Key Components and Features
1. One-Hour Wall Assembly
The wall is composed of two separate, one-hour rated assemblies forming a double wall system. Each wall section acts independently to resist fire spread for at least one hour, offering additional safety through redundancy. Importantly, the design allows for plumbing and mechanical ducts, making it practical and functional for multifamily construction.
2. Continuous Fire Wall to Roof Sheathing
A major detail in this design is the continuity of the firewall up to the roof sheathing. This ensures that the fire barrier remains intact even if the ceiling below is not protected by 5/8” Type X gypsum board. Maintaining continuity from the foundation to the roof is essential for preventing fire from bypassing through structural cavities or attic spaces.
3. Air Space Between Assemblies
An intentional air gap separates the two wall assemblies. This air space serves two purposes:
- It enhances sound insulation between units.
- It adds an extra layer of fire resistance, acting as a break in heat transfer between walls.
4. One-Hour Floor-Ceiling Assembly
The wall connects seamlessly to a one-hour rated floor-ceiling system, ensuring a consistent fire rating across vertical and horizontal separations. This detail provides protection not just between adjacent units but also between stacked floors.
5. Fire-Rated Gypsum Board (Type X)
The specification of 5/8” Type X gypsum board at the rim joist and other critical junctions adds to the fire performance of the system. Type X boards are designed to resist heat and maintain structural integrity longer under fire exposure.
6. Concrete Slab or Foundation Wall
At the base, the wall extends down to the concrete slab or foundation wall, completing the continuous barrier from ground to roof. This ensures that the firewall remains unbroken, a requirement for compliance with building safety codes.
Purpose and Function
This wall detail serves as an educational reference for architects, engineers, and builders. It clearly demonstrates how to achieve code-compliant fire and sound separation in multifamily buildings. By using durable, rated materials and maintaining continuity, the design ensures that fire does not spread between adjoining units or floors — a vital factor in occupant safety and regulatory approval.
The design aligns with standards recommended by the Building Science Corporation (BSC), known for advancing building performance and safety practices.
Why It Matters
In multifamily housing, the stakes are high — fire separation walls are not just a code requirement but a life-saving feature. They protect residents, minimize property damage, and help contain fire to its source. Properly detailing such walls can be the difference between a small contained fire and a catastrophic event.
Our Role
At County Permit Drawings, we specialize in delivering detailed, code-compliant design solutions — from architectural and structural plans to MEP and 3D visualizations. Our team ensures every drawing aligns with safety standards and regulatory expectations.
