What Are Snow Load Zones?
Germany is divided into five snow load zones: Zone 1, Zone 1a, Zone 2, Zone 2a and Zone 3. The classification is based on long-term snow measurements and indicates how much snow load per square meter of ground area can be expected in a given region.
The zones are defined in DIN EN 1991-1-3 with the National Annex (NA). Every building site in Germany is assigned to a zone. Assignment follows administrative boundaries (districts and independent cities).
Which Zone Applies Where?
Zone 1 covers large parts of northern Germany: the coasts, the North German Plain, the Rhine Valley, and parts of the Rhine-Main area. Snow is infrequent here and rarely persists for long.
Zone 1a covers transitional areas between lowlands and central mountain ranges, such as parts of Lower Saxony, North Rhine-Westphalia and Hesse.
Zone 2 covers the central mountain regions: Harz, Thuringian Forest, Ore Mountains, Black Forest (lower elevations), Rhoen and parts of the Swabian Alps.
Zone 2a covers higher elevations of the central mountains and the northern Alpine foothills.
Zone 3 covers the highest snow load areas: southern Alpine foothills, Alpine edge, and Bavarian Alps. Extreme snow volumes can occur here.
The Calculation Formulas
The characteristic ground snow load (sk) is calculated for each zone using a specific formula that accounts for terrain elevation (h in meters above sea level):
Zone 1: sk = 0.19 + 0.91 x ((h + 140) / 760)^2
Zone 1a: sk = 0.25 + 1.91 x ((h + 140) / 760)^2
Zone 2: sk = 0.25 + 1.06 x ((h + 140) / 760)^2
Zone 2a: sk = 0.25 + 1.61 x ((h + 140) / 760)^2
Zone 3: sk = 0.31 + 2.91 x ((h + 140) / 760)^2
Example Calculations
Munich (Zone 2, approx. 520 m elevation): sk = 0.25 + 1.06 x ((520 + 140) / 760)^2 = 0.25 + 1.06 x 0.868^2 = 0.25 + 1.06 x 0.753 = 1.05 kN/sqm.
Hamburg (Zone 1, approx. 10 m elevation): sk = 0.19 + 0.91 x ((10 + 140) / 760)^2 = 0.19 + 0.91 x 0.197^2 = 0.19 + 0.91 x 0.039 = 0.225 kN/sqm.
Garmisch-Partenkirchen (Zone 3, approx. 710 m elevation): sk = 0.31 + 2.91 x ((710 + 140) / 760)^2 = 0.31 + 2.91 x 1.118^2 = 0.31 + 2.91 x 1.250 = 3.94 kN/sqm.
From Ground to Roof: Shape Coefficient mu
Ground snow load is not identical to the load on the roof. The shape coefficient mu accounts for the fact that snow partially slides off pitched roofs:
At 0 to 30 degrees roof pitch: mu = 0.8 (80% of ground load). At 30 to 60 degrees: mu = 0.8 x (60 - alpha) / 30. Above 60 degrees: mu = 0 (snow slides off completely).
For a gable roof at 40 degrees in Munich: mu = 0.8 x (60 - 40) / 30 = 0.533. Snow load on roof: s = 0.533 x 1.05 = 0.56 kN/sqm.
Practical Meaning of the Values
1 kN/sqm equals approximately 100 kg per square meter. A snow load of 0.56 kN/sqm means 56 kg/sqm on the roof. For a roof area of 170 sqm, that totals 9.5 tonnes of snow.
These loads must be considered in the structural calculation of the roof frame. The structural engineer sizes the cross-sections of rafters, purlins and posts to safely carry the snow load (together with self-weight and wind load).
In snowy regions, it may be advisable to build steeper roofs (above 45 degrees) so that snow slides off. However, snow guard systems must then be installed to prevent snow from falling uncontrolled onto walkways and driveways.