Roof Slope: typical, minimum

Proper selection of material and calculation of roof slope are very important aspects of the preparatory work for the construction of the roof.

Roof slope is very responsible action. Reliability of the design and resistance to various loads depend on the correct choice of roof slope.

The influence of different conditions

Various conditions can influence the angle of the roof slope. It is important to consider following conditions:

  • Material of the roof;
  • Climatic conditions;
  • Draft design of the roof;
  • Façade of the building;
  • Purpose of the structure.

Thus it is better to install roof with minimum slope in regions where strong winds blow. Also it is recommended to construct roofs with large angles of inclination in areas, where heavy rainfalls are dominated.

So if you want to calculate the angle of slope, you should take into account all described circumstances. Also the calculation of roof slope must be based on the range of 9-60 degrees. Usually, the optimal value lies within between 20 and 45 degrees.

In such cases, you can use almost any type of roofing material, such as decking, metal tile, slate and many others. Although these materials have some special requirements.

In addition, you have to pay attention to the appointment of the attic. Thus, if the attic will not be used as a dwelling, you don’t need to make high slope of the roof. But if you want to realize some interesting room design ideas your roof must have sufficient slope angle.

Video: Home Inspection Training Class: “Inspecting Roof Slope and Pitch”

You can use different design ideas for homes with high lofts. There are a lot of bedroom ideas (for example, it can be design in kerala style) in this case, also you can accommodate a big wardrobe and external walking surface on your attic.

Kerala design of slope roof
Kerala design of slope roof

Moreover with the use of large windows you can make visual extension of the room area. Also with this you will be able to improve the lightning of the attic.


It is really important to consider materials, which you plan to use to cover the building. Decking is one of the most popular types of roofing. Minimum roof slope in this case can be more than 12 degrees, because it has relatively light weight.

Rolled roofing (polymer, ruberoid and membrane roof) is related to low slope roofing materials. This definition means that it is not recommended to install these materials on the roof with large angle.

In general, in this case angle of slope may reach about 2-5 degrees. The exact value depends on the number of layers, which you will use during the installation.

It is important to find the optimal balance for shingles installation. Because you should achieve such angle of slope, which will allow you to ensure the correct and fast moisture removal from roof. And on the other hand, roof slope must be not too large, so it will not be destroyed by strong wind or snowfall.

In practice, minimum angle of the roof slope reaches about 20 degrees. But this value can be changed due to the depending on the availability of additional strengthening structures and the reliability of crates.

In some cases you can use additional reinforcement details to improve the strength of roof, where the angle is too high. Also if construction has big area it is important to ensure the availability of additional gutters and drains on the roof.

Dependence of the roof slope from material
Dependence of the roof slope from material

You should pay great attention to the improvement of insulation of the construction with roof slope. You should remember that the bigger will be the insulation, the more reliable will be the structure.

For the additional water resistance you can cover the underlayment of roof coating with cement or other roofing product, which has hermetic features.

Also special attention should be paid to the roofing ventilation system. Vents must be properly seamed and reinforced, because they are the most vulnerable places of roof with slope.

During the installation process it is important to use special tool, which will help you to hold the correct slope angle of the roof. For example, it can be roof pitch gauge.

You can use smartphone application as a pitch gauge
You can use smartphone application as a pitch gauge


So let’s look on the computation process in details. Also you should use special mathematical formulas and diagram to make your task easier. For example, table of degrees and percentage ratio of the roof slope can be really useful in calculations.

Roof slope factor
Roof slope factor

Thus roof slope can be calculated through the elevation of the ridge. For this purpose you should determine the ration between the ridge height and half of pledging.

Then this result should be multiplied on 100. Then in accordance with this percentage, using the table you can determine the roof slope, which will be expressed in degrees.

Roof pitch factor
Roof pitch factor


It is important to consider all loads, which act on the construction to make correct calculation of typical roof slope. So you should pay attention to the following circumstances:

  • Total mass of the construction;
  • Snow load for a specific region.
Roof slope chart
Roof slope chart


At first, you should determine the weight of one square foot of each layer of the roofing pie. Result should be added together. After that the result must be multiplied on 1.1 (special multiplier).

During the calculations it is recommended to use following mathematical data:

  • Length of rafters;
  • Tangent for the angle of inclination;
  • Half of the width of home;
  • Height of the ridge.

Except of the mathematical formulas you can also use the Bradis table for the comfortable conversion of angles. In addition you should use such formulas:

For the determination of length of rafters – A x B = C,

where   A – height of ridge;

B – angle between line of the pitch and slope. This numeric value must be expressed in degrees.

Also you can read some useful guidelines to learn more about the calculation of the roof slope. It is recommended to make detailed estimates and calculations for houses or garage plans in each case before the start of installation.

In conclusion, it is need to say that it is not so easy to perform correct calculations of the roof slope by yourself. However, it is quite possible to cope with this process after reading some tips and guides about it.

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