| Research Program
Performance Criteria
The performance of the rainscreen system is defined qualitatively in many publications, but for commissioning purposes, its performance must be defined quantitatively. Unlike mechanical systems, the rainscreen is not composed of rated and tested components and there is no defined performance rating. The performance required to control rain penetration and to reduce cladding loads for a possible structural benefit has not been previously identified. However, based on laboratory experience and field observations, it is suggested that 80% pressure equalization under static load, 50% pressure equalization under a 2 Hz dynamic load, and a maximum air leakage rate of 0.1 L/s m2 @ 75 Pa be established as recommended rainscreen performance criteria until better information is obtained through research. These values provide a point for departure for the engineering and commissioning of any rainscreen system.
The Commissioning Process
If the performance of a rainscreen wall/window is to be designed and constructed to performance criteria, the normal process of design and construction must be expanded to include engineering and commissioning procedures for the rainscreen system. Such a process is outlined below.
In the normal course of design, cladding systems are selected during the development of facades. It is at this stage that the decision to use a rainscreen wall must be made. The vertical and horizontal compartments must be located and the number of rainscreen cavities determined.
Having chosen the rainscreen principle for the exterior walls, the performance criteria must be established, including the steady state and dynamic equalization performance and the ratio of rain penetration to rain loading.
The individual parts of the rainscreen wall must be designed, including an air barrier system, compartment seals, and a cladding system with vents and drains.
The steady state equalization and the dynamic performance must be determined using Version 2.0 of the CMHC RAIN* computer program. If the design fails to meet the established criteria, it is revised until the criteria are met. If the performance criteria are met, the design is carried to the production of working drawings.
The commissioning criteria should be established, which could include:
a maximum limit on the air barrier/compartment seal leakage,
a minimum cladding vent area,
a maximum time decay rate for the prescribed CEM tests, and
a maximum limit on the deflections of the cladding and air barrier system.
The design must be validated, ideally through laboratory testing of a full-scale mock-up, to determine if the performance requirements of the simulation compare adequately with the mock-up performance and what quality of construction was required.
If the mock-up fails to meet the performance objectives, then it is progressively revised and retested until it does. On the final iteration, the CEM (Cavity Excitation Method) performance characteristics (decay curve) are defined for the field commissioning criteria.
If timing or budget do not permit the laboratory testing, a mock-up could be done on site. However, an allowance must be carried for modest re-design as the builder should not be expected to pay for the uncertainty of design changes. The design must be validated before the builder accepts responsibility for the eventual commissioning specifications of the rainscreen system.
The commissioning process would then be undertaken to determine compliance of the rainscreen. Commissioning may proceed in a progressive manner if the project is large and complex, or near the completion of construction if adequate site supervision has ensured that the quality of construction required was attained as per laboratory or mock-up requirements.
If the construction has met the commissioning criteria, then a certificate of compliance may be issued by the commissioning agent or architect to the builder.
While the commissioning procedure does not include a water test, it would be prudent to undertake such a test. | 
