Water ingress is a perennial problem of owners of steel buildings. The penetration of rainwater and the resulting entrapped moisture, which may cause mold and corrosion, have increased the demand for rainscreen wall systems for steel buildings.
Rainscreen cladding systems used in steel buildings, adhere to the common concept of modern engineering that it is more beneficial to work with nature rather than against it.
The system works by allowing the ingress of air at the base and the egress of air at the top.
Rainscreen systems for steel buildings consist of an outer panel, a ventilated cavity, and an inner leaf. The outer leaf sheds and controls most of the rainwater, while the inner leaf performs an array of functions such as
1. final moisture barrier
2. air/vapor barrier
4. building structural wall.
Through open joints, the outer leaf allows penetration of rainwater. Now, the volume of penetrating water varies depending on the design principle used which can be either be one of these two approaches, the drained/back-ventilated approach (D/BV) or the pressure-equalized/ compartmented (PER) approach.
The Metal Construction Association differentiated these two techniques in the in the document entitled, Understanding the “Rainscreen Principle. The body felt that a clarification is necessary on this matter since there are hybrid versions of Rainscreen systems for steel buildings that combine both approaches. These systems place air and water tightness specifications on the outer leaf, which contradicts the basic principles of the “Rainscreen” theory.
The stand of the MCA is mostly based on the book Rainscreen Cladding: A Guide to Design Principles and Practices, which clearly made a distinction between the two techniques. The D/BV approach involves draining off most of the rainwater at the outermost surface of the wall and providing a cavity for drainage and evaporation of the remainder. The PER approach aims to eliminate the penetration of rainwater by leaving some or all of the joints open to the passage of air, but not of rainwater.
Both of these systems can be used successfully for steel buildings. However, building owners must be careful not to opt for hybrid versions, which may not perform as expected.