TS EN 13859-2

TS EN 13859-2 is a standard in the family of flexible waterproofing sheets, focused on the definition and basic characteristics of underlays used as underlays for walls. The topic is not waterproofing in the abstract, but the functional layer placed behind external wall claddings to help manage rainwater, wind-driven moisture and related exposure in the building envelope.

The technical role of a wall underlay

In general technical terms, wall underlays are an intermediate functional layer between the outer cladding and the supporting substrate. Their purpose is to reduce the chance of water reaching the wall assembly, support controlled drainage, and in some systems contribute to air tightness and moisture management. The flexible-sheet format makes it easier to install the product in rolls and to adapt it to junctions and wall details. For these products, material selection, laps and joints, mechanical resistance, and behaviour under environmental exposure are key factors in overall system performance.

How this standard family should be read

As the title indicates, this document addresses underlays for walls. Although it belongs to the same broad product family as roof underlays, the position in the building envelope and the exposure conditions are different. That means the general principles of flexible waterproofing sheets still apply, but wall-specific detailing, interfaces and surface behaviour need separate consideration. For buyers and specifiers, this identifies the document as a terminology-and-characteristics standard for wall underlay products rather than a generic waterproofing rulebook.