When does OHSA Reg 213/91 require an engineer-designed temporary works plan?

Ontario Regulation 213/91 requires engineer-designed temporary works whenever the formwork, shoring, falsework, cofferdam, excavation support, or rigging condition depends on project-specific engineering rather than a simple standard detail. The engineer's design must be available on site during construction.

What is the difference between formwork and falsework in Ontario?

Formwork refers to the molds or forms into which fresh concrete is cast — the contact surfaces. Falsework refers to the temporary structural system that supports formwork and the wet concrete loads before the concrete gains sufficient strength to self-support. Both require engineering whenever the loading or geometry goes beyond a simple standard condition under OHSA Reg 213/91.

Temporary Works Engineering in Ontario: OHSA Reg 213/91, Formwork & Shoring

Q: What are the engineer's ongoing responsibilities during temporary works construction?

Under PEO's Guidelines for Professional Engineers in Ontario, the temporary works engineer has ongoing responsibilities including: providing a written design with load assumptions clearly stated; specifying inspection requirements before concrete placement; requiring the contractor to notify the engineer when the formwork is loaded; and being available for site consultation. The PEO Practice Bulletin on Temporary Works notes that significant design deviations during construction must be reviewed and re-sealed by the engineer before the modified system is loaded.

Q: What temporary support is required when excavating near existing buildings in Ontario?

Excavation near existing buildings requires a project-specific engineer's assessment whenever the work could affect adjacent foundations or structures. The resulting support plan may include shoring, underpinning, monitoring, or staged excavation measures depending on the site constraints and the current regulation.

Temporary Works| 7 min read|April 2026 · By Asvakas Engineering

What Are Temporary Works?

Temporary works are engineered structures required during construction that are not part of the permanent building. They include: formwork and falsework for concrete construction; shoring and bracing for excavation and existing structures; cofferdams for below-grade water control; scaffolding for access and facade work; and propping systems to support existing floors and walls during alteration. Unlike permanent structures, temporary works are typically removed upon substantial completion of the associated permanent construction.

OHSA Reg 213/91 Requirements

Ontario Regulation 213/91 (Construction Projects) under the Occupational Health and Safety Act is the primary regulatory framework for temporary works. Key provisions:

Situation	OHSA Reg 213/91 Requirement
Formwork or falsework outside simple standard layouts	P.Eng. design required; engineer-sealed drawings on site
Excavation support where soil, geometry, or adjacent conditions create risk	P.Eng. design or site-specific engineering assessment required
Temporary works affecting nearby structures or utilities	Engineering review, monitoring, and staged construction requirements are typically needed
Falsework for bridges and elevated structures	P.Eng. design always required
Cofferdams and water-control support systems	P.Eng. design always required
Special lifting or suspended support systems	Engineered rigging/support design required

In all engineer-required cases, the design drawings must be on site, the contractor must notify the engineer before loading, and the engineer must confirm the constructed system conforms to the design before concrete placement or excavation commences.

Types of Temporary Works

Formwork & Falsework

Freshly cast concrete applies significant hydrostatic and dynamic loads. Concrete density of approximately 2,400 kg/m³ plus construction live loads and lateral concrete pressure must be resisted by the formwork system. CSA S269.1 (Falsework and Formwork) provides design guidance. High-lift concrete placements, self-consolidating concrete (SCC), and large-pour mats create elevated pressures — all require careful engineering.

Excavation Shoring

Toronto's subsurface conditions range from competent shale and limestone (Dundas/Queen Street level) to soft lakebed clay and fill (lakefront and older industrial lands). Excavation support systems must be designed for actual site soil conditions. Common systems: soldier pile and lagging, sheet pile, secant pile walls, soil nails, and ground anchors. Monitoring programs are required when excavating near sensitive structures.

Propping & Temporary Structural Support

During alterations to existing buildings, temporary propping may be required to support floor/wall loads while permanent structure is removed or modified. Propping systems must be designed for load redistribution paths and may require sequential loading analysis.

Engineering Design Requirements

A compliant OHSA Reg 213/91 temporary works design package includes:

Design calculations sealed by a P.Eng. (PEO licensed)
Construction drawings showing member sizes, spacing, connections, and bracing
Stated load assumptions and sequence of operations
Pre-loading inspection checklist
Required monitoring and inspection protocol
Written notification requirement to engineer before loading

⚠️

OHSA enforcement in Ontario is active. The Ministry of Labour (MLITSD) inspectors regularly review construction sites and can issue stop-work orders for temporary works constructed without required engineering. OHSA penalties and liability exposure can be significant, so project teams should confirm the current enforcement framework rather than rely on outdated fine amounts.

Excavation Near Existing Buildings

OHSA Reg 213/91 requires a P.Eng. assessment before excavation that could affect adjacent foundations or structures. Toronto's dense urban fabric — often involving excavation immediately adjacent to heritage buildings, operating transit infrastructure, and shared foundation walls — requires sophisticated geotechnical-structural interaction analysis. Key tasks: settlement analysis, pile load monitoring, vibration monitoring, trigger/action levels, and contingency plans.

Frequently Asked Questions

When does OHSA Reg 213/91 require P.Eng.-designed temporary works?

OHSA requires P.Eng.-designed temporary works whenever the configuration depends on project-specific engineering, including non-standard formwork, excavation support, falsework, cofferdams, and other temporary systems that cannot rely on a simple standard detail or manufacturer table.

What is the difference between formwork and falsework?

Formwork is the concrete contact surface or molding system. Falsework is the temporary structural system supporting the formwork against wet concrete loads. Both require engineering whenever the actual loading, geometry, or construction sequence goes beyond a simple standard condition.

What are the engineer's ongoing responsibilities during temporary works?

Under PEO guidelines, the engineer must provide sealed drawings, specify inspection requirements before loading, and be available for site consultation. Significant deviations from the design must be reviewed and re-sealed before loading the modified system.

What temporary support is required when excavating near existing buildings?

Excavation near existing buildings typically requires a P.Eng. assessment and a project-specific shoring or underpinning plan whenever the work could affect adjacent support conditions. Vibration monitoring and settlement monitoring of adjacent structures are standard Toronto practice.

Temporary Works Engineering Across Ontario

Asvakas Engineering provides OHSA Reg 213/91 compliant designs for formwork, shoring, falsework, and excavation support across Ontario construction projects.

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