A 5-bedroom contemporary detached on a former 1960s bungalow plot — ICF construction, triple-glazed aluminium throughout, ASHP, MVHR, and a SAP A98 energy rating against a pre-build target of A92.
A husband-and-wife client pair, both engineers, bought a tired 1960s three-bedroom bungalow on a quarter-acre plot in Alderley Edge with a single objective: knock it down and build the high-performance forever home they had been spec'ing on paper for the previous four years.
The brief landed with us at the same time as it did with two well-known regional developer-builders. Our pitch was different: we proposed building it the way they would specify it themselves — ICF wall system rather than block-and-render, MVHR designed in from sheet one rather than threaded through afterwards, and a single fixed-price contract that put the airtightness target on us, not on them.
We won the work on the strength of the M&E coordination plan and a willingness to underwrite the airtightness number. Eleven months later, the house tested at 0.9 air changes per hour at 50Pa — better than the 1.5 ach contracted target, and inside Passivhaus territory.
Both clients had degrees in engineering and had spent years researching low-energy construction. The brief was specific:
Total budget ceiling was £750,000 inclusive of VAT, demolition, fit-out and external works. The clients held an additional £25,000 contingency that we agreed would not be drawn against without written authorisation.
Five things made this build genuinely demanding rather than just expensive.
The 1960s bungalow contained AIB ceiling tiles in three rooms, Artex finishes, and cement-fibre soffits and bargeboards. All required licensed removal under HSE notification before any demolition could start. We engaged a licensed asbestos contractor for a 4-day removal phase before the demolition crew set foot on site.
ICF wall construction is straightforward in concept and unforgiving in execution. Block alignment, rebar placement, brace timing and concrete pour sequencing are all critical. We brought in a Cheshire-based ICF specialist crew who we had worked with on two previous projects and whose foreman attended every pour.
Mechanical ventilation has to be designed before walls go up, not after. Duct routes, terminal positions, attenuation pieces and the MVHR plant location were drafted into the architectural drawings before tender. Every plumbing, electrical and joinery trade was given the M&E drawings as their primary coordination reference.
Hitting a 1.5 ach@50Pa target on a brick-and-render house is hard. On an ICF build it should be easy — provided every penetration through the airtight layer is detailed and sealed. We ran a pre-test mid-build (week 28) at 1.8 ach, identified six problem penetrations, fixed them, and retested at 1.1 before plasterboard went up.
The plot sat at the end of a single-lane access road shared with three neighbouring properties. Concrete pump deliveries, ICF block lorries and the steel ridge crane each required pre-notified delivery slots, traffic marshals and direct neighbour liaison. Not a single complaint logged with planning during the entire build.
Eleven months meant building through one full Cheshire winter. ICF can be poured in cold weather with admixtures and thermal blankets, but the screed and plaster phases needed sequencing into milder months. The programme was built backwards from a target weathertight date in December.
High-performance new builds succeed or fail on coordination, not on materials. Our entire approach was built around that principle.
Design coordination before tender. Most contractors price a new build off architectural drawings and then negotiate the M&E. We insisted on a coordinated set of architectural, structural and M&E drawings before the contract sum was fixed. This cost both parties an additional six weeks at the start — and removed roughly forty potential mid-build variations from the schedule.
One contract, one team, one programme. Demolition, asbestos, groundworks, ICF, M&E, joinery, landscaping — all delivered under a single fixed-price agreement with one project manager and one weekly client meeting. No client coordination of separate trades. No gaps for risk to fall through.
Test airtightness twice, not once. A single airtightness test at completion is too late to fix anything. We commissioned a mid-build test at week 28, before the plasterboard layer concealed the airtight membrane and detail tape. Six problem penetrations identified and remediated. Final test result: 0.9 ach.
Commission, don't just install. The MVHR system was specified to be commissioned to balanced flow rates by the manufacturer's engineer, not signed off by our M&E sub-contractor. Same for the ASHP weather-compensation curve. Two extra commissioning visits, written reports issued to the clients, and the systems performed at design intent from day one.
Forty-five working weeks from asbestos survey to handover. Built backwards from a December weathertight target.
HSE-notified asbestos removal of AIB ceiling tiles, Artex and cement-fibre soffits. Existing services capped and isolated. Bungalow demolished and crushed on site for re-use as Type 1 sub-base. Plot surveyed and pegged out for new build.
Reduced level dig, drainage runs and stormwater attenuation crate installed, new electric and water services brought in. 300mm reinforced concrete raft slab poured with integral edge insulation. Building Control sign-off achieved on substructure.
Polystyrene ICF blocks dry-stacked to first floor, rebar tied off, concrete pumped into the formwork on a controlled fill cycle. First-floor pre-cast concrete plank deck installed. Second lift of ICF blocks to eaves level, second concrete pour. Roof structure ready to be set out.
Engineered timber roof structure with steel ridge over the principal living space. Warm-roof insulation build-up, EPDM weatherproof membrane, standing-seam zinc cladding to flat sections, slate to pitched. Triple-glazed aluminium openings craned in and installed. Weathertight on day 132 — six days inside the December target.
MVHR ducting installed first, before plumbing or electrical, with all routes following pre-tendered drawings. ASHP external unit positioned and commissioned for cold-weather operation. Wet underfloor heating loops installed and pressure-tested. Cat-6 data, smart lighting bus and AV cabling all run during first fix.
Internal airtight layer detailed, taped and inspected. Mid-build pressurisation test