For flat roofs within the scope of DIN 18531 (unused/used roofs), the mechanical and thermal effects on the roof waterproofing to be expected according to the plan are divided into four action classes, to which the respective waterproofing must be coordinated.
The action classes result from a combination of mechanical (level I: high, level II: moderate) and thermal action (level A: high, level B: moderate). Exposure class IA (high thermal and high mechanical impact) therefore places the highest demands on waterproofing.
Source: bauwion
