In Germany, where rain is a frequent and serious problem, ZVDH (Zentralverband des Deutschen Dachdeckerhandwerks – German Association of Roofers) has established the following categories for under-tile membranes:

Unterdachbahn (under-roof membrane): impermeable membrane that must guarantee impermeability in any situation, even when the roof is not able to guarantee impermeability to heavy rain (e.g. due to lack of slope or particular roof shapes). Can be used up to a minimum slope of 5° (8.7%). In this category the best products are those which are heat welded at the overlaps for greater reliability. Under-roof membranes are also classified into:

Wasserdicht (impermeable), the membrane is installed over the ventilation counter batten so that the batten hole is always at the highest point.

Regensicher (rain resistant), the membrane is positioned underneath the ventilation counter batten and sealed using nail sealing tape

Unterdeckbahn (under-roof protective membrane): impermeable membrane installed on rigid structures (e.g. wooden planks or concrete screed) or flexible structures (e.g. insulating panels) and must guarantee impermeability only in the event of leakage from the roof. Can be used up to a minimum slope of 10° (17.7%) only with all the joints sealed and the use of nail sealing tape.

Unterspannbahn (under roof covering membrane): impermeable membrane that can also be installed directly cantilevered on the roof’s supporting beams, in tensed or untensed position and must guarantee impermeability only in the event of leakage from the roof.

Vapour breathability – Water vapour

Air is a gas mixture of nitrogen (78%), oxygen (21%) and other gases such as carbon dioxide, water vapour (1%). Humans cannot detect water vapour easily and it is only detected in certain situations such as when it meets a cold surface (a window for example) when it turns into condensation. Water vapour is produced in the home as we go about our daily activities (washing, having a bath, cooking, etc.). Cooking produces approximately 600 – 1500 g/h of water vapour, having a bath produces about 700 g/h and taking a shower produces around 2600 g/h.

Adding up the total amount of water vapour that each person produces in the home (in an average family of 2 adults and 2 children) the figure amounts to approximately 12-15 litres of water a day. This enormous amount of humidity highlights the importance of insulating our homes properly and using our homes in the correct way. The amount of humidity in a home is only partially absorbed by the air and any excess humidity, unless it is removed by correctly ventilating the rooms, collects on room surfaces; when it meets cold surfaces it can be damaging to health as it worsens the air quality of the rooms, causing wall coverings to peel away from the walls, wooden floors to lift and stains and mildew patches to form on the walls.

TOP SK version created by Riwega experts

To guarantee a perfect seal against water, air and wind we recommend installing the TOP SK version of our breathable layers and membranes. This version has a dual integrated acrylic tape. This system makes it possible to achieve a roof that is impermeable to water, air and wind and is breathable at the same time. When laying this version, it is sufficient to fit the upper and lower overlaps of the breathable layers and membranes and then remove the protective film, sticking the two tapes together to form a perfect and long-lasting bond between the two layers. This method of bonding ensures impermeability to water on slopes of 10 degrees or more.