OBC Large Buildings cheat sheet

The building code is a minimum-standard document: compliance with its provisions establishes the minimum acceptable level of safety for a building, not an optimum or recommended level.

Objectives of the code include safety, health, accessibility, fire and structural protection, and environmental separation; a solution must satisfy every applicable objective, not just one.

A building must be designed and constructed as a single integrated system; compliance of individual components does not by itself establish compliance of the assembly.

Where two provisions conflict, the more restrictive provision governs unless the code expressly states an exception or an alternative-solution route applies.

Alternative solutions must achieve at least the level of performance intended by the acceptable solutions, supported by documented analysis and accepted by the authority having jurisdiction.

Terms defined in the code prevail over ordinary dictionary meanings; undefined terms take their commonly understood meaning consistent with the code's intent.

Compliance is assessed at the time of permit, during construction, and at final inspection; later changes of use or occupancy may trigger new compliance obligations.

The code applies to new construction, additions, alterations, and changes of use, with separate rules for each; existing buildings are not automatically required to meet new-construction standards.

Building height is measured from grade to the highest finished floor level of the top storey, excluding rooftop mechanical penthouses and similar non-storey projections.

Building area is the greatest horizontal area of the building above grade, measured within the exterior faces of exterior walls, projected over the building footprint.

Storey means the space between two successive floor levels, or between a floor level and the roof; mezzanines count as storeys when they exceed the permitted area threshold.

Floor area versus building area: floor area is measured per storey for occupant-load and egress calculations; building area is used for size and construction-type limits.

Occupant load is the number of persons for which a space is designed, computed from floor area divided by the occupant-load factor for that use, or from fixed seating counts.

Grade is the lowest of the average finished ground levels adjacent to the building; where ground slopes, the average is taken over the building perimeter.

An exit is a continuous protected path from the floor area to a public way; a corridor or aisle leading to an exit is not itself an exit.

A firewall divides a building into two buildings for code purposes; a fire separation divides portions of one building and does not create separate buildings.

Fire-resistance ratings are expressed in hours and are determined by standardized fire tests or by accepted fire-resistance design methods such as listed assemblies.

Fire separations must have a fire-resistance rating not less than the required rating of the assembly they protect, and openings must be protected by closures rated to the same separation.

Combustible construction limits are controlled by permitted building height and area, sprinkler protection, and the occupancy classification of the building.

Automatic sprinkler systems permit increases in building height and area and reductions in required fire-resistance ratings and separation distances, subject to the code's specific allowances.

Spatial separation from property lines and exposing buildings is measured from the building face to the lot line, with permitted reductions where the facing wall has limited unprotected openings.

Fire alarm systems must be provided where required by occupancy and building size; the system must include detection, notification, and annunciation appropriate to the building's use.

Smoke control is required in certain large or high buildings, including atria and interconnected floor spaces, using pressurization, exhaust, or a combination of methods.

Standpipe and hose systems are required in buildings exceeding specified heights or areas, with hose stations located so that every point of the floor area is within the code's hose-stream reach.

Means of egress comprises three parts: exit access, the exit itself, and exit discharge; each part must be continuous, unobstructed, and of sufficient width for the occupant load.

Egress width is computed from occupant load multiplied by the per-person width factor; the required capacity is the greater of the stair or level-component calculation.

Travel distance to an exit is measured along the path of egress travel, not in a straight line, and is limited by occupancy and by whether the building is sprinklered.

Two means of egress are generally required where occupant load, travel distance, or common-path limits are exceeded; the two exits must be remote from each other by the required separation.

Accessibility requires an accessible route from the public way to the building entrance, to all normally occupied spaces, and to accessible washrooms, parking, and services.

Accessible washrooms require turning space, grab bars, accessible fixtures, and clear floor space at each fixture; the door must not swing into the required clear space.

Ramps require landings at top and bottom and at changes of direction, edge protection, and handrails on both sides where the ramp rises above the threshold height.

Guards are required at openings and at the edges of floor areas where the difference in level exceeds the code threshold, with guard height and opening limits specified.

Limit-states design compares factored resistance to factored load effects; the design must satisfy both ultimate limit states and serviceability limit states.

