A mono stringer stair looks simple from the room. The engineering behind it resolves bending in two directions simultaneously — vertical load from the treads and horizontal load from the guard — through a single beam with two anchor points. Getting that right is what makes the stair safe, inspectable, and approvable under the BC Building Code.
Does a mono stringer stair need an engineer in BC?
Most feature mono stringer stairs in Metro Vancouver require at least informal engineering coordination, and the majority require a sealed (stamped) Schedule B engineer's letter for the building permit. The BC Building Code requires a Letter of Assurance (Schedule B) from a Registered Professional for any structural design that is not covered by prescriptive tables in Part 9. A feature mono stringer stair — with a central HSS beam, cantilevered treads, and a glass or cable guard — is virtually always outside the prescriptive scope. Part 3 buildings (commercial, multi-family) always require a Designated Structural Engineer to seal structural drawings. Confirm requirements with your local authority having jurisdiction (AHJ).
- Part 9 residential: Schedule B likely required for the stair structure.
- Part 3 commercial / multi-family: Designated Structural Engineer required.
- City of Vancouver: VBBL follows the same framework; confirm with the building department.
- Source: Engineers and Geoscientists BC; BC Building Code 2018, Division C, Part 2.
What the engineer reviews on a mono stringer
The engineer of record (or the stair's own consulting engineer) reviews five structural elements: the beam itself (section, wall thickness, span, and deflection under live and dead load); the tread bracket connections (weld detail, load path, and weld quality — CWB certification matters here); the lower base plate anchor (bolt size, embedment, and concrete or wood substrate); the upper cap plate anchor (structural rim joist, steel header, or concrete deck); and the guard attachment (lateral load from the guard transfers to the tread and then to the bracket — not just a finish detail).
Tread loads and the code live load requirement
The BC Building Code sets minimum live load requirements for stairs. For residential stairs serving a single dwelling unit, the tread live load is lower than for egress stairs in commercial occupancies. The engineer sizes the beam, brackets, and connections to the applicable live load plus a code-prescribed concentrated load at the stair guard. Over-designing to meet commercial loads on a residential stair is sometimes done to create a safety margin, but it adds steel weight — confirm the applicable load case with the engineer.
Beam sizing: what changes the section
For most residential mono stringers in Metro Vancouver, an HSS 8×3 (203×76 mm) or HSS 10×3 (254×76 mm) in 3/16" or 1/4" wall thickness covers the common span and load range. A longer span (more than 14–16 steps), a heavier tread material (stone or concrete-look), or a curved beam all require the engineer to recalculate the section. Do not assume the same beam that worked on one project will work on another.
Coordinating engineering with the project schedule
Engineering needs to happen before fabrication, not after. The shop drawing set — which shows the beam, the bracket details, the anchor points, and the weld specifications — is typically prepared by the fabricator and reviewed by the engineer. On projects with an engineer of record for the whole building, the stair engineer's review should be coordinated with the overall structural set so the anchor details appear in both drawings.
Related questions
Who provides sealed engineering for a mono stringer stair?
Some projects have an engineer of record who reviews the stair as part of the overall structural package. On projects without a structural engineer of record, we work with the client or the GC to engage a consulting structural engineer who specializes in custom stairs in BC. We can help define the information the engineer needs to review the stair scope.
What is a Schedule B letter and when is it required?
A Schedule B (Letter of Assurance from a Registered Professional) is a signed document from a licensed engineer stating that the structural design meets the requirements of the BC Building Code. It is required for structural elements that fall outside the prescriptive Part 9 tables — which includes virtually all feature mono stringer stairs. The building department requires it before a building permit is issued for the stair scope.
Does CWB certification affect the engineering requirement?
Yes. CWB (Canadian Welding Bureau) certification under CSA W47.1 means the shop's welding procedures and welders are audited to a national standard. Engineers designing structural steel connections specify that weld quality meets CSA W47.1, and CWB certification is the documentation that proves it. Without CWB certification, the engineer cannot rely on the fabricator's weld quality in the structural calculation.
How much does mono stringer engineering cost?
Engineering fees for a residential mono stringer stair in Metro Vancouver vary by scope and engineering firm. Most feature stair reviews run in the range of $1,500–$4,500 depending on complexity, drawings required, and review rounds. That fee is a small fraction of the total stair cost and is not optional for a permitted structural stair.
Discuss mono stringer engineering guide for a real project
Send drawings, photos, or a rough scope and we will help define the practical next step.