Do I Need a Structural Engineer? A BC Homeowner's Guide

You need a structural engineer in British Columbia whenever your project takes the structure outside what the prescriptive housing provisions of the BC Building Code cover, or whenever your municipality asks for sealed drawings or letters of assurance. That covers new builds and additions, removing a load-bearing wall, adding a storey, foundation and excavation work, retaining walls that support a building, and most changes of use. Paint, flooring, cabinets and non-structural partitions almost never need one.

If the load path changes anywhere between the roof and the soil, you need a structural engineer. Part 9 of the BC Building Code covers buildings three storeys or fewer with a building area of 600 square metres or less. Step outside its span tables and the design becomes Part 4 work for a registered professional. Only a registrant of Engineers and Geoscientists BC can seal drawings and sign a Schedule B. Requirements differ by municipality, and Vancouver applies its own building by-law rather than the provincial code.

When do I need a structural engineer? The triggers that matter in BC

Where Part 9 ends and Part 4 begins

Part 9 of the BC Building Code 2024, in force province-wide since 8 March 2024, covers housing and small buildings: three storeys or fewer in building height, with a building area not exceeding 600 square metres, in residential, business, mercantile, or medium- and low-hazard industrial occupancies. Building area is the greatest horizontal area above grade within the outside surface of the exterior walls, so it is the footprint, not every storey added up.

Inside those limits, Part 9 gives prescriptive span and framing tables a designer can follow without an engineer. Step outside them and the work becomes Part 4 structural design, carried out and sealed by a registered professional.

The province's Guide to the Letters of Assurance is direct about where that line falls inside a house. Uniformly loaded steel and glulam beams sized straight from the Part 9 span tables do not require letters of assurance. Beams with concentrated or non-uniform loads do, as do girder trusses, long-span trusses and proprietary engineered products. Where a Part 9 house carries several such components, many authorities having jurisdiction ask that the engineer's Schedule B cover integrated structural design and field review for the whole building.

Removing or altering a load-bearing wall

This is the most common reason a homeowner calls, and the clearest example of the Part 9 boundary. Whether a wall carries load is rarely obvious from inside the room: joist direction, what sits above, and whether the wall forms part of the lateral system all matter. The beam replacing it almost always picks up point loads from posts, girder trusses or an upper-floor bearing wall, and a beam with concentrated loads sits in Part 4 however modest the house. Our guide to removing a load-bearing wall in Vancouver walks through the sequence.

Additions, added storeys and attic conversions

Additions raise a question beyond the new framing: can the existing structure take the load? They often land on footings sized decades ago for a smaller building, so the review runs to the soil. Adding height also increases the seismic and wind forces the building must resist, and that matters more than it used to: the National Building Code of Canada 2020 adopted Canada's sixth-generation seismic hazard model, which raised modelled demands at many Lower Mainland sites.

Foundations, excavation and ground conditions

Ground is where Metro Vancouver stops being generic. Provincial letters of assurance guidance treats a Part 9 site as needing a subsurface investigation by a registered professional once conditions fall outside Part 9: allowable bearing pressure below 75 kilopascals, slope instability, shoring, underpinning, deep foundations, or retaining walls critical to the building's foundations.

Those triggers map onto local geography. The Fraser delta silts, sands and peat under Richmond, Delta and parts of south Surrey and south Vancouver are soft and potentially liquefiable. Where peat or fill is present, delta municipalities commonly require a geotechnical soils report before a foundation is designed, and an engineered foundation may follow even on a small house. The glacial tills under Burnaby, New Westminster and the North Shore benches are far stiffer, but the North Shore trades that advantage for slope, and municipalities there commonly designate steep ground as a hazard development permit area with geotechnical requirements of its own.

Telling shrinkage cracking from active settlement is foundation engineering work, not a contractor's call.

Decks, retaining walls and site structures

A ground-level deck on sleepers is usually carpentry; an elevated deck, balcony or carport is structural, because guards, snow load and connection detailing govern. Snow load is not one number here either: a roof in Whistler, Squamish or high on the North Shore slopes carries a far heavier design load than the same roof at sea level in Vancouver.

Retaining walls split in two. A wall critical to supporting a building's foundations is a structural element of the building. A site wall holding back nothing but ground is not regulated by the Building Code at all, which is why municipal rules vary so widely. Our piece on when a retaining wall in BC needs an engineer covers the triggers.

Suites, extra units, change of use and seismic upgrades

A secondary suite or laneway house usually means new openings, stairs, fire separations and sometimes a new foundation, which is why most need sealed drawings. Since Bill 44 in 2023, most BC municipalities must permit three to four residential units on lots previously zoned single-family or duplex, and up to six within 400 metres of a frequent transit stop.

