Watertightness: What Is It and Why Does It Matter?
Heavy rain, especially when accompanied by strong winds, puts windows and balcony doors to the test. How effectively do they prevent water from entering a building? The answer lies in their watertightness, a performance characteristic worth understanding when choosing windows and doors.
What Is Watertightness?
Watertightness is the ability of a closed and locked window or external door to prevent rainwater penetration under specified conditions. It concerns both the rain falling onto its surface and the effect of wind, which drives water towards joints and seals.
This performance is assessed through laboratory testing. Water is sprayed onto the external face of the window or door while the air pressure difference between the outside and inside is gradually increased to simulate the effect of wind. The European standard EN 1027 specifies how the test is carried out, while EN 12208 defines how the result is assigned to a watertightness class.
The class indicates the maximum test pressure at which the window or door prevented water penetration. For example, Class 9A indicates successful testing at 600 Pa, while Class E750 indicates successful testing at 750 Pa. Pascals (Pa) are a unit of pressure, not a measure of rainfall. When comparing results obtained using the same test method, withstanding a higher pressure without water penetration indicates better performance. These ratings help guide the selection of a suitable window or door according to the opening’s exposure to wind and rain.
How Does It Work?
Protection against water depends on the different components of the window or door working together. Sealing gaskets protect the contact points between components, while the locking mechanisms help the window sash or door leaf close securely against the frame.
The system also incorporates designed drainage paths. Any water that enters the outer drainage zone of the frame is directed back outside through dedicated drainage openings. These are essential to the system’s operation and must remain clear.
The joint between the frame and the building is equally important. Even a high-performing window or door can allow water to enter around its perimeter if this connection is not properly sealed during installation.
Why Does It Matter in Practice?
Effective watertightness protects walls, floors and internal finishes from water ingress. It helps prevent staining, blistering paint and damage to materials, keeping interiors dry and reducing the need for repairs.
However, not every opening has the same requirements. The building’s location and height, along with the façade’s exposure to wind and rain, influence the performance needed. A window sheltered by an overhanging balcony may face different conditions from a balcony door on an exposed façade.
This makes it important to check the technical documentation for the specific window or door configuration being selected. The performance of a tested window or door does not automatically apply to every size or opening type within the same system.
What Can Affect Its Performance?
Over time, worn gaskets, hardware that needs adjustment or blocked drainage openings can reduce protection against water. Cleaning and periodic checks, in accordance with the manufacturer’s instructions, help maintain proper operation.
If a leak occurs, a qualified professional should first identify its source. Applying sealant without investigating the cause may fail to resolve the problem and could block the intended drainage paths.
Myths and Facts
Myth: “Water droplets on the inside of the glass mean the window is leaking.”
Fact: The droplets may be caused by condensation, which occurs when moisture in the indoor air condenses on the cold glass surface. This is different from rainwater entering through the window.
Myth: “Water in the frame means there is a problem with the window or door.”
Fact: Water in the designated outer drainage zone does not, by itself, indicate a fault. The system is designed to direct this water back outside through dedicated drainage openings, which must remain clear.
Myth: “A high watertightness class also guarantees protection against flooding.”
Fact: Watertightness testing assesses resistance to rainwater penetration under a specified air pressure difference. Flood resistance involves different conditions and requires a separate assessment.
Conclusion
Watertightness is an important consideration when choosing windows and doors. Its value becomes clear in everyday use: interiors stay dry and surfaces remain protected when the weather takes a turn.
At ETEM, technical documentation supports the selection of aluminium systems suited to the requirements of each project. With an appropriate system, careful fabrication and correct installation, tested performance translates into effective protection.
