While giving a presentation, a contractor asked me two questions. I found out later that several in attendance had the same questions but no one else asked. I thought it would be of value to post them here.?
1)????? What is the difference between an air barrier?and a?rainscreen?
2)????? Are they both required in single or multifamily buildings by code?
The answer to the second question would depend on which code you are adhering to; however, many professionals believe that “Best Work Practices” is using a code no later than one issue back. Following that logic, it would be the International Residential Code 2021 (IRC 2021) since IRC 2024 is now out. So, the answer could be yes.?
?Both serve distinct purposes in building single and multifamily construction:?
- An?air barrier?is a component of a building envelope. It prevents air from passing through the walls and protects the structure from moisture intrusion. Does not specifically allow it to drain.
- Significant changes were made in the?2012 International Building Code (IBC), 2012 International Energy Conservation Code (IECC), and ASHRAE 90.1-2010 which required the design of buildings to not only have increased thermal efficiency with the use of continued insulation, but also require the use of a complete air barrier system to address air leakage.
- It acts as the final line of defense against water infiltration, ensuring that conditioned indoor air stays inside, and unconditioned outdoor air stays outside.
- The?air barrier?system typically includes materials such as membranes, tapes, sealants, and sheathings.
- In cases where the wall is exterior,?a rain screen is required per IRC 2021 and IRC 2024.
- What is a Rainscreen:
- No one product is a rain screen!
- A?rainscreen?is also a crucial part of an exterior wall detail designed to remove moisture and improve the performance of cladding systems. Required in the IRC codes 2021 and 2024.
- The purpose of the?rainscreen?system is to:
- Create a gap, preventing water from wicking into the building.
- This gap must be a minimum of 5mm between the outer cladding (siding) and the inner layer (sheathing) of the wall.
- Must allow drainage and evaporation, enhancing moisture management.
- The?rainscreen?system at a minimum consists of the following components:
- Outer Cladding Layer: This layer forms the external finish of the wall and sheds water.
- Air Space/Gap: Found between the outer and inner layers, this cavity can have three types of material per ASTM E2925. Type A) Entangled netting, Type B) A formed dimple sheet, Type C) an engineered Batten strip. These products must be more than 5mm in width and 90% open construction to promote ventilation and drying.
- Water Resistive Barrier (WRB): The inner layer, which may include, tapes, sealants, building wrap, and sheathings.?
In summary, while both serve essential roles in building performance, an?air barrier?focuses on air flow, while a?rainscreen?system stops moisture from entering the house and allows the moisture to drain or evaporate, not remain in the wall. A rain screen system will work with all types of cladding. Both are required by code depending on local code adoption. Please check your local code enforcement regulations.
