What Is Included in a Desktop Structural Report: The Engineer's Contents List

A desktop structural report for commercial solar PV is the document that allows a structural engineer to confirm a roof's structural adequacy without visiting the site, using existing drawings, specifications, and the proposed array design to conduct a full loading assessment from desk. Understanding what a competent desktop report contains helps clients brief structural engineers accurately, evaluate report quality, and use the output effectively for MCS certification, lender due diligence, and insurance purposes.

This article explains the five core sections of a desktop structural report, what each section should contain, and the common deficiencies that cause reports to be rejected by certification bodies or lenders.

Why Desktop Reports Are the Standard Starting Point

For commercial solar on buildings with existing structural drawings, a desktop report is the most efficient way to obtain structural sign-off. It avoids the cost and programme implications of a site survey (typically 2-4 times the cost and 5-10 times the lead time), and in many cases provides a conclusion that is just as robust as a site-based assessment.

The desktop report approach is appropriate where:

• Complete structural drawings are available: general arrangement, sections, and structural schedules
• The as-built structure is consistent with the drawings (no undocumented modifications)
• The structural form is standard, portal frame, concrete frame, or masonry, using recognised section types
• The proposed array layout is finalised and consistent with the drawings (e.g., panel positions do not fall on structural elements that can't be identified from drawings)

Where any of these conditions is not met, a site survey is required to supplement or replace the desktop assessment. The structural engineer makes this determination at instruction, not at report production, if the drawing pack is incomplete, the engineer should flag this before starting work rather than producing a report with caveats that it cannot be relied upon.

Section 1: Project Description and Scope

The opening section of a desktop structural report establishes the scope of the assessment: what is being assessed, against what standard, and for what purpose. A robust project description section includes:

Property identification: Full address, building description, and reference to the structural drawings reviewed. The drawings should be identified by drawing number, title, and revision, not by generic description. "Portal frame GA drawings" is insufficient; "Drawing ref. 1234-SA-001 Rev B, Structural General Arrangement, dated 15 March 2022" provides a traceable reference.

Purpose of the assessment: Whether the report is for MCS Section 5.9 compliance, lender due diligence, planning application, or another purpose. Different purposes may require different levels of detail or different sign-off formats.

Standards applied: The Eurocodes and National Annexes used in the assessment: BS EN 1990, BS EN 1991-1-1, BS EN 1991-1-3, BS EN 1991-1-4, and the relevant material standard (BS EN 1993-1-1 for hot-rolled steel, BS EN 1993-1-3 for cold-formed steel, BS EN 1995-1-1 for timber).

Limitations and assumptions: Any assumptions made in the absence of specific data, for example, assumed material grade if the drawings do not specify it, or assumed connection capacity if connection details are not shown. Limitations must be stated explicitly so the reader understands where additional investigation might be required.

Section 2: Building Description and Structural Form

A competent desktop report demonstrates that the structural engineer understands the building, not just the numbers. The building description section covers:

Construction type and age: Portal frame, concrete frame, masonry, or mixed. Approximate construction date (relevant to understanding likely material grades and construction quality).

Roof structure: Primary frame members (section type and designation), secondary members (purlin type, spacing, and span), roof deck (profiled metal, timber boarding, or concrete), and roof covering (cladding type, insulation, membrane).

Existing roof loads: Confirmed from drawings or specification: cladding self-weight, insulation, any services or plant. This is the baseline load against which the incremental solar array load is checked.

Critical structural elements identified: Which element in the structural hierarchy is likely to govern the assessment, typically the purlins in a portal frame building. Identifying the critical element before the calculation demonstrates engineering judgment, not just calculation execution.

Section 3: Proposed Solar Array Description

The solar array description links the structural assessment to the specific installation being assessed. A desktop report that doesn't adequately describe the proposed installation cannot be relied upon as MCS sign-off, the MCS certification body needs to confirm the report covers the installed system.

