tool in this process is a table that gives approximate values of the angle of inclination in degrees and percentages for different roof heights. An alternative method is to use the mathematical formula: slope angle = arctg (slope in percentage/100)*180/π, where π is the number pi.
Here you will find out:
e.g. how to determine the angle of 35 degrees
Below is a table showing the relationship between the roof elevation and the angle of inclination, both in degrees and percentages:
| Roof Elevation (in cm) | Tilt Angle (degrees) | Tilt Angle (percentages) |
|---|---|---|
| 25 cm | 14° | 24,9% |
| 30 cm | 17° | 30,6% |
| 40 cm | 22° | 40,4% |
| 45 cm | 24° | 44,5% |
| 49 cm | 26° | 48,8% |
| 59 cm | 28° | 53,2% |
| 75 cm | 37° | 75,4% |
| 84 cm | 40° | 83,9% |
| 90 cm | 42° | 90,0% |
| 100 cm | 45° | 100,0% |
This table is a useful tool for architects, builders and investors to quickly determine the angle of inclination of the roof based on its elevation. The roof elevation values are given in centimeters, and the corresponding angles of inclination are given in degrees and percentages. This makes it easy to adapt the roof design to specific requirements, such as aesthetics, weather resistance or the selection of the right roof system.
Application of the Pythagorean theorem
In general, the roof slope is calculated using the same formula that describes a right triangle. You can use the following equations to find the rafter length and slope:
- rafter² = height² + span² (from the Pythagorean theorem);
- height / span = slope, where the slope is expressed as a percentage;
- Slope = TG (angle), where angle is the slope of the roof in degrees.
Roof slope calculator
Enter both the elevation and span of the roof
What is the minimum roof pitch?
The minimum angle of inclination of the roof is closely related to the type of material used to cover it. For example, when using metal roofing tiles, it is recommended that the angle of inclination of the roof slope is in the range of 10-14 degrees. However, for ceramic and cement tiles, the minimum angle of inclination is usually 10 degrees. In a situation where the roof angle is less than 10-12 degrees, this structure is classified as a flat roof. This is important information for designers and contractors, as the right roof slope is crucial to ensure its durability, effective weather resistance and aesthetic appearance of the building.
What is the minimum roof angle for snow drainage?
The minimum roof angle for snow drainage is about 30°, i.e. an inclination of 6:12 or 7:12. However, this is not the final value, because the roof material, the direction of snowfall and wind are factors that can affect whether snow will slide off the roof. It has been reported that roofs with a slope of even only 10° can evacuate snow. Roofs with a steeper slope will keep less snow out, so if you live in a snow-prone region, a steeper roof slope is desirable.
What is the best roof angle?
The best roof angle depends on the style you want to achieve. If you’re looking for a modern, sleek style, you should use a (not quite) flat roof with a 1:40 pitch.
For the Gothic style, the rafters must be equal to the span (60°), while in the Elizabethan style, the rafters should be longer than the span.
In snowy regions, the roof should have at least a slope of 10/12 (40°) to allow snow to slide down, while the safest roof slope in very windy areas is between 4/12 and 6/12 (18.5°-26.5°).
What is roof pitch multiplier?
The roof pitch multiplier, also known as the roof pitch factor, is a number that, when multiplied by the area covered by the sloped roof, gives the actual area of the roof. Mathematically, it is the square root of ((height/span)² + 1). Roof pitch multipliers are extremely useful when estimating the amount of material needed to cover a new sloping roof, as conventional mathematical methods may not be enough!
Roof angle – does it affect the choice of skylight?
Yes, the minimum roof angle affects the choice of the right skylight. Skylights are adapted to different types of roofs, and their design and installation method depend on the angle of inclination of the roof slope.
- Flat and low slope roofs: For flat roofs or roofs with a very slight slope, flat skylights are usually used. Due to the minimal slope, it is necessary to provide an appropriate structure that will allow water to drain and prevent it from remaining on the surface of the skylight.
- Steeper Slope Roofs: For steeper sloped roofs, such as pitched roofs, skylights are used that are installed in line with the roof slope. Their design must be adapted to the angle of the roof to ensure proper sealing and integration with the roof structure.
The choice of skylight should be made taking into account the angle of the roof to ensure optimal performance, durability and aesthetics. It is worth consulting a professional who will help you choose the right type of skylight for a specific roof. For this purpose, please contact our engineers: https://www.gulajski.pl/swietliki-dachowe/
Roof angle – does it affect the choice of roof access window?
Yes, the minimum angle of inclination of the roof has a significant impact on the choice of roof access window. Roof hatches must be properly adjusted to the angle of the roof to ensure safety, tightness and functionality. See how the angle of inclination affects the choice of the access window:
- Flat and low slope roofs: For flat or slight slope roofs, flat roof hatches are recommended for easy access and do not interfere with the aesthetics of the roof. It is important that the hatch is properly sealed and has a water drainage system to avoid leaks.
- Pitched roofs: With pitched roofs, the access roofs must be adapted to the angle of inclination, which often means the need for more complex access windows that can be integrated into the roof slope. Such hatches ensure safe entry and exit, especially on steeper slopes.
When choosing a roof access window, you should consider not only the angle of inclination, but also other factors such as insulation requirements, weather resistance, and compatibility with the overall roof style and structure. It is recommended to consult an experienced installer or architect to select the most suitable roof access window for your type of roof. For this purpose, please contact our engineers: https://www.gulajski.pl/wylaz_dachowy/
Autor: Tomasz Matuszek; Dział Marketingu - Firma Gulajski