Specialty Structural Engineering Services for Ontario Properties

What Is Specialty Structural Engineering?

Specialty structural engineering addresses structural problems that fall outside the scope of standard building frame design — specific components, systems, or conditions requiring focused expertise and design methodologies. While the structural engineer of record designs the primary building structure (foundations, floors, columns, lateral system), many projects require additional specialized structural analysis for individual components or unique loading conditions.

Common specialty structural engineering needs in Ontario include: rooftop mechanical equipment support (dunnage framing); parapet and penthouse/bulkhead structures; post-installed anchorage to concrete and masonry; formwork engineering under OHSA 213/91; gravity and lateral connections for mass timber (CLT/Glulam) structures; curtain wall anchorage; and structural assessment for solar array installation. Each of these requires a P.Eng. with specific technical expertise and awareness of the applicable Ontario regulatory and code requirements.

Roof Dunnage & Equipment Structures

Rooftop equipment installation is one of the most common specialty structural requests in Ontario — HVAC replacements, cooling tower upgrades, generator additions, and new solar arrays all require structural assessment and, in most cases, a sealed structural design for the support system.

Why Rooftop Structures Are Technically Demanding

Roof dunnage design involves multiple interacting structural challenges not present in interior floor design:

• Load concentration: Mechanical equipment creates concentrated loads at specific points rather than distributed floor loads. Roof structures typically designed for 1.0–2.5 kPa live load may not sustain the concentrated reactions from large equipment without local reinforcement.
• Wind uplift at elevation: NBCC 2020 wind load pressure coefficients for equipment on roofs are significantly higher than for equipment at ground level, due to both increased wind speed at elevation and geometric effects. Large exhaust fans or cooling towers with significant exposed area can generate substantial overturning moments that must be resisted at the anchorage.
• Vibration: Rotating equipment (compressors, fans, pumps) generates mechanical vibration that must be isolated from the building structure using vibration isolators — but the isolators must be structurally designed to resist both gravity and seismic/wind loads without allowing equipment movement.
• Seismic anchorage: Under NBCC 2020 seismic provisions, rooftop equipment must be anchored to resist seismic forces — particularly important in Toronto, where the design spectral acceleration (Sa(0.2)) is approximately 0.28–0.32g.
• Roof membrane penetration: Every structural attachment to an existing roof penetrates the waterproofing system, creating a water infiltration risk. The structural design must be coordinated with the roofing consultant to ensure attachments are properly flashed and sealed.

Dunnage Frame Types

Structural steel dunnage frames are typically custom-designed for each project. Common configurations include: perimeter frames spanning between structural roof members (minimizing penetrations); welded or bolted rigid frames where equipment width constraints require cantilevered outriggers; bridging frames that span multiple roof zones to avoid concentrated loads on roof deck cantilevers; and integrated equipment platforms with stair/ladder access systems.

Parapet, Bulkhead & Rooftop Structures

Parapet Structural Issues

Parapets — the upward wall extensions above the roofline — are a significant source of structural vulnerability in Ontario's existing building stock. Pre-1970s masonry parapets are particularly at risk because they predate modern OBC wind and seismic requirements and were typically unreinforced. NBCC 2020 appendix wind pressure coefficients at the roof-parapet interface are 1.5–2.0× the values used for the main building surfaces, creating high out-of-plane demands on parapets.

Toronto's Supplementary Standard SB-10 (seismic design) requires that unreinforced masonry parapets on buildings undergoing substantial alterations be assessed and, if found inadequate, retrofitted. Parapet retrofits typically involve reinforcing the masonry with epoxy-grouted rebar, installing structural steel pipe or tube knee-brace systems anchored to the roof structure, or rebuilding the parapet in reinforced masonry or lightweight metal coping systems.

Rooftop Bulkheads & Penthouse Structures

Elevator machine rooms, stair bulkheads, and mechanical penthouses are small rooftop structures that require structural design for both gravity and lateral (wind + seismic) loads. Because they project above the main roofline, wind loads are amplified relative to the main building. Seismic demands in Toronto require the structure to be designed as an SFRS (Seismic Force Resisting System) with defined Rd and Ro values. Masonry penthouses on pre-1970s buildings are a common flag in building condition assessments.

Anchorage Engineering

Post-installed anchors — anchors or bolts installed into existing concrete or masonry after the original construction — are governed by OBC Part 4 and specifically by CSA A23.3 Annex D (for concrete anchors) and CSA S304 (for masonry anchors). Anchorage design for structural connections requires a P.Eng. and sealed drawings in Ontario.

