CalcDachneigung Calculator – Roof Pitch & DIN 18531 Check
Last updated: 2026-09-28
How to Use This Dachneigung Calculator
This calculator helps roofers, architects, and DIY enthusiasts quickly determine the pitch of a roof from basic measurements. You only need two values: the vertical rise (the height difference between the lowest and highest points of the roof surface) and the horizontal run (the flat distance over which that rise occurs). Once you enter these, the tool computes the angle in degrees, the slope as a percentage, and a simplified pitch ratio (like 1:2). It also checks whether the pitch meets the minimum requirements of German DIN 18531 for your chosen roof covering – Ziegel (clay tiles), Schiefer (slate), or Bitumen. This is especially useful when planning a new roof or verifying an existing one for compliance.
Formula and Methodology
The core calculation uses trigonometry: the roof pitch angle is the arctangent of rise divided by run. Specifically, angle in degrees = atan(rise/run) × (180/π). The slope in percent is simply (rise/run) × 100. For the pitch ratio, we reduce the rise and run to the smallest integer ratio, e.g., rise 2.5 m and run 5 m becomes 1:2. The DIN 18531 check uses the following minimum angles: Ziegel 22°, Schiefer 25°, Bitumen 5°. These values are based on standard requirements for waterproofing and are widely accepted in Germany. If your calculated angle is equal to or greater than the minimum for the selected covering, the roof is considered compliant under normal conditions.
Practical Examples
Example 1: Rise = 2 m, Run = 5 m. Angle = atan(2/5) = 21.8°. Slope = 40%. Pitch ratio = 1:2.5. For Ziegel (min. 22°), this is just below the minimum, so it would not comply without additional measures. For Bitumen, it easily passes. For Schiefer, it fails.
Example 2: Rise = 3 m, Run = 4 m. Angle = atan(0.75) ≈ 36.87°. Slope = 75%. Pitch ratio = 3:4. This passes for all three coverings.
Example 3: Rise = 0.2 m, Run = 10 m. Angle = atan(0.02) ≈ 1.15°. Slope = 2%. This is only suitable for Bitumen with special waterproofing, as it is below the standard 5° minimum.
Tips and Best Practices
Always measure rise and run accurately using a level and tape measure. For existing roofs, you can measure the rise over a known horizontal distance. Remember that DIN 18531 minimums are baseline requirements; local building codes, snow loads, wind zones, and manufacturer instructions may impose stricter limits. When in doubt, consult a structural engineer or roofing professional. Also note that the type of underlayment and the method of fixing can allow lower pitches than the standard minimums, but this requires careful design. Use this calculator as a quick check, not as a substitute for professional advice.
FAQ
What is the minimum roof pitch for Ziegel (clay tiles) according to DIN 18531?
DIN 18531 generally requires a minimum roof pitch of 22° for Ziegel (clay tiles) when using standard underlayment. However, for pitches below 22°, special measures such as additional underlayment or sealed sub-roof may be allowed. Always check the manufacturer's instructions and local building codes.
How do I convert roof pitch from degrees to percent?
Use the formula: slope_percent = tan(angle_deg) × 100. For example, a 45° roof has a slope of 100%. Our calculator does this conversion automatically when you enter rise and run.
What is the minimum pitch for Bitumen (bituminous roofing) under DIN 18531?
For Bitumen roofing, DIN 18531 typically requires a minimum pitch of 5° (about 8.7% slope). However, for pitches below 5°, special waterproofing systems are required. Always consult a roofing professional.
Can I use this calculator for flat roofs?
Yes. For flat roofs, enter a small rise and a large run. The calculator will show the angle and slope, and flag whether it meets DIN 18531 for the selected covering. Note that flat roofs often have additional requirements beyond pitch.