EN 1991-1-3 (Eurocode 1 Snow Loads)

EN 1991-1-3, Eurocode 1 – Actions on structures – Part 1-3: General actions – Snow loads, is the European Standard for determining snow loads for the structural design of buildings and civil engineering works. It is one of the Eurocodes, the common European structural design standards published by CEN through technical committee CEN/TC 250.

Editions

The first-generation standard was EN 1991-1-3:2003, with a 2009 corrigendum and a 2015 amendment. It replaced the earlier pre-standard ENV 1991-2-3:1995. As part of the second generation of Eurocodes, CEN has published EN 1991-1-3:2025, and its catalogue records withdrawal of the 2003 edition from February 2025. National standards bodies set their own transition timetables, so the first-generation version may remain in use in some countries for a period.

Scope

The standard applies to sites at altitudes below 1,500 m (about 4,900 ft). Snow loads at higher altitudes may be dealt with in National Annexes. It does not cover all special cases, such as impact loads from snow sliding off a higher roof in every situation, or loads in regions with extreme snow conditions without national guidance.

How it works

The design snow load on a roof is calculated from:

• Characteristic ground snow load – taken from national snow maps in each country's National Annex, based on location and altitude.
• Shape coefficients – which convert ground snow to roof snow, depending on roof slope and shape (monopitch, duopitch, multi-span, cylindrical).
• Exposure and thermal coefficients – which allow for wind exposure and heat loss through the roof.

The standard also covers drifting against parapets, higher roofs and obstructions, overhanging snow at eaves, and loads on snow guards.

Relevance to roofing

Roofers and designers use EN 1991-1-3 results to size roof structures, select snow guards, and design for drifts where a low roof meets a taller wall. Drift zones are often where roof failures and leaks occur, because extra load and meltwater build up there.

National Annexes

Each country publishes a National Annex with snow maps and nationally determined parameters. As a result, the same building may have quite different design snow loads in, for example, the UK, Germany or Norway. In North America, the equivalent role is played by ASCE 7 in the US and Part 4 of the National Building Code of Canada.