Self-builders who bring in their solar designer or installer late, at RIBA Stage 4 or later, often pay more, fit a smaller array than the roof could carry and get a less integrated finish. The right time to involve them is RIBA Stage 2.
RIBA Stage 2: concept design
At concept design, the solar designer gives the architect initial sizing, an indicative kWp range and guidance on roof form, and flags the trade-offs: a simple south-facing roof can carry a larger array than a complex, broken-up one.
RIBA Stage 3: spatial coordination
Array layout, structural loadings, inverter location and cable routes are agreed, and the roof layout drawing is incorporated by the architect. Preliminary SAP modelling begins.
RIBA Stage 4: technical design
The specification goes into the tender pack: panel make and model, inverter, in-roof mounting, monitoring, MCS certification and warranty terms. The SAP design-stage calculation is finalised for the building control submission.
RIBA Stage 5: manufacturing and construction
The in-roof mounting goes in before tiling or slating, with the installer coordinating with the main contractor and roofer. Panels and inverter follow, then commissioning, the MCS certificate, the EPC and handover at completion.
After completion (RIBA Stage 7)
Keep the installer’s workmanship warranty (check whether it is insurance-backed), the panel and inverter manufacturers’ warranties and the monitoring login together, and know who to contact if something goes wrong.