Load combinations combine dead, live, snow, wind, and earthquake effects with specified load factors and companion-load coefficients.

Dead load is the weight of all permanent construction and fixed service equipment; live load is the occupancy-related load, with specified minimum values by use.

Snow load design considers ground snow load, exposure, thermal, and importance factors, plus drift loads at changes in roof height and at parapets.

Wind load depends on basic wind pressure or speed, exposure category, building height, and internal pressure coefficients for enclosed and partially enclosed buildings.

Seismic design uses the site's spectral acceleration values, the building's seismic force-resisting system, and its ductility and overstrength factors.

Deflection limits are serviceability criteria applied to floors, roofs, and cladding supports to prevent cracking, ponding, and damage to finishes.

Structural drawings and specifications must be sealed by a qualified professional, and field reviews must confirm that construction conforms to the designed structural system.

The building envelope must separate interior from exterior conditions and control heat flow, air leakage, moisture movement, and precipitation ingress.

Thermal performance is expressed as an effective thermal resistance or U-value for the assembly, accounting for thermal bridging at framing and structural penetrations.

Air barriers must be continuous across the envelope and must be sealed at joints, penetrations, and interfaces with other assemblies.

Vapour barriers are positioned on the warm side of insulation in cold climates; their need and location depend on the assembly's moisture analysis.

Rain penetration control uses the principle of deflection, drainage, and drying: shingles and flashings shed water, and a drained cavity provides a secondary line of defence.

Window and door performance is rated by condensation resistance, watertightness, air leakage, and structural capacity, and must suit the building's exposure.

Roof assemblies must drain to drains or scuppers sized for the design rainfall intensity; ponding must be checked for stability on flexible roofs.

Envelope penetrations for ducts, pipes, and structural connections must be sealed and insulated to maintain continuity of air, vapour, and thermal control layers.

Energy efficiency provisions set minimum requirements for the building envelope, HVAC equipment, service water heating, lighting, and electrical distribution.

The building envelope's thermal transmittance and air leakage are limited by climate zone and by the ratio of glazed area to gross wall area.

HVAC equipment efficiency is governed by minimum performance ratings, and systems must be sized using recognized load calculation methods rather than rules of thumb.

Demand control ventilation and economizer provisions apply where occupant density and climate conditions make them effective energy measures.

Lighting power density limits are set per space type; automatic controls are required for spaces with irregular occupancy and for daylighted zones.

Environmental separation addresses sound transmission, vibration, and indoor air quality as well as heat and moisture; airborne and impact sound insulation are both regulated.

Sound transmission ratings between dwelling units and between units and common spaces are set by the code's apparent sound transmission class and impact insulation class limits.

Ventilation must supply outdoor air at rates based on occupancy and floor area, and exhaust must remove contaminants at their source in kitchens, washrooms, and parking areas.

Occupancy classification groups buildings by use and by the hazard to occupants, and it drives height, area, construction type, egress, and fire protection requirements.

Major groups include assembly, institutional, residential, business and personal services, mercantile, industrial, and storage occupancies, each with subdivisions.

Assembly occupancies are further divided by occupant load and by whether seating is fixed or non-fixed, which affects egress and travel-distance limits.

Institutional occupancies are divided by whether occupants are capable of self-preservation without assistance, which controls sprinkler and egress requirements.

Residential occupancies distinguish dwelling units, sleeping rooms, and transient accommodation, with different fire separation and alarm requirements for each.

Mixed occupancies are treated either as separate occupancies with fire separations between them or as a single occupancy with the most restrictive requirements applied.

A change of use requires re-evaluation of the occupancy classification, and the new use must comply with the requirements applicable to that classification.

Occupant load determines egress capacity and is calculated per space; where a space has multiple uses, the use producing the greatest load governs.

Building size is limited by the combination of occupancy classification, construction type, building height, and building area, with sprinkler allowances.

Construction types range from noncombustible to combustible, and each type carries permitted limits on height and area for each occupancy group.

Combustible construction is permitted only within the height and area limits set for the occupancy; exceeding them requires noncombustible or protected construction.

Sprinklered buildings may be permitted greater heights and areas than unsprinklered buildings, and may use reduced fire-resistance ratings for structural elements.

A firewall may divide a building into two code buildings, each of which must independently satisfy the size limits for its occupancy and construction type.

Mezzanines are limited in area relative to the storey below and must be open to that storey, or be treated as a separate storey with full egress and separation.

Unprotected openings in exterior walls are limited by spatial separation from the lot line and by the fire-resistance rating of the facing wall.

Rooftop equipment and penthouses are excluded from height measurement but are limited in area relative to the roof and must meet structural and fire requirements.

Every building must have sanitary facilities sized to the occupant load and the occupancy type, with separate facilities provided where required.

Washrooms must be ventilated, finished with cleanable surfaces, and provided with hot and cold water at handwashing sinks.

Drinking water must be provided at a rate based on occupant load, and the fixtures must be accessible and maintained in operating condition.

Fire alarm and detection systems must be designed to warn occupants, summon the fire service, and initiate emergency procedures appropriate to the occupancy.

Emergency lighting and exit signs must be provided on egress routes and must operate for the required duration on failure of normal power.

Firefighting access routes, hydrant locations, and siamese connections must be provided and maintained clear for fire department use.

Refuse and recycling storage must be enclosed, ventilated, and separated from occupied spaces by construction meeting the required fire-resistance rating.

Life safety systems, including sprinklers, alarms, and smoke control, require inspection, testing, and maintenance at the intervals set by the applicable standards.

Plumbing systems must be designed for the fixture units served, with pipe sizing based on the demand of the fixtures and the available pressure.

Drainage systems require venting to protect trap seals; every fixture must have a trap, and the vent must extend to outdoor air.

Storm drainage must be sized for the design rainfall intensity, and roof drains must be provided with strainers and secondary drainage or overflow.

Mechanical systems must provide ventilation, heating, and cooling adequate for the occupancy, and combustion appliances must have adequate air supply and venting.

Duct and pipe penetrations through fire separations require listed fire dampers or firestop systems rated to the separation.

Electrical systems must provide capacity for the connected load, with service equipment, overcurrent protection, and grounding designed to the electrical code.

Emergency power must be provided for life safety systems where required, including fire alarm, emergency lighting, and fire pump service.

Elevators must be provided where the building height or occupant needs require them, and at least one must be accessible and sized for stretcher use.

High buildings require additional measures: smoke control, stairwell pressurization, emergency power, and voice communication where the height exceeds the code threshold.

Interconnected floor spaces and atria require smoke control analysis demonstrating that smoke will not compromise egress from any occupied level.

Alternative solutions may substitute for acceptable solutions where the proponent demonstrates equivalent performance through analysis, testing, or engineering judgement.

An alternative solution must address every objective and functional statement relevant to the proposed deviation, not only the specific provision being replaced.

Performance-based design for large buildings typically includes fire modelling, egress modelling, and structural response analysis under design fire scenarios.

Fire safety plans and emergency procedures are required for large buildings and must be maintained and updated as the building's use changes.

Post-disaster buildings must remain operational after a design earthquake, requiring enhanced structural and mechanical robustness.

Commissioning of life safety and mechanical systems verifies that installed systems perform as designed before the building is occupied.

A building permit is required before construction, alteration, or change of use, and the application must be accompanied by drawings and specifications sufficient to show compliance.

Drawings and specifications must be prepared and sealed by a registered professional where the work affects structural safety, fire safety, or health.

The authority having jurisdiction may require supporting calculations, test reports, or an alternative-solution submission before issuing a permit.

Field reviews by the designer confirm that construction conforms with the sealed documents; deficiencies must be reported and resolved.

Inspections at defined stages, including foundation, framing, and final, must be passed before the work proceeds or the building is occupied.

Changes during construction that affect compliance require revised drawings and, where significant, an amended permit.

An occupancy permit or equivalent authorization is required before a building is occupied, following confirmation that life safety systems are operational.

Professionals have a duty to report unsafe conditions and to refuse to certify work that does not conform to the code or to their sealed documents.