Why this property
Conservation Area status meant external wall insulation was a non-starter on the front elevation — the Victorian brickwork and original detailing had to be preserved visually. Internal wall insulation (IWI) was the only viable solid-wall option, applied to the front living room and the master bedroom directly above it. The rear extension was a later 1970s build with a cavity, treated as a separate scope.
The loft conversion had 75mm of available rafter depth. PIR at the U-value the building inspector required would have needed 110mm. Mineral wool would have needed 270mm. Multifoil was the only product that fit while still hitting the 0.18 W/m²K target.
What we installed
IWI: 60mm phenolic-backed plasterboard with an integrated VCL, fitted to the rear of front living room and bedroom — total area 38 m². Window reveals lined to break the thermal bridge. Existing electrical sockets and radiator pipework all relocated to the new face. Three days from start to skim.
Multifoil: Actis Hybris HCONTROL between rafters with a 25mm batten cavity outboard and a 25mm batten cavity inboard, finished with 12.5mm plasterboard. All overlaps taped to BBA spec. The room-in-roof finished surface dropped 97mm from the original ceiling line — barely noticeable on a 2.4m head height.
Cavity wall (rear extension): blown EPS bead, single day, no internal disruption.
The outcome
Post-install EPC came back at C 71 — a two-band uplift from the starting E 49. ECO4 covered the IWI and cavity work in full; the multifoil came in under ECO4 LA Flex Route 2 (one of the children has asthma, qualifying as cold-vulnerability). Total customer contribution: £0.
The loft conversion is now usable year-round. The IWI on the front rooms eliminated the cold-spot patches that used to drive the heating system into constant cycling. Modelled annual saving: £1,120/year, which the first three months of bills are tracking close to.
“We assumed the loft conversion was a write-off in winter. The multifoil install took two days and now my office up there stays warm down to single digits outside. The IWI on the front rooms made the whole house feel different — calmer, quieter.”