A structural multi-tasker, the building envelope is required to perform a host of functions. It provides structural integrity, moisture control, insulation and, of course, serves as the aesthetic “face” of the building. Modern wall design has moved toward consolidating multiple functions into as few layers as possible. The curtain-wall configuration may be the culmination of this progression with a single layer of materials intended to execute the wide breadth of functions.

This consolidation of multiple functions into a single layer often requires making trade-offs between material performance and design flexibility by requiring a layer to act as a jack-of-all-trades and master of none, as the adage goes. Architects may have to rely on materials to accomplish more than they were designed to do, which may lead to a compromise in the original design intent or in the long-term performance of the building itself, including mold problems and the associated health risks.

Rainscreen construction is one tool available to architects that allows them to achieve optimal building performance without sacrificing design flexibility. Rainscreen — a configuration in which the cladding is separated from a building’s weather-resistant barrier by means of a flashed and drained cavity — enables each building layer to be designed for a specific function. This gives architects the ability to optimize each layer around fewer variables resulting in a significantly higher performing façade.

Enlarge this picture The optimized rainscreen configuration separates cladding and moisture- and thermal-control layers from the exterior of the structure.

A typical building envelope utilizing rainscreen construction includes the following layers, from exterior to interior:

• Rainscreen (aesthetic layer and first line of moisture defense);
• Ventilated air cavity;
• Exterior insulation;
• Moisture-control layer (second line of defense); and
• Steel stud and sheathing (structure).

The rainscreen layer itself is the first critical component in achieving a high-performance façade. For optimal performance, rainscreens must

1. Control the bulk of the rainwater that comes in contact with the building;

2. Be properly ventilated to ensure sufficient airflow within the cavity (avoiding mold/mildew issues or other water-damage issues); and

3. Have a supporting system to allow for proper air circulation and water management such as vertical or horizontal channels.

With separate layers behind the rainscreen providing thermal performance, moisture control and structural integrity, the architect is given exceptional freedom with the aesthetic design of the building’s exterior.

This fusing of form and function can be seen in Harvard University’s newest 226,800-square-foot addition to the Center for Government and International Studies. Located in Cambridge, Mass., superior temperature and moisture control were imperative in the creation of a structure that would stand the test of time.

The surrounding array of statement-making architecture also called for a traditional yet eye-catching design. Architect Pei Cobb Freed & Partners worked with NBK Ceramic to develop a high-performance rainscreen façade using optimized layers to achieve improved moisture control, thermal performance and energy efficiency. From afar, the custom cladding profile suggests a subtle gradient in texture, while closer inspection reveals the effect is created with contiguous seams of baguette tiles wrapping the building — windows included. The result is a striking and unique high-performance façade — no compromise necessary.