Friday afternoon, demolition Monday
A general contractor calls the structural engineer of record at 3:40 PM on a Friday. The crew is pulling down an interior partition between two tenant units on Monday morning, and the original drawings show a header carrying joists above the wall in question. The GC's shoring sub has emailed a proposed temporary support arrangement. The engineer has ninety minutes to decide whether it is acceptable, issue a sealed letter the sub can give to the crew foreman, and get back to the rest of the day's work.
The letter goes out at 5:11 PM. It is a page and a half on firm letterhead, addressed to the GC by name, referencing the project number and the drawing sheet the header appears on. It names the element being removed, identifies the load path during the work, states that the proposed shoring is acceptable under the engineer's stated assumptions, and closes with a limitations paragraph that takes nearly a quarter of its length.
Seventy-two hours later the partition is out, the shoring is holding, and nobody remembers the letter. It sits in the project file as the single load-bearing artifact documenting the engineer's professional opinion about a temporary condition that no longer exists. If anything goes wrong in that period, or in the years of residual liability after, the letter is the record of what the engineer knew, assumed, and committed the firm's seal to.
What the letter actually does
A shoring requirement letter is a specific shape within the broader sealed opinion letter category. Its defining features:
It is contractor-facing. The recipient is the GC or the demolition sub, not the owner, not the architect, not the municipality. The letter's tone assumes a trade reader, and its scope statements are written so a foreman can act on them.
It names what is being removed. The letter identifies the specific structural or semi-structural elements whose load paths the shoring has to carry during the work. "An interior load-bearing wall between grid lines B3 and B5 supporting a 200 mm by 400 mm lintel above a 3.2 m opening" is a scope statement. "The wall indicated" is not.
It identifies the loads the shoring must carry. Derived from the governing drawings, the gravity load the removed element was supporting, and any applicable dynamic or incidental loads during the work. The letter does not reproduce the calc, but it names the value the shoring is being asked to support, usually in factored or service terms with units stated.
It either endorses the contractor's proposed shoring or defines what the engineer requires. This is the most consequential sentence in the document, and the point where the language has to be exact. The letter either says "the proposed arrangement is acceptable under the stated assumptions" or "the following shoring arrangement is required before removal proceeds." The two sentences commit the firm to different professional postures.
A shoring requirement letter is not a shoring design. On projects where a shoring engineer is engaged, the full design of temporary works, including member sizes, connections, bracing, and means-and-methods, sits with the contractor's own engineer; on smaller interior demolition work the engineer of record sometimes specifies the shoring directly. Either way, the letter reviews an arrangement against the requirements of the permanent structure it touches. Conflating review with design produces a letter that either over-commits the engineer to the contractor's means-and-methods or under-commits the contractor to safe execution.
The five load-bearing sections
A defensible shoring requirement letter has a recognizable body. The section names vary by firm, but the five sections below show up in every shoring letter that holds up under review.
1. DOCUMENTS REVIEWED. Names every drawing, specification, and submission the engineer used to form the opinion. Drawing numbers with revision numbers and dates. The contractor's proposed shoring submission with its own date and revision. Any prior field review reports, prior letters, or prior dispute correspondence that touches the same element. Strong language: "S-201 rev 3, dated 2022-04-17; the contractor's shoring submission ref SH-001 dated 2026-04-21." Weak language: "the original structural drawings and the contractor's shoring proposal."
2. EXISTING STRUCTURE. Describes the element to be disturbed in enough detail that a reviewer years later could identify which element the letter is about. Material, dimensions, connection type, governing load per the original design. Strong language: "The wall in question is a 190 mm masonry load-bearing wall, grouted at all cells, supporting a 200 mm by 400 mm reinforced concrete lintel over a 3.2 m opening per S-201 detail 7." Weak language: "the existing load-bearing wall."
3. PROPOSED WORK AND SHORING METHODOLOGY. Summarizes the scope of the demolition and describes the shoring arrangement being evaluated. The methodology is reproduced in enough detail that the letter stands on its own without reference to the contractor's submission. Strong language: "Two HSS 89 by 89 by 6.4 steel shore posts spaced at 1.2 m on centre, bearing on timber mud sills, supporting an HSS 203 by 203 by 9.5 cross-member under the existing lintel; shoring engaged before masonry removal begins." Weak language: "temporary shoring as shown in the contractor's submission."
4. ASSESSMENT. The engineering opinion. What the engineer concludes about the adequacy of the proposed shoring against the load it has to carry, and under what conditions. This is the sentence the seal is attached to. Strong language: "Under the assumptions below and the loads in section 2, the proposed shoring is acceptable to carry the gravity load of the lintel and the tributary load on the wall above during removal of the masonry below." Weak language: "the shoring appears to be satisfactory."
5. LIMITATIONS. The outer boundary of the opinion. What the engineer did not review, what the engineer assumed, and under what conditions the opinion is no longer valid. This section is disproportionately important on a shoring letter and is treated in its own section below.
A letter missing any one of these sections has a structural gap. A letter in which one section is a single line has the same gap, less visibly.
The assumption and limitation bands that carry the most risk
Every sealed opinion letter ends with a limitations paragraph. On a shoring letter, four specific limitation bands show up often enough that their presence is diagnostic of the letter's defensibility.