The array description must include:

• Panel specification: Manufacturer, model, dimensions, and weight per panel
• Array layout: Reference to the array layout drawing, panel count, row spacing, and tilt angle
• Mounting system: System type (seam clamp, through-fix to purlin, ballasted), manufacturer where applicable, and fixing pattern
• Total array dead load: Calculated distributed load in kN/m², panels plus mounting system plus any ballast

Section 4: Loading Calculations

The loading calculations are the technical core of the desktop report. A report without explicit load calculations, one that states only "the roof is adequate" without showing the work, does not meet the technical standard expected of a Eurocode-based structural assessment and will not be accepted by lenders or professional certification bodies.

The loading section must cover:

Dead load: Existing dead load on the roof structure (cladding, insulation, services) plus the proposed array dead load. Expressed per unit area (kN/m²) and as a total load on the critical structural element.

Wind load: Full wind speed calculation to BS EN 1991-1-4 NA, showing: basic wind speed (from wind speed map, interpolated for site location), terrain category, building height, and peak velocity pressure. Followed by pressure coefficient application for each roof zone (internal H, edge G, corner F for flat roofs; zones by pitch and wind direction for duopitch roofs). Design uplift pressure in kN/m² for each zone, clearly labelled.

Snow load: Characteristic ground snow load from the UK NA map, shape coefficient applied, design snow load in kN/m².

Load combinations: Application of BS EN 1990 partial factors and combination rules to produce design loads for the governing combinations, typically wind-dominant uplift and dead-plus-snow downward loading.

Structural element checks: Using the design loads from the combination calculations, section capacity checks for the governing structural elements. For cold-formed purlins, this means moment capacity check to BS EN 1993-1-3. For fixing adequacy, design force per fixing location versus fixing resistance from manufacturer data or pull-out test results.

The calculations must show clearly that the design load is less than the capacity with an appropriate factor of safety. A calculation that simply states "capacity: 8.2 kNm; design moment: 7.9 kNm; utilisation ratio: 0.96" is appropriately detailed. A calculation that states "the purlins are adequate" without numerical demonstration is not.

Section 5: Conclusions and Sign-Off Statement

The conclusions section translates the technical calculations into a clear statement of structural adequacy, the statement that MCS certification bodies, lenders, and insurers will rely on. A robust conclusions section contains:

Structural adequacy statement: An explicit statement that the existing roof structure is adequate to carry the proposed solar array as described in Section 3, without structural modification. Or, if modification is required, a clear description of what modification is necessary.

Conditions on the clearance: Any conditions attached to the structural clearance, for example, fixing positions must follow the pattern shown on drawing ref. X; corner zone ballast must use the increased weight specified in the calculation; installation must be completed within a specified timeframe if the assessment was conducted on a building known to have a structural issue under monitoring.

Engineer details: The report must be signed by a named structural engineer with their professional body membership number. The signing engineer's name and qualifications must be verifiable through their professional institution's online register. Unsigned reports, or reports signed by a generic company signature rather than a named engineer, do not satisfy MCS requirements.

Validity statement: Confirmation that the report is valid for the array as described, and that any material change to the array specification, layout, or mounting system will require the report to be reviewed and, if necessary, updated.

Common Desktop Report Deficiencies

Desktop Reports for Lender Due Diligence

Lenders commissioning due diligence on financed commercial solar assets typically require a higher standard of desktop report than the MCS minimum. Lender Technical Advisers (LTAs) will review the report and may request:

• The full calculation pack (not just the report, the underlying calculation sheets as an appendix)
• Professional indemnity confirmation letter from the engineer's insurer, specifying coverage amount
• A firm-level sign-off, the report signed on the structural engineering firm's letterhead, with the firm's PI rather than the individual engineer's PI only
• An independent check, a second structural engineer reviewing the calculations for errors

For projects where lender due diligence is anticipated at financing or refinancing, commissioning the structural report to lender-standard from the outset avoids the need to produce a supplementary document later. The incremental cost of including the calculation pack and arranging PI confirmation at initial instruction is small; the cost of renegotiating a structural appointment to add these elements post-instruction is higher.

Retaining and Managing Desktop Reports

A desktop structural report is a long-lived document that will be referenced throughout the asset's life: at MCS certification, at insurance renewal, at refinancing, at asset sale, and potentially in the event of a structural incident. It should be stored in the project file in a durable, retrievable format, not just in an email thread that will eventually be deleted.

The project file should include: the signed report (PDF), the drawing set reviewed (PDF or DWG), the array layout drawing that the report was prepared against, and the engineer's PI confirmation. Where the structural engineer produced a calculation pack in addition to the report, the calculation pack should also be retained.

At asset sale or lease assignment, the structural report is part of the technical due diligence package. An asset manager who cannot produce the structural report for a solar installation on their building will face questions from the buyer's technical advisers that delay completion and may reduce the perceived value of the asset.

Supplementary Deliverables: Wind Zone Plans and Fixing Schedules

A complete desktop structural report for commercial solar PV may include supplementary deliverables beyond the main clearance document. These supplementary outputs address specific technical questions that the clearance verdict alone does not resolve, most importantly, how the wind uplift load varies across the roof and what fixing specification applies to each zone.

A wind zone plan is a scaled roof plan annotated with the wind load zones defined by BS EN 1991-1-4. For rectangular flat or pitched roofs, the zone geometry follows the standard code classification: Zone A (corner zones, highest pressure coefficients), Zone B (edge zones), and Zone C (central field zones, lowest pressure coefficients). The plan annotates these zones against the actual roof dimensions of the assessed building and states the net design wind uplift force per unit area for each zone, from which the racking installer can determine the required fixing capacity per attachment point in each zone. This plan removes the need for the installer to interpret the wind load clauses of the structural report and directly tells them what fixing centre or capacity is required at any location on the roof.

A fixing schedule takes the wind zone analysis one step further, specifying the recommended fixing type, minimum centre-to-centre spacing, and minimum edge distances for each zone on the roof, based on the design uplift forces and the pull-out capacity of the proposed fixing in the identified roof substrate. A fixing schedule is the most directly actionable structural deliverable for the installation team: it is used as the installation instruction document for fixing placement rather than requiring the installer to translate from wind load analysis to fixing specification independently.

Not all structural reports include these supplementary deliverables as standard. Where the clearance is unconditional and the wind loads are not exceptionally high, the main report conclusions may be sufficient for the installer to proceed using the racking manufacturer’s standard fixing specification. Where conditions are stated, or where wind loads are elevated due to site exposure or building height, supplementary deliverables provide the additional detail needed to implement the conditions correctly.

Report Versioning and Amendment: Managing Design Changes

Commercial solar projects frequently undergo design changes between the initial structural assessment and the final installation. Panel substitutions, racking system changes, array layout revisions, and inverter relocation all have potential structural implications, and the structural report must reflect the installation that was actually built, not the design that was originally assessed. Understanding how report versioning and amendment processes work prevents compliance gaps between the assessed design and the as-installed installation.

Minor design changes, a panel substitution that reduces the dead load, a racking system change that is within the same weight class as the originally assessed system, typically require only a confirmation note from the structural engineer rather than a full report revision. The confirmation note states that the revised specification has been reviewed and is within the parameters of the original clearance assessment. This note is appended to the original report in the project file and referenced in the MCS documentation.

Material design changes, a panel substitution that increases the dead load beyond the stated limit in the original report, an array layout extension into a new roof zone not covered by the original assessment, or a racking system change that involves fundamentally different attachment or loading characteristics, require a formal report revision or supplementary assessment. The revised report supersedes the original for the elements affected by the design change, and the project file should retain both versions with clear identification of which is current.

Managing design changes against the structural clearance is the project manager’s responsibility. A simple change control protocol, documenting each design change, forwarding it to the structural engineer for confirmation whether the change is within the existing clearance parameters, and filing the confirmation in the project record, prevents the situation where a completed installation diverges from the assessed design without the structural engineer’s knowledge or confirmation.

WHERE SOLAR SURVEYS ADDS VALUE