The Rainscreen Association in North America announced that Graham Finch of RDH will be presenting on how and why rainscreen walls work or when they don’t at the RAiNA Conference in Chicago on Nov. 7.
Rainscreen walls are systems made up of several materials that come together as a minimum building enclosure function to protect buildings from rain. Rainscreens must also manage environmental loads, including structural loads, fire and smoke, UV radiation, sound, heat flow, airflow and vapor movement. Each of the system components, including the airspace between the outer and inner layers (aka the cavity or gap), are important to performance – and they need to work together to be effective.
The outer finish/cladding is the most visible rainscreen layer. This layer sheds water and provides the first line of protection of the underlying materials from the environment. If cladding gaps are added to an open rainscreen, extra water and UV get past the outer layer, which should be managed with carefully selected materials and details. The structural attachment of the cladding through sub-framing and cladding attachments, and often exterior insulation, requires a thoughtful design that is balanced for thermal performance and structural efficiencies. Hidden behind the cladding is the critical airspace – the one “free” rainscreen component. This gap provides a clear path for water drainage and airflow through openings to the exterior. Most of the time, this system keeps the wall dry. If the air gap is oversized or attention isn’t taken with the selection of cladding or other materials, then this hidden cavity can become a fire concern. If the gap is too small, water can get trapped or airflow can be restricted, hindering performance. An inner water-resistive layer completes the rainscreen and acts as the last line of defense from water, and it may also control airflow and vapor. Insulation placed within the rainscreen cavity for thermal benefit may widen the gap and impact water control decisions, and the insulation materials may also have fire code ramifications. Some designers talk about pressure equalization as a solution for additional water management but find it difficult to achieve in practice. Pest management must also be considered in the openings and details, and these screen openings can even tie into wildfire-resistant construction details for rainscreen walls.
Needless to say, a lot is going on within a rainscreen wall. This presentation uncovers how rainscreen walls work at a fundamental level and gets into the key design and construction considerations that make them perform as intended.
