Why GBIS, and what it covered
The Great British Insulation Scheme was designed exactly for households like the Harts: owner-occupiers on a moderate income in a lower-banded property with untreated insulation gaps. Cavity wall insulation is funded in full under GBIS. Room-in-roof is partially funded — the scheme pays a fixed contribution toward it and the homeowner tops up the balance.
EDF Energy was the obligated supplier on the Harts' application. We filed the eligibility paperwork at survey stage and had scheme approval back in 8 working days.
What we installed
Blown-bead EPS cavity wall insulation across the full perimeter — one day, no disruption inside the house. Room-in-roof insulation in the two dormer bedrooms: PIR insulation fitted between the rafters, with a continuous over-rafter layer to break the thermal bridging at the rafter line, dressed and finished to the existing plasterboard.
The Harts' contribution was £420, covering the top-up on the room-in-roof element. The cavity work was £0 to them. Everything was invoiced as a single line and the GBIS portion was drawn directly from EDF.
What we ruled out
A heat pump came up. The homeowner had a working A-rated combi installed in 2023 and a tight household budget. We told them straight: replacing a working three-year-old combi with a £12k+ heat pump install would never pay back inside their planning window.
The cavity and room-in-roof insulation did the heat-loss reduction. Heat pump conversation parked until the boiler reaches end-of-life.
The outcome
Post-install EPC re-rate confirmed D 62 → C 74. Metered gas use dropped from 14,500 kWh to 10,100 kWh across the first months of post-install bills, projected to £370/year saved at current rates.
The real change is behavioural: the family are using the upstairs bedrooms again. Evening bedtime routines are back upstairs instead of camping in the living room, and the kids' rooms stay usable even on sub-zero nights.
“The upstairs bedrooms used to be a no-go zone in winter — we'd all pile downstairs. Four months on and the kids are actually using their rooms in the evenings. Best £420 we've ever spent.”