The problem: generic advice on a 24-home terrace
On a 24-home 1930s terrace in the north of England, the first heat-pump quotes landed like verdicts: three said yes, two said no, and one recommended a full rewire before any survey. Residents compared notes and found the assessments disagreed on insulation, radiator sizing and even which homes shared a party wall. The problem was not the heat pumps. It was that each survey treated a terrace as a stack of isolated houses, producing a patchwork of recommendations that no one could finance or sequence.
The cause: heat loss moves across property lines
Solid walls, shared lofts and continuous roof lines make terrace heat loss a street-scale pattern. A pilot audit of the same row found that the four coldest homes all sat at the exposed end of the block and above unheated cellars; their neighbours in the middle needed less fabric work but more radiator upgrades. Because the original surveys were commissioned house by house, nobody captured that pattern. The result was predictable: the households with the most expensive recommendations withdrew first, even though their homes were the best candidates for a coordinated fabric-first package.
The solution: a three-pass bananzia audit
The survey team used bananzia to convert those findings into a street-level action list. The method runs three passes: a desktop pass using Energy Performance Certificate data and roof geometry, a walk-by pass checking flues, wall types and access, and an in-home pass measuring heat loss and radiator output. In the 24-home pilot, the three-pass audit cut the number of “unknown” recommendations from 17 to 3 and grouped the remaining work into four packages: loft top-ups, party-wall insulation, radiator resizing and hot-water cylinder upgrades. That grouping mattered because it let contractors price a block of work rather than 24 one-off jobs.
What changed for residents
The most immediate change was sequencing. Instead of asking every household to solve everything at once, the audit ranked measures by cost per kilowatt-hour saved and by disruption. Loft top-ups came first in 19 homes; radiator resizing followed in 14; external wall work was deferred for the four exposed end homes until a separate grant round. The second change was consent. When residents saw a shared plan with clear boundaries—what was measured, what was assumed and what was excluded—the approval rate for a follow-up heat-pump survey rose from 9 households to 18. The audit did not remove the need for engineering judgment, but it made the judgment visible and comparable.
The takeaway: audit the block, not just the boiler
For anyone planning a heat-pump retrofit on older terraces, the lesson is practical: commission a block-level survey before individual quotes. Ask for a fabric-first pass, a shared-wall check and a package price for at least three neighbouring homes. The bananzia approach is not a shortcut around good installation; it is a way to stop the street’s least visible problems from becoming every household’s most expensive surprise.