The structure was built per the drawings. The engineer has reviewed the governing drawings but has not confirmed, and typically cannot confirm, that the element as built matches the element as drawn. Framing substitutions, deteriorated materials, and undocumented prior repairs are all possible, and all invalidate the opinion. The limitations paragraph names this assumption explicitly: "This opinion is based on the assumption that the existing structure was constructed in accordance with the drawings referenced above and that no modifications have been made since original construction that would affect the load path."
No post-construction modifications. Related, but specifically about the period after original construction. Previous tenant fitouts often add or remove elements that touch the load path of the element being shored. A floor slab that was cored for a service riser five years ago has a different capacity than the one on the drawings. The paragraph calls out the assumption that no such modifications have occurred, or lists those that have been accounted for.
Loads as represented. The letter's assessment is based on the loads identified in the documents reviewed and the loads the contractor has represented as applicable during the work. If the contractor stages materials on the shored assembly, if heavier equipment is brought in than was represented, if the sequence of work changes, the loads change. The limitations paragraph names this assumption so the letter is bounded to the condition the engineer reviewed.
Contractor's continuing obligation to monitor shoring during work. The engineer of record has reviewed a static arrangement against a static load. The contractor is responsible for monitoring the shoring throughout the work, for stopping work if deflection, tilt, or unexpected distress is observed, and for contacting the engineer if conditions change. The limitations paragraph makes this obligation explicit so the letter is not later read as the engineer's ongoing endorsement of conditions the engineer never re-inspected.
The four bands are the structural scope of the professional opinion. A limitations paragraph that carries all four with specific language bounds the engineer's liability to what the engineer actually reviewed. Generic language extends that liability to conditions the engineer never considered.
The defensibility traps
Shoring letters that fail under PEO complaint, dispute, or insurance review usually fail through one of a short list of recurring errors. Each trap is cheap to avoid and expensive to encounter.
Naming the element without naming the load. The letter describes the wall, the lintel, or the slab being supported without stating the load path and the value the shoring has to carry. The engineer knows; the letter does not say. In a dispute, the question becomes whether the engineer's judgment was informed by the right load, and the letter cannot answer.
Endorsing the contractor's methodology without describing it. The letter says "the contractor's proposed shoring is acceptable" and stops. A reviewer years later cannot reconstruct what was endorsed, and the contractor's submission may have been revised since issuance. The letter needed to reproduce, in its own words, the methodology it was accepting.
Missing limitations band. The letter names three of the four limitation bands and omits the fourth, typically "loads as represented" or "contractor's continuing obligation." The absence is rarely intentional. It happens when a letter is written from memory under time pressure and the firm does not have a checklist encoded in its template.
Naming an acceptance criterion without identifying the standard. "The proposed shoring is acceptable in accordance with good engineering practice" is not a citable basis. The letter has to identify the specific standard: OBC Part 4 for the demand on the permanent structure, the governing material standard (S16, A23.3, O86, S304) for capacity, the contract documents for any project-specific requirement. A bare appeal to engineering practice collapses under inspection.
Silent scope expansion. The letter reviews shoring for an interior partition, and the contractor also asks, verbally, about a ceiling joist two metres away that will need to be temporarily supported. The engineer says "that should be fine too" and the letter goes out without an explicit scope statement for the second element. In the file, the letter appears to cover both; in the engineer's memory, the second element was a verbal note. The gap between those two readings is where a dispute lives.
The regulatory and standards landscape
Shoring requirement letters sit under the same Ontario engineering framework as every other sealed document, with a handful of standards that touch the category more directly than others.
Ontario Building Code Part 4. Structural design provisions for the permanent structure. A shoring letter's assessment section usually references OBC Part 4 for the design loads on the element being protected, and the governing material standards referenced through Part 4 for capacity evaluation.
CSA S269 Formwork and falsework, with material standards for the shore members. S269 applies to temporary supports for concrete and other work. The shore members themselves are evaluated under whichever material standard governs: CSA S16 for steel shores (the HSS posts and cross-member in the strong-language example above), CSA A23.3 for concrete shoring, CSA O86 for timber. A shoring letter endorsing a full shoring design references whichever combination applies. The letter itself is not a design document under any of them.
PEO Regulation 941 section 53. The sealing obligation. A shoring requirement letter is an engineering document that contains the licensed professional's opinion. Section 53, as rewritten by O. Reg. 837/21 and in force since 2021, governs when the seal is required and the professional obligations it carries.
Ontario Regulation 213/91 on construction projects. The OHSA regulation governing construction sites in Ontario. Its provisions on supports, braces, and the removal of structural elements set the regulatory environment the contractor is operating under. A shoring requirement letter frequently intersects with those obligations even though the letter itself is not an OHSA submission. The letter's assumption about the contractor's continuing monitoring responsibility sits at the boundary between the engineer's professional obligation and the contractor's OHSA obligation.
Where this leaves the letter
A shoring requirement letter is a short document doing heavy structural work. Its five sections, four limitation bands, and named regulatory basis are cheap to include and expensive to omit. Firms that write shoring letters routinely usually encode the shape into their internal template, and younger engineers learn it by writing against that template. Firms that write them less often, or that have never codified the shape, produce shoring letters that vary in defensibility from engineer to engineer within the same practice.
A free audit tool for the category lives at /tools/letter-audit. Paste a draft shoring letter and get an independent read on scope clarity, named basis, assumption documentation, and limitations coverage. For firms interested in how Fermito drafts shoring requirement letters end-to-end from a PE's verbal brief, the demo is at /demo.
