BC Building Code Part 9 vs Part 4: When Is a Structural Engineer Required?

Understanding BC Building Code Part 9 vs Part 4 is important before structural drawings are prepared or a permit is submitted. A project may qualify as a Part 9 building and still contain structural components that require Part 4 engineering.

The official BC Building Code 2024 page applies to most of British Columbia. Vancouver uses the Vancouver Building By-law 2025, with additional professional requirements in some situations.

by Merah Putih

Part 9 Buildings in British Columbia

Part 9 of Division B covers housing and small buildings that are no more than three storeys in building height, have a building area not exceeding 600 m², and fall within the permitted Group C, D, E, F2, or F3 major occupancies.

It provides prescriptive requirements for common construction conditions, including framing, foundations, and lateral bracing within Code limits.

A structural engineer is not automatically required for every Part 9 building. Registered professionals are required only in certain situations.

Part 4 Structural Design Requirements

Part 4 provides the engineering design framework for buildings and structural components within its scope. Within a Part 9 building, structural members may be designed using applicable Part 9 provisions, recognized good engineering practice, or Part 4 where permitted or required by the Code.

Part 4 considers gravity, snow, wind, earthquake, and other effects. BCBC 2024 references standards including CSA O86:19 for wood, CSA S16:19 for steel, CSA A23.3:19 for concrete, and CSA S304-14 for masonry. Buildings outside the scope of Part 9 generally require professional structural design under Part 4.

Part 9 Buildings With Part 4 Structural Components

A Part 9 building can contain individual components that fall outside Part 9. The BC Guide to the Letters of Assurance identifies examples that may require Part 4 structural design:

• Beams carrying point or concentrated loads

• Girder trusses

• Trusses spanning more than 12.2 m

• Proprietary engineered structural components

• Members exceeding applicable Part 9 limits

An open-concept renovation in Surrey or custom home in Kelowna may introduce concentrated reactions or unusual framing that cannot be selected from Part 9 tables.

Structural Engineering Triggers in Part 9 Projects

Professional structural design may be required when proposed work cannot be fully addressed by Part 9 provisions or when the Code specifically requires Part 4 design.

Common triggers include:

• Long or heavily loaded beams

• Large structural openings

• Non-standard wall or roof framing

• Complex load paths

• Alterations affecting existing supports

• Foundation conditions outside Part 9 limits

• Lateral bracing conditions requiring engineered design

BCBC 2024 includes updated Part 9 lateral bracing requirements for wind and earthquake. Depending on the building configuration and site-specific conditions, engineered lateral design or Part 4 design may be required.

At Parsways Inc., reviewing the architectural scope early helps identify which components remain prescriptive and which require engineered design.

Schedule B for Engineered Part 9 Components

BCBC 2024 Division C requires professional design and Letters of Assurance for structural components in Part 9 buildings when those components fall outside Part 9. The structural Registered Professional of Record provides the applicable Schedule B and field review for that scope.

Where multiple Part 4 components or disciplines are involved, additional coordination may be required. Permit requirements should be coordinated with the local authority.

Local Permit Requirements Across BC

Local authorities administer the permit process, so submission requirements can differ across BC. Projects in Burnaby, Surrey, and Victoria may require sealed structural drawings and professional assurance where engineered components are involved.

The key issue is not simply whether the building is Part 9, but whether the proposed structural work remains within Part 9 provisions.

Conclusion

BC Building Code Part 9 provides prescriptive solutions for many small buildings, but Part 9 classification does not eliminate structural engineering requirements. When a structural component exceeds Part 9 limits, Part 4 design and professional involvement may be required.

At Parsways Inc., we provide structural engineering for Part 9 projects across British Columbia, including engineered beams, structural openings, framing modifications, foundations, and other components requiring Part 4 design, coordinated with BCBC 2024 and applicable permit requirements.