Structural failure is the nightmare scenario commercial solar programmes rarely discuss in board papers — until a survey reveals the portal frame cannot support ballast loading or the deck needs strengthening. Feasibility exists partly to catch those cases early, at screening cost, before you appoint structural engineers on roofs that fail economically once strengthening is priced.
Understanding the difference between feasibility structural flags and a formal structural survey keeps spend in the right order and expectations honest.
What feasibility contributes on structure
Commercial solar feasibility includes structural screening, not structural certification.
At this stage the assessor reviews available information — building age, construction type visible from imagery or records, roof pitch, parapet height, known plant loads, and typical mounting approaches for that building class. The output is a flag: likely straightforward, needs confirmation, or potential showstopper.
Examples of screening language:
- “Steel portal frame warehouse — ballast mounting likely feasible subject to engineer confirmation.”
- “Unknown deck capacity on 1980s built-up roof — structural survey required before layout finalisation.”
- “Heavy plant at roof level — verify spare capacity before adding PV load.”
Stage1Energy dossiers treat these as flags requiring verification by appropriately qualified professionals — consistent with our disclaimer and methodology.
For where structural notes sit in the wider report, see what is in a solar feasibility report.
What a structural survey delivers
A structural survey (or structural calculation pack) is prepared by a qualified structural engineer for a defined mounting system and layout.
Deliverables typically include:
- Review of as-built or inferred structure
- Assessment of dead, live, snow, and wind loads including PV arrays
- Ballast weights or penetration details
- Identification of strengthening works if required
- Professional sign-off for insurer, landlord, and building control as needed
This work is site-specific and often requires site attendance, core samples, or review of original drawings. Liability rests with the engineer.
Cost reflects that depth: commonly £2,000–£5,000 on commercial rooftops, more if strengthening design is needed.
Why feasibility must come first
Ordering structural surveys before testing business case and coarse structural plausibility wastes money at scale.
If feasibility says payback is eight years on a marginal load profile, a £4,000 survey is hard to justify. If feasibility flags a likely deck overload, you may decline the site without survey. If feasibility is positive with “confirm structure,” survey spend is authorised with purpose.
That sequencing supports when to order a solar feasibility study and solar investment board papers: boards approve survey budget after feasibility, not in parallel with guessing.
Stage1Energy’s site assessment is designed to run before specialist survey spend — see solar feasibility study cost in the UK.
Wind loading sits between both stages
Wind uplift and ballast requirements bridge feasibility screening and structural sign-off. Feasibility may note exposed elevation, valley location, or high parapets as wind risks. Detailed wind load assessment feeds the structural calculation.
Some projects need specialist wind tunnel or CFD work — rare on typical warehouses but relevant on tall city buildings. Feasibility should flag unusual exposure even when full analysis waits for later.
Roof condition is related but separate
Membrane age, ponding, asbestos deck suspicion, or failed fixings are roof condition issues, often surveyed by roofing specialists rather than structural engineers alone.
Feasibility may flag “roof refurbishment recommended before PV” from imagery and age. A roof condition survey confirms watertightness and warranty compatibility with penetrations.
Do not install on a failing deck because structure alone passed — both tracks matter.
Comparison table
A structural survey costs £2,000–£5,000 whether the roof works or not. Screening first means that spend only lands where it can pay back.
| Aspect | Feasibility structural screen | Structural survey |
|---|---|---|
| Author | Feasibility analyst | Chartered structural engineer |
| Site visit | Usually remote | Usually required |
| Output | Risk flag and recommendation | Calculations and sign-off |
| Liability | Screening only | Professional duty |
| Typical timing | Before business case approval | After positive feasibility |
| Typical cost | Feasibility stage (see pricing) | £2,000–£5,000+ typical |
Interaction with design
Detailed design cannot finalise mounting until structural survey returns. Installers who promise fixed layouts before survey are assuming risk you may not want to carry.
Feasibility layouts should be flexible enough to shrink if structure or wind requires lighter arrays.
Portfolio considerations
On portfolios of similar warehouses, one structural survey on a representative building sometimes informs others — but only where construction is genuinely identical and a competent engineer agrees. Feasibility screening still runs per site because plant, age, and modifications differ.
Portfolio solar feasibility screening ranks which sites merit survey spend in year one.
Using Stage1Energy output
Positive feasibility with structural conditions means: brief your structural engineer with the dossier layout, mounting preference, and flags. Attach the feasibility PDF to survey instructions so the engineer knows the capacity range under discussion.
If feasibility is negative on structural grounds — e.g. clearly insufficient deck for economic array size — do not commission survey unless building works will change capacity.
Start with free screening on uncertain sites, then full commercial solar feasibility before survey quotes. Review structural sections in our example report for the level of detail feasibility provides — and what it deliberately does not.
Feasibility asks “should we pay for a structural engineer?” The survey answers “what must they design?”
Insurer and landlord requirements
Many commercial leases and insurance policies require professional sign-off for roof loading changes, even when feasibility screening looks benign. Feasibility should note when landlord consent or insurer notification is likely — separate from the structural calculation itself but often on the critical path.
Factor survey lead times into programme planning. Busy structural engineers on commercial roof work may need several weeks to attend site and issue calculations. A positive feasibility verdict is the trigger to book that diary slot, not the installer’s first available crane date.