Appeal 34808

ORSC R302.1 R302.3

Walls less than 6 feet from adjacent structures must be protected with not less than one-hour fire-resistance-rated construction applied to the interior face of the wall assembly.

Use of two layers of 5/8” Type X gypsum board on the exterior face of both the ADU and stairway structures in lieu of applying it to the interior.

Install two layers of 5/8" Type X gypsum board on the exterior face of each wall (ADU and stairway). The assemblies are fully covered with continuous Type X board, providing 1-hour protection on each side, totaling a 2-hour rated separation. All other code-required fire-resistive materials and layers will be maintained.

• Interior installation would require demolition of:
o A finished ADU bathroom with tile, toilet, sink, and plumbing.
o The entire stair structure, including treads, risers, and stringers.
• The proposed method maintains full code-required fire-resistance while avoiding substantial tenant disruption, plumbing demolition, and structural removal.
• Life safety and fire-resistance intent are preserved or exceeded by providing continuous exterior 1-hour assemblies on both structures.

ORSC R403.1 R302.1 R302.2

Fire-rated walls must be supported by continuous foundation walls with properly sized footings per the structural load path.

Use of reinforced piers and structural steel beams (C8x10.5), including fire-rated decking, to support a 2" wide firewall in lieu of a continuous foundation wall.

• Retain and reinforce existing piers.
• Bolt short sections of galvanized C8x10.5 beams to piers.
• Span a continuous galvanized C8x10.5 beam (~13’6.5”) under the firewall.
• Mount a 2" wide fire-rated wall above this beam (¾" plywood + 2 layers ?" Type X + non-combustible cladding).
• Infill 15” between stair stringer and ADU with fire-rated galvanized plate supported on beam and steel angle.
• Maintain utility clearance under assembly.

• A continuous foundation would require full demolition of the existing stair structure and rerouting of active sewer, gas, water, lines—all of which were installed with the original ADU permits.
• The proposed beam-and-pier configuration avoids significant tenant disruption, demolition, and excavation, while preserving pre-existing utility routing.
• The wall is fully fire-rated, structurally supported on non-combustible materials, and remains structurally independent from both the ADU and stair system.
• Utility Clearance: The proposed configuration preserves necessary clearance and access for existing sewer, water, gas, and roof drainage lines that run between the house and ADU beneath the stair structure. The design avoids enclosing these lines and ensures they remain accessible for inspection and future maintenance. Existing utility elevations and alignments are unchanged from their original permitted installation.
• This approach meets the intent of the structural and fire separation provisions of the ORSC, providing equivalent life safety and durability while minimizing disruption to permitted and functional systems.