Zero-threshold entrances—that is, level transitions at exterior doors—are a fundamental requirement for accessible construction. This is becoming increasingly important in light of demographic change. According to a 2021 estimate by the Federal Statistical Office, the number of people of retirement age will increase by 22% by 2035. Zero-threshold doors—including those leading out to a balcony or patio—ensure that people with physical limitations can move about freely without assistance and enjoy a high quality of life. However, when creating zero-threshold access to outdoor areas, structural challenges arise, particularly regarding effective waterproofing.

The fact that only a zero-threshold design constitutes an accessible threshold is stipulated in DIN 18040, “Standard for Accessible Construction.” This standard applies to all new buildings and also serves as a guideline for renovations and modernizations. The standard now interprets accessibility more strictly than it did a few years ago. While door thresholds with a lower edge of less than 2 cm were initially declared accessible, the German Institute for Standardization (DIN) e. V. declared this interpretation inadmissible in 2013. Since then, the standard states:

A zero threshold, which was previously considered a special solution, is now required as the standard—including for barrier-free access to balconies or patios. To prevent moisture from entering, reliable drainage and a secure connection to the building structure are essential.

To find a suitable waterproofing solution for windows or doors with a zero-threshold opening to the exterior, there are many factors to consider: What is the wall construction like—for example, is there a composite thermal insulation system in place? What type of window is it (tilt-and-turn unit, sliding door, etc.)? And most importantly: What are the substrate conditions? Ultimately, a solution is needed that is tailored to the specific application. One system that has proven effective on a variety of substrates is Triflex ProDetail. This liquid waterproofing system, based on polymethyl methacrylate (PMMA for short), features a special elastic nonwoven insert, allowing the material to conform tightly—like a second skin—even around complex geometries. Its reliability has been confirmed by the Institute for Window Technology (ift Rosenheim).

In cooperation with ift Rosenheim, we at Triflex have developed an innovative leak test for waterproofing systems between the zero-threshold, the profile, and the reveal. Based on DIN EN 1027 (standard for driving rain resistance of windows and doors), the area between the exterior door and the threshold was subjected to water pressure of up to 600 pascals. The water and pressure were applied directly to the waterproofing. The result: Even under these conditions, the waterproofing provided an effective barrier against moisture. Triflex ProDetail achieves the highest class for driving rain resistance (Class 9A based on DIN EN 12208). Initial internal tests even demonstrate performance in extra classes up to E1200. In the latter case, a water pressure of 1,200 pascals—twice that of Class 9A—is applied to the waterproofing. The use of the PMMA-fabric-reinforced system—for example, in combination with a floor-level installation profile—is therefore also approved—as the first and only design of its kind.