Commercial Building Inspector B2Wall Construction and Wall CoveringsMedium
A commercial building inspector is reviewing the exterior wall finishes for a new retail store. The plans specify stucco applied over a wood-framed wall. What is the minimum number of layers of weather-resistive barrier required behind the stucco, where the lath and plaster are not separated from the sheathing by an air space?
- AOne layer of No. 15 asphalt felt
- BOne layer of Grade D building paper
- CTwo layers of No. 15 asphalt felt or equivalent
- DA fluid-applied membrane only
Show answer & explanationAnswer & explanation
Correct answer: C. Two layers of No. 15 asphalt felt or equivalent
According to IBC Section 1404.2, for exterior walls with stucco where the lath and plaster are not separated from the sheathing by an air space, a minimum of two layers of No. 15 asphalt felt or an approved equivalent is required as the weather-resistive barrier.
Why the other options are wrong
- A. One layer of No. 15 asphalt felt is typically not sufficient for stucco applications without an air space.
- B. Grade D building paper is often equivalent to No. 15 felt, but two layers or equivalent performance is still required.
- D. While fluid-applied membranes can be approved, the prescriptive requirement often specifies the felt layers, providing a baseline.
Stucco Weather-Resistive Barrier
A robust weather-resistive barrier is crucial behind stucco, especially without an air gap, to prevent moisture intrusion into the wall assembly and ensure long-term durability.
- Protects against bulk water penetration.
- Minimum two layers of No. 15 felt or equivalent (IBC 1404.2).
- Essential when no air space is provided for drainage.
Memory trick: Stucco's Shield: Layers for Leakage's Limit.