About retrofitcost.co.uk
About retrofitcost.co.uk: a surveyor's working file on UK house retrofit cost, written by Oliver Wakefield-Smith, Founder of Digital Signet.
What this file is
retrofitcost.co.uk is a working file. It treats the reader as a literate adult deciding whether to commit fifty thousand pounds of late-career capital. It is not a marketing brochure. It is not affiliated with any installer, scheme or coordinator. It carries no affiliate links to vendor sites; the only links into vendor pages are publisher anchors used as citations.
What it is not
It is not a Retrofit Assessor and it is not a Retrofit Coordinator. The figures here frame the conversation before those fees are spent; they do not replace them. Any project that pulls on ECO4, GBIS or the Warm Homes Plan must engage a real PAS 2035 Coordinator.
How figures are verified and refreshed
Every numeric claim resolves to a primary source on the sources manifest. The Ofgem cap for 1 October to 31 December 2026 (gas 7.97p, electricity 26.32p, gas standing 29.68p, electricity standing 54.83p) is applied site-wide and is refreshed on Ofgem's quarterly cycle, which means the next scheduled review is 25 November 2026, when the January rates are announced.
Two model inputs are not published figures and are labelled as such wherever they appear. The heat pump SPF of 2.78 is the median delivered performance across 428 monitored installations in the Electrification of Heat Demonstration Project, which is a measurement, not a design target, and the calculator lets you change it. The boiler seasonal efficiency of 85% is an assumption: that trial did not monitor boiler efficiency, so the honest band is the 76% to 92% its own hybrid-system matrix spans, and 85% is this file's mid-band pick. Both sit in the calculator as inputs you can overwrite, because a number you cannot interrogate is not a number you should trust.
Author
Oliver Wakefield-Smith, Founder, Digital Signet. Corrections to oliver at digitalsignet dot com.