A change of use is a bigger trigger than owners expect. Converting a house to a daycare, or a warehouse bay to a gym, raises occupancy loads and forces a wider code review. In Vancouver, the by-law also requires seismic upgrading of many existing buildings at a major renovation or change of use, generally to at least 75 per cent of current-code seismic force levels, with relaxations for the unreinforced masonry common in Gastown and Chinatown. That is seismic engineering work.

Do I need a structural engineer for this project?

Treat this as a starting point; your authority having jurisdiction decides what it accepts.

Engineer, architect, designer or inspector: who does what

A structural engineer is a registrant of Engineers and Geoscientists BC. They design and seal the load-carrying elements, sign the structural letters of assurance, and carry out field reviews. Their firm also needs a permit to practice, whose number must appear on authenticated documents. EGBC bylaws require a documented independent review of structural designs, so a second engineer checks the work before it is issued.

An architect is regulated separately and is responsible for the building as a whole. A building designer prepares permit drawings for smaller residential projects; good ones are useful, but they are not registered professionals, so they cannot seal drawings or sign a Schedule B. A municipal building inspector works for the city, not for you, and a verbal comment from one is no substitute for a sealed drawing. A geotechnical engineer deals with the ground, and on soft delta soils their report precedes the structural design.

What BC municipalities actually ask for

"Sealed" means signed, sealed and dated by a registered professional. BC then layers on its letters of assurance: Schedule A, Confirmation of Commitment by Owner and Coordinating Registered Professional; Schedule B, Assurance of Professional Design and Commitment for Field Review; Schedule C-A, Assurance of Coordination of Professional Field Review; and Schedule C-B, Assurance of Professional Field Review and Compliance. Our guide to Schedules B and C explains when each is submitted.

That guide is clear that letters of assurance are not generally intended for Part 9 buildings, though authorities having jurisdiction often elect to use them, and that only Part 9 components falling within Part 4 must be covered. In practice:

• Permit checklists differ. Some building departments want sealed structural drawings with a stated basis of design, Schedule B letters from the structural, geotechnical and envelope professionals, and confirmation of professional liability insurance; others ask for far less on the same scope.
• Several municipalities require a designated structural engineer to be engineer of record for the primary structural system of a Part 3 building, and set out where that requirement stops.
• On the delta, peat or fill on a property commonly triggers a geotechnical soils report before a foundation can be designed.
• On the North Shore and other sloping ground, hazard development permit areas can add geotechnical requirements to an otherwise ordinary house.
• In Vancouver, the city applies its own Vancouver Building By-law 2025 rather than the provincial code, with a transition period for in-stream projects, covered in our note on the Vancouver Building By-law 2025 changes.

Surrey, the Tri-Cities and the Fraser Valley municipalities keep their own checklists too. Confirm the specifics with your building department rather than assuming a neighbouring city's rules apply.

What a structural engineer actually delivers

• A review of existing conditions, usually including a site visit, before design starts.
• Calculations for gravity, snow, wind and seismic loads using the Canadian standards that apply: CSA O86 for wood, CSA S16 for steel, CSA A23.3 for concrete, CSA S304 for masonry, CSA S136 for cold-formed steel.
• Sealed structural drawings with framing plans, member sizes, connection details and specifications.
• Letters of assurance where required: Schedule B at permit stage, Schedule C-B before occupancy.
• Field reviews during construction, or a standalone review letter for an insurer, lender or strata where no design is required.

Common mistakes that cost time

Demolishing first and asking afterwards is the expensive one: once framing is open and shoring improvised, the engineer is solving a harder problem under pressure. Assuming a thin wall cannot be structural is another, as is bringing the engineer in after the drawings are frozen. And do not skip field reviews: an engineer cannot sign a Schedule C-B for work they never saw.

What to have ready before you call

Have the civic address and municipality, a plain description of the work, any drawings or survey you hold, photos of the area, and the approximate age and construction type of the building. Say whether a permit application is open and whether a contractor is booked. Those details let an engineer scope the work honestly.

Working with MAF Engineering

MAF Engineering Ltd. is a consulting structural, seismic and civil engineering firm serving Greater Vancouver, the Fraser Valley, Sea-to-Sky and Vancouver Island. Our principal, Mir Afshar Niakouei, P.Eng., has more than 25 years of experience, is registered in British Columbia, Alberta and Ontario, and is a member of EGBC and SEABC. We work on everything from single-wall removals to multiplexes, and we will say so if you do not need us.

If you are not sure whether your project needs sealed drawings, call 778.840.9867 or get in touch with a short description and a few photos. We will tell you what your municipality is likely to want.