Calculate a pitched roof

Even on existing roofs must be worked again and again. Be it the replacement of rafters and purlins, or even the re-roofing of the roof. If a roof is to be covered in the same way as before, only the roof area needs to be calculated. However, if another material is used, it gets more complicated. But for all calculations there are formulas.

The saddle roof - a geometric figure

The calculations on the roof are to be found in geometry, after all, a roof is a geometric shape. Depending on what you want to calculate, you need different information. For this it is first important to know the individual terms.

  • First (top point where the rafters converge)
  • Eaves (the lowest, outermost roof point or drip edge)
  • Roof overhang (the measure from facade to eaves)
  • Verge, roof overhang (the overhang at the ridges)
  • Rafter and purlin length
  • Roof pitch angle
  • Length and width of the roof
  • Length and width of the outer walls

Using the appropriate geometric formulas, all calculations can be made on the saddle roof with these dimensions. However, the saddle roof can be added to a special feature.

Calculate a pitched roof: roof

The saddle or gabled roof in its variety of designs

The pitched roof is probably the most widespread roof in Central Europe. It is formed by two roof surfaces that converge longitudinally in the middle and drop off at an individual angle. At the longitudinal ends, the roof on the facade is completed.

Roof pitch at saddle roof

Depending on the design of the gable roof, this gable roof construction also receives more specific designations. In addition, a distinction between a symmetrical and an asymmetrical pitched roof.

  • Roof pitch smaller or maximum 30 degrees: flat gable roof
  • Roof pitch of 62 degrees: Old German or gothic roof
  • Roof pitch 45 degrees Angle or north German roof
  • in the transverse view, an equilateral triangle (verge as a leg): Old French or Old Franconian roof


The variety of asymmetric gable roofs is great. The eaves heights can be different. Similarly, the roof pitch angle can vary from one to the other half of the roof - at the same height as well as different eaves heights and different long verges.

Other important calculations

Depending on how the pitched roof is to be executed, for example, cement or brick pans as a roofing, the load capacity of the roof must be calculated. Here, too, you should include different aspects, some of them compulsory, some of them voluntary and according to your personal planning needs.

  • possible snow load
  • possible wind load
  • used materials for roofing
  • possible preparation for photovoltaic (electricity) or solar thermal (hot water)

Snow and wind load

Every region of Germany is different. In the north of Germany large amounts of snow are unlikely, but strong winds occur. However, in very cold and snowy areas like the Allgäu there can be several meters of snow load. In windy areas, the steepest possible roof seems like a sail, while on a steep roof in a snowy region not so much of it can remain on the roof.

These considerations need not only be taken into account in individual considerations, depending on the region maximum or minimum pitch angles are required.

Used roofing, photovoltaic and solar thermal

The strengths of rafters, purlins and buttresses are also crucial in terms of the load-bearing capacity of the house. Especially in the 1980s and even in the 1990s, numerous houses were built in which solar systems were not considered. After 2000, there was massive funding, but many roofs were not designed for it.

Calculations by the handyman or the structural engineer

You can do some of the rooftop calculations completely on your own - for example, a simple area calculation if you want to rebuild your roof with roof tiles of the same age as the old pans. However, many calculations require a sound knowledge of structural design.

Although this allows you to roughly calculate the roof yourself, the final decisive calculation is carried out by the structural engineer or architect, because in the case of many modifications and alterations, the building plan must also be signed and approved by the Office.

Tips & Tricks

First carry out calculations yourself and then present your results to your structural engineer. It may save time and only need to verify your calculations once more. And saved time means saved money.

Video Board: Roof Pitch and How-to Manipulate rise over run