TS EN 13859-2

TS EN 13859-2 is a waterproofing-related standard for flexible sheets used as underlays in wall applications behind external wall coverings. These products are installed in the layer behind the cladding to reduce the penetration of wind and water from the outside, so their role is to provide a secondary protective function within the building envelope.

The function of wall underlays

In general technical terms, wall underlays sit behind the outer cladding and help manage moisture that reaches the outer layers of the wall. The term “underlay” here does not describe the visible finish, but a functional layer that supports the overall weather resistance of the wall build-up. That distinction matters because the cladding, the underlay and the supporting wall each contribute differently to water management, air control and the long-term performance of the envelope.

What this standard covers

The focus of this document is the characteristics of flexible sheets intended for use as wall underlays behind outside wall coverings. In other words, it addresses the product type and its application context, not the full set of test procedures or numeric performance thresholds on its own. In practice, such products are associated with properties such as water resistance, vapour transmission behaviour, mechanical strength and resistance to stresses encountered during installation and service.

• Defines a protective underlay layer used behind external wall cladding.
• Addresses products intended to limit wind and water ingress from the outside.
• Applies to flexible-sheet materials used in wall constructions.
• Highlights the functional role of the layer within the building envelope.