OBC Complex Buildings cheat sheet

Mixed-occupancy buildings are classified under one of two methods: accessory occupancies (limited area and height, subordinate to a main occupancy) or separated occupancies (fire barriers between different occupancy groups).

In the nonseparated mixed-occupancy approach, the most restrictive fire-resistance and egress requirements of all occupancies generally apply to the whole building, unless specific allowances in the code permit reductions.

An occupancy is typically 'accessory' only if it occupies less than 10 percent of the building area on a given floor and is incidental to the main use; larger areas force a true mixed-occupancy analysis.

Incidental uses (e.g., small mechanical rooms, storage, or boiler rooms) are regulated by a separate table of incidental-use requirements rather than treated as full occupancies.

High-rise classification commonly triggers at a building height greater than 75 feet above the lowest level of fire-department vehicle access, adding sprinkler, standpipe, and communication requirements.

Change of occupancy or change of use can trigger upgrades to structural, egress, and fire-protection systems even when no new construction occurs; the extent depends on the hazard index comparison.

Occupant load factors vary by use (e.g., business ~100 sq ft/person, assembly unconcentrated ~15 sq ft/person); the total load drives egress width, exits, and plumbing fixture counts.

Buildings with multiple tenants or uses should be evaluated floor-by-floor and area-by-area to confirm whether separation, sprinkler protection, or height/area increases are required.

Automatic sprinkler systems are generally required in high-rise buildings, in most assembly occupancies above a threshold occupant load, and in buildings exceeding allowable height/area limits.

Fire alarm systems must provide occupant notification (audible and visible) and often include voice evacuation in high-rise or large assembly buildings; visible alarms are required in public and common areas.

Standpipe systems are required in buildings where the highest floor is beyond a set distance above fire-department access; Class I (2.5-inch) for fire department use, Class II (1.5-inch) for occupant use, Class III combined.

Smoke control and stairwell pressurization are typically required in high-rise buildings to maintain tenable conditions in egress paths and to limit smoke spread.

Fire-resistance-rated assemblies (walls, floors, shafts) must be protected at penetrations and joints with listed through-penetration and joint systems matching the assembly rating.

Fire dampers are required where ducts penetrate rated assemblies unless an approved exception applies (e.g., certain subduct or corridor configurations); smoke dampers where smoke barriers are crossed.

Portable extinguishers must be selected and located by hazard class (A, B, C, D, K) with travel distances not exceeding code limits (commonly 75 ft for Class A, 30-50 ft for high-hazard).

Emergency and exit lighting must provide illumination for a minimum duration (commonly 90 minutes) and maintain specified foot-candle levels along egress paths.

Structural design uses load combinations from ASCE 7 (dead, live, wind, seismic, snow) with strength-level or allowable-stress methods; complex buildings often require special seismic detailing.

Buildings assigned to higher Seismic Design Categories (SDC D, E, F) require special moment frames, shear walls, or other seismic-force-resisting systems with ductile detailing.

Allowable building height and area depend on construction type (Type I through V) and whether sprinklered; Type I-A provides the greatest height/area allowances, Type V-B the least.

Fire-resistance of structural members (beams, columns, floors) must match construction type; intumescent coatings, spray fireproofing, or encasement are common protection methods.

Building envelope must control water, air, vapor, and thermal movement; continuous air barriers and proper flashing at transitions are critical to performance and durability.

Thermal performance is governed by envelope requirements (U-factors, R-values) that vary by climate zone and component; complex geometry can create thermal bridging that must be addressed.

Glazing and curtain walls must meet safety glazing requirements in hazardous locations and be designed for wind, seismic drift, and thermal movement.

Roof and floor live loads must account for occupiable roofs, mechanical equipment, and assembly uses; snow drift and rain-on-snow loads are often governing in complex roofs.

The means of egress has three parts: exit access, the exit, and exit discharge; each must maintain required width, height, and clear path.

Two exits are generally required when occupant load exceeds a threshold (commonly 50 occupants) or where a single exit is not permitted by the specific occupancy chapter.

Exit remoteness: exits must be separated by a distance not less than one-half the diagonal of the building or area served, unless a diagonal-based alternative is permitted.

Egress width is calculated from occupant load times a capacity factor (e.g., 0.2 in/person for level components, 0.15 in/person for stairs) with minimum widths (e.g., 36 in corridors, 44 in stairs).

Travel distance to an exit is limited by occupancy and sprinkler status; common limits range from 150 ft to 250 ft for nonsprinklered and up to 400 ft in some sprinklered cases.

Accessibility requires an accessible route from arrival points to all accessible spaces, with compliant door clear widths, maneuvering clearances, and accessible means of egress in high-rise buildings.

Stairways must meet dimensional rules (riser/tread proportions, handrail heights, landings) and have proper enclosure ratings when serving as exits.

Exit signs and path-of-travel marking must be visible and illuminated, and doors in the egress path must swing in the direction of travel when serving large occupant loads.

Plumbing fixture counts are derived from occupant load and use (e.g., water closets, lavatories, drinking fountains) using a fixture-ratio table; accessibility requires at least one accessible fixture per type.

Mechanical systems must provide required outdoor air ventilation per occupant and use, and exhaust for specific spaces (restrooms, kitchens, laboratories) at code-specified rates.

Shafts and chases for MEP systems must respect fire-resistance ratings; duct and pipe penetrations require listed firestop systems.

Electrical service and distribution must be coordinated with equipment loads, emergency power (generators or UPS) for life-safety loads, and required clear working space around panels.

Elevators serving as accessible routes must meet size and door requirements; in high-rise buildings, at least one elevator must be served by standby power for firefighter and occupant use.

Coordination of ceiling plenums: ducts, sprinklers, and lighting must maintain required clearances and not obstruct sprinkler spray patterns or exit signage.

Emergency power systems must be tested and maintained; life-safety branches (egress lighting, fire alarm, fire pump) must be separated from optional standby loads.

Kitchen hood suppression, grease ducts, and make-up air must be coordinated with the fire protection and mechanical designs to satisfy both life safety and building code requirements.

Plan review verifies compliance with building, fire, accessibility, and energy codes before permit issuance; complex buildings often require concurrent review by multiple disciplines.

Permits are required before construction, alteration, or change of use; work started without a permit may require stop-work orders and additional inspections or penalties.

Inspection milestones typically include foundation, framing, rough-in (MEP), insulation, and final inspection; each must be requested and passed before the next phase.

Special inspections (e.g., structural welding, high-strength bolting, post-installed anchors) are required where the code mandates them and must be performed by approved agencies.

Fire-resistance-rated construction inspections verify that rated assemblies, firestopping, and dampers are installed per approved plans before concealment.

Certificate of occupancy is issued after final inspections confirm the building complies with approved plans and is safe for its intended use.

As-built changes that deviate from approved plans require revised drawings and re-review; field changes cannot substitute for approved permits.

Recordkeeping: inspection reports, test results (fire alarm, sprinkler, emergency power), and special inspection reports must be retained and made available to the code official.