Structural Openings in Ontario Buildings: Windows, Doors & Passage Cuts

OBC Framework: Part 9 vs. Part 3 Buildings

The Ontario Building Code governs structural requirements for new openings based on building classification:

• OBC Part 9 (Housing and Small Buildings): Applies to houses, duplexes, and small buildings not exceeding 3 storeys and 600 m² in building area. Part 9 Section 9.23 provides prescriptive lintel span tables for wood and steel lintels over door and window openings in wood-frame construction. These prescriptive solutions eliminate the need for a P.Eng in straightforward Part 9 residential scenarios — but only when all conditions of the table (load, span, tributary width) are satisfied.
• OBC Part 3 (Large Buildings): Applies to buildings exceeding Part 9 limits. All structural elements must be designed per OBC Part 4 requirements and applicable CSA standards (CSA S16 for steel; CSA A23.3 for concrete; CSA O86 for wood). P.Eng design and General Review are mandatory.
• Part 11 (Renovation) applies to alterations in all building types: Structural elements being altered in existing buildings must comply with current OBC Part 4 or Part 9 requirements for those specific elements.

For masonry buildings — whether Part 9 or Part 3 — prescriptive OBC tables do not apply to masonry lintels, which must always be designed by a P.Eng consistent with CSA S304 (masonry) or by a steel beam design per CSA S16.

Identifying Load-Bearing Walls in Ontario Buildings

Before cutting any opening, the structural system must be understood. In Ontario buildings:

• Wood-frame houses: Exterior walls are almost always load-bearing; interior walls parallel to joists are usually non-bearing; walls perpendicular to floor joists are typically bearing walls
• Masonry buildings: All solid masonry walls (brick, concrete block, stone) are load-bearing unless engineering documentation shows otherwise
• Concrete frame buildings: Floor slabs span between beams, frames, or walls; interior concrete walls may carry significant shear loads even if they appear not to be in the direct gravity load path
• Steel frame buildings: Non-structural masonry infill panels are common; the steel frame carries all gravity and lateral loads — but infill panels may provide lateral bracing that cannot be casually removed

When in doubt, engage a structural engineer to confirm load-bearing status before issuing a permit drawing or starting construction.

Lintel and Header Beam Design Under OBC

The lintel or header beam spanning a new opening must be designed for the tributary loads above. OBC requirements for Part 3 buildings:

• Gravity loads per OBC Table 4.1.5.3 (floor live loads, roof snow load, self-weight)
• Lateral wind uplift on lintels in exterior wall positions
• Beam sized per CSA S16 (steel) or CSA O86 (engineered wood) with appropriate load combinations per NBC 2020 / OBC
• Bearing at each end must be checked: block or stud bearing capacity, bearing plate design where required
• Deflection limits: L/360 under live load, L/240 under total load per OBC

Common steel beam sizes used for Ontario residential lintel applications: HSS or W-shape beams in W8, W10, W12 range, depending on span and load. For most residential Part 9 openings, LVL (Laminated Veneer Lumber) beams are cost-effective and practical — sized per manufacturer's tables or P.Eng calculation.

Temporary Shoring Requirements

Temporary shoring must be installed before any load-bearing wall material is removed. For Ontario projects:

• The P.Eng designs the shoring scheme showing shore locations, size, and capacity
• Shoring must be sized to carry all loads (floor, snow, self-weight) from the structure above the proposed opening
• Under Ontario Regulation 213/91 (Construction Projects), the employer must ensure temporary supports are adequate — this obligation aligns with the P.Eng's shoring design
• The shoring sequence is part of the construction methodology: install shores → cut opening → install lintel with full bearing → remove shores

Masonry Wall Openings

Ontario's urban building stock includes substantial masonry construction from the 1880s through the 1960s. Creating openings in masonry walls requires:

• P.Eng investigation to determine the masonry type (solid brick, hollow block, stone), condition, and structural role
• Steel lintel design per CSA S16 for the new spanning element — typically a wide-flange beam or double steel angles
• Staged cutting sequence using diamond blade saws to minimize vibration and prevent uncontrolled crack propagation
• Bearing plates at lintel ends to distribute concentrated load into the masonry without causing local crushing
• In heritage buildings, coordination with the local heritage planner if the building is designated under the Ontario Heritage Act

Building Permit Process & P.Eng General Review

Creating a new opening in a load-bearing wall in Ontario requires a building permit under the Building Code Act, 1992:

• Permit application documents: P.Eng-stamped structural drawings showing existing wall condition, proposed opening, new lintel/beam with section and connection details, and temporary shoring plan; structural calculations prepared or reviewed by a P.Eng
• P.Eng General Review: For Part 3 buildings, the engineer of record must commit to General Review under O.Reg 332/12 and file commitment and final review reports with the CBO. For Part 9 buildings, General Review is not mandatory under OBC but may be required by the CBO in particular cases.
• Inspection schedule: The CBO will conduct building inspections at prescribed stages; the P.Eng's site review visits must coincide with critical construction stages (shoring installation, lintel placement, load transfer)
• Final inspection and occupancy: After all work is inspected and the P.Eng files the final General Review report, the CBO closes the permit