Anchor Types and Applications

• Mechanical expansion anchors: Torque-controlled or displacement-controlled. Used for light-duty framing connections, equipment vibration isolator bases, mechanical pipe supports.
• Chemical adhesive anchors: Epoxy or hybrid adhesive systems providing higher load capacity, suitable for tension-dominated connections where concrete edge conditions exist. Used for structural connections, railing post bases, retrofit shear key installations, and heavy equipment mounts.
• Undercut anchors: High-performance system with positive interlock in concrete. Used for curtain wall connections, fall protection anchor points, and safety-critical structural connections where mechanical lock is required.
• Cast-in-place headed bolts: Designed per CSA A23.3 Part D. Used in new construction for column base plates, equipment pads, and hold-down anchors.

Safety-Critical Anchorage

Fall protection anchor points installed on Ontario rooftops and facades must comply with OHSA and CSA Z259.15 (anchorage systems) and CSA Z259.16 (design of active fall protection systems). A structural engineer must design and seal the anchorage — anchors rated for 22.2 kN minimum single anchor capacity. This is distinct from, and in addition to, the general anchorage design for equipment or railing loads.

Formwork Engineering in Ontario

Formwork is the temporary system of forms, shoring, and falsework that supports fresh concrete until it achieves sufficient strength to support itself. In Ontario, formwork engineering is regulated by both the OBC (for structural adequacy) and OHSA Regulation 213/91 (Construction Projects) for worker safety.

OHSA 213/91 Section 85 — When You Need a P.Eng.

OHSA 213/91 Section 85 requires that formwork and shoring for slabs, beams, and columns where the concrete load exceeds 4.5 kN per linear metre of form must be designed and sealed by a professional engineer. In practice, this threshold is reached by any slab greater than approximately 100mm thick over a standard bay — meaning virtually all suspended concrete floor and roof form systems require a P.Eng. sealed formwork design on Ontario construction sites.

Formwork Design Elements

A P.Eng. sealed formwork design for an Ontario cast-in-place project typically includes: shoring layout plan showing shore spacing, type, and capacity; shore design calculations confirming capacity under wet concrete loads (fresh concrete pressure on vertical forms; distributed load on shores during placement); re-shoring plan for multi-storey construction (to distribute loads from upper floors to supporting levels during construction); and stripping sequence with minimum concrete strength requirements per CSA A23.1 (standard: 70% of 28-day strength before removal of supporting forms for slabs, confirmed by cylinder testing or maturity monitoring).

Mass Timber Connections

Mass timber construction — using Cross-Laminated Timber (CLT), Glulam, Nail-Laminated Timber (NLT), or Laminated Strand Lumber (LSL) for structural elements — is growing rapidly in Ontario, driven by provincial policy changes (2020 OBC amendment allowing mass timber to 12 storeys), sustainability goals, and developer demand for exposed wood interiors. Structural connections in mass timber require specialized engineering not covered in traditional steel or concrete engineering practice.

Connection Types in Mass Timber

• Self-tapping screws (STS): The workhorse of CLT connections — fully threaded screws installed at various angles to create withdrawal, shear, or combined-action connections at panel-to-panel, panel-to-beam, and panel-to-wall interfaces. Designed per CSA O86 Annex A (mass timber provisions) and manufacturer-specific design tables (SWG Assy, Spax, Rothoblaas).
• Concealed metal plates with slotted-in connectors: High-capacity joist hanger-type connections for beam-to-column moment or gravity connections — commonly used for Glulam beam connections to CLT walls or concrete cores.
• Steel knife-plate connections: Steel plates biscuit-inserted into CNC-routed slots in timber members, connected by bolts, lag screws, or STS. Common for timber-to-concrete connections and column base details.
• Timber-to-concrete interface connections: Common in hybrid structures where CLT floor panels are supported on concrete shear walls or steel frames. Require careful detailing for fire (OBC Table 9.23.12.1 for protected assemblies), acoustic isolation (OBC STC/OITC requirements for residential), and moisture management at the interface.

CSA O86 & Ontario Requirements

Mass timber structural design in Ontario is governed by CSA O86-19 (Engineering Design in Wood) and the OBC 2012 with 2020 mass timber amendments. The 2020 OBC amendments allow mass timber buildings up to 12 storeys with specific encapsulation requirements and revised exit/occupancy classifications. Engineers designing mass timber systems in Ontario must be familiar with both the structural standards (O86) and the OBC fire provisions — these interact in ways that require both building code and structural expertise.