An inspector is reviewing a proposed exterior insulated finish system (EIFS) for a commercial building. The EIFS is specified to use drainage EIFS. What type of weather-resistive barrier is typically required behind a drainage EIFS system, as per general IBC requirements for exterior walls?
- AA vapor barrier with a perm rating of less than 1.0
- BA single layer of No. 15 asphalt felt
- CA minimum of two layers of No. 15 asphalt felt or equivalent
- DA fluid-applied membrane specifically designed for EIFS drainage
Show answer & explanationAnswer & explanation
Correct answer: C. A minimum of two layers of No. 15 asphalt felt or equivalent
According to IBC Section 1404.2, for exterior walls, a weather-resistive barrier is required. For most exterior wall coverings susceptible to moisture penetration, including EIFS (especially drainage EIFS which relies on this barrier), a minimum of two layers of No. 15 asphalt felt or an approved equivalent is typically required. While fluid-applied membranes are used, the specific code requirement often defaults to the two-layer felt or equivalent performance.
Why the other options are wrong
- A. A vapor barrier is distinct from a weather-resistive barrier and serves a different function (managing vapor diffusion, not bulk water).
- B. A single layer of No. 15 asphalt felt is generally not sufficient for exterior walls requiring a robust weather-resistive barrier, especially with EIFS.
- D. While fluid-applied membranes are used and can be approved, the code's baseline often refers to the prescriptive felt layers or an equivalent performance, making 'two layers of felt' a more direct code answer for typical requirements.
EIFS Weather-Resistive Barrier
A weather-resistive barrier (WRB) is a critical component behind exterior wall claddings like EIFS, providing a secondary plane of protection against bulk water penetration into the wall assembly.
- Protects the sheathing and framing from moisture.
- Essential for drainage EIFS to function correctly.
- Typically requires two layers of No. 15 felt or equivalent performance (IBC 1404.2).
Memory trick: Barrier's Bulwark: Bulk Water Blocked By Basic Barrier.