Curtain Wall Systems: Types of Structures and Tests

The main difference between well-designed curtain walls is that they remain waterproof throughout their life. The main structural approaches that provide curtain walls with curtain walls are highly resistant to rainwater.

Building codes require the building’s façade to provide a reliable barrier to rainwater entry. Water penetration is the most serious problem that occurs with windows and curtain walls.

Wall waterproof principles

For water to enter the building, three conditions must be met:

water on the outer surface of the wall;

holes and cracks in the wall;

driving forces.

The absence of any of these three factors precludes the penetration of water through the wall.

If rain falls vertically, the curtain wall can be protected by a sufficiently wide roof overhang, which works similar to an umbrella. However, rain rarely falls vertically. Usually it is accompanied by wind, and the principle of an umbrella no longer works. Therefore, it is impossible to design buildings that would be completely protected from the effects of rainwater. That is why not only static but also dynamic tests are carried out of the waterproofness of the hinged facades.

How wind affects walls

When designing any facade, it is important to understand how the wind can affect the building:

Direct effect of the wind. When an air stream hits a building, a pressure zone arises on its surface and the air stream changes along the surface of the facade. This gives pressure differences.

Acceleration of wind at the base of the building. This phenomenon occurs when the wind that hits the building has a higher speed near the earth's surface.

Twists. When air flows along the roof or moves along complex façade elements, zones with low air pressure (wind suction zones) are created.

Separation of air flows. Sudden changes in the direction of the air flow, for example, at parapets and corners, give suction zones with a high pressure drop. The same thing happens on the back, leeward side of the building.

Air funnels. Wind speed can increase and change direction, especially at the base of tall buildings. Tunnels and openings through buildings also create funnel-shaped air currents.

How the walls get wet

The wetting of the walls at the corners of the building is always inevitably higher than in its central parts. With a sharp change in the direction of the wind, for example, on parapets and internal corners, raindrops are separated from the air stream, which leads to a concentration of wet in these places. If the rain lasts long enough, then this water can pass through the entire wall and cause it to become very wet, including inside the building. Facades made of impermeable materials protect the wall from most of the rainwater. However, they are not able to completely exclude the penetration of water into the building.

Water penetration through walls

Each facade has many different openings, crevices and other hidden passages for rainwater. They include vertical joints to compensate for thermal expansion and various adjoining to each other of various structural elements of the walls with rubber seals installed between them.

Water flows down and along the surface of the facade under the influence of wind, until it collides with any protrusions. Then it flows along the surfaces of the corners, where most of the seams, joints and joints are located. Joints or junctions arise between various adjacent materials or individual elements from similar materials. Such joints and junctions inevitably arise in the manufacture and installation of building structures. Even when these joints and junctions are properly sealed and sealed, it is very difficult to ensure their absolute reliability throughout the long service life of the building.

Forces on the facade

The forces and phenomena that contribute to the penetration of water through the wall include:

Gravity

Kinetic energy

Surface tension

The phenomenon of capillarity

Air flows

Wind pressure

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