EN 12326

EN 12326 is the European Standard for natural slate used in roofing and cladding. Part 1, Slate and stone for discontinuous roofing and external cladding – Specifications for slate and carbonate slate, sets the product requirements. Test methods were historically published as a separate Part 2. The current edition of Part 1 is EN 12326-1:2014, which replaced the 2004 edition; CEN completed a periodic review of it in 2025.

Scope

EN 12326-1 covers slate and carbonate slate (slate with a significant carbonate content) for discontinuous roofing, where individual slates overlap, and for external cladding. It excludes other stones and man-made products such as fibre-cement, concrete, polymer, metal and clay "slates." It also does not deal with appearance, internal use, bonded cladding or installation rules.

What it measures

The standard sets out properties that a slate producer must test and declare, including:

• dimensions, thickness and flatness tolerances
• water absorption
• resistance to freeze-thaw cycles
• thermal cycling, which can reveal unstable minerals such as iron sulfides (pyrite) that may rust and stain or break down
• carbonate content and resistance to sulfur dioxide exposure, which affects durability in polluted air
• flexural strength, used to calculate minimum thickness

Results are expressed using codes (for example for thermal cycling and water absorption) so that buyers can compare slates from different quarries. Because natural slate varies, quality depends on the specific quarry and seam.

Market context

Spain is the world's largest producer and exporter of natural slate and supplies most of Europe's roofing slate; Brazil is the second-largest producer. Imported slates from outside Europe are also sold against EN 12326. Well-fixed slate roofs typically last many decades, and good slate can last far longer.

Related standards

• In North America the equivalent is ASTM C406, which grades slate S1 to S3.
• UK installation practice is in BS 5534; in France, slate roofing is governed by the DTU 40 series; in Germany, by the ZVDH rules.