Guide
Commercial solar engineering screening flags
Most commercial solar projects fail late because nobody screened the engineering and regulatory risks early. Stage1Energy flags four categories in every feasibility report - wind, structure, DNO, and planning - with a clear next step for each.
Why engineering flags matter at feasibility stage
Commercial rooftop solar projects often look viable on headline yield and payback - until a structural engineer, DNO, or planning officer raises an issue that changes the economics or timeline. Screening those risks at feasibility stage, before you commission surveys and design, saves money and gives boards an honest picture.
Stage1Energy does not certify structures or submit grid applications. The report flags where professional verification is likely needed and names the next step. That is feasibility, not design - but it prevents surprises.
Flag 1 - Wind loading
Uplift screening flags this roof for early structural input. Roofs in this band commonly need ballast or fixing changes that move capex - get the mounting supplier’s calculation before you budget.
If uplift exceeds typical ballast capacity or the roof covering cannot accept penetrations, the flag names structural follow-up. Deep dive: wind loading on commercial roofs.
Flag 2 - Structural capacity
Indicative dead-load intensity for feasibility triage. Excludes roof structure self-weight, wind, snow and existing roof capacity. Confirmation by a structural engineer is required before design.
When the screening ratio is marginal, the report recommends formal structural assessment before procurement. Read: structural screening for commercial roof solar and feasibility vs structural survey.
Flag 3 - DNO and grid connection
Preliminary G98/G99 route by installed capacity. Phase, export limiting and fuse rating are not assessed - confirm with the DNO.
The feasibility report identifies the likely G98/G99 route based on proposed system size and flags when export capacity or queue risk could affect project economics. Guide: G98 vs G99 explained and DNO applications for commercial solar.
Flag 4 - Planning and permitted development
Many UK commercial rooftop installations may fall under permitted development rights (TCP(GPDO) 2015 Class A/J), but exceptions apply - conservation areas, listed buildings, Article 4 directions, and height limits can require full planning permission. Screening is indicative; verify with the local planning authority.
The report runs a permitted development screening check and states the likely planning route. If full planning is probable, the flag notes timeline and cost implications. Read: permitted development for commercial solar.
How flags appear in the report
Each flag is stated plainly in the engineering section of the 29-page report - not buried in small print. A flagged item includes what was checked, what assumption was used, and what professional verification is recommended next.
See real examples in the example report (engineering flags section) and the full engineering flags guide. Our approach: methodology page.
Questions
FAQ
Are engineering flags in a feasibility study legally binding?
No. They are screening outputs based on desk-based data and published methods. Structural, wind, grid, and planning conclusions require verification by appropriately qualified professionals before construction.
Can a feasibility study clear all four flags?
Yes, when desk-based screening finds no obvious issues. Many commercial roofs pass all four at feasibility stage. Others flag one or more areas for follow-up - that is the point of screening early.
Do I still need a structural engineer if the flag is clear?
Many funders and landlords require formal structural sign-off regardless of screening outcome. The feasibility flag tells you whether that appointment is likely to be routine or may surface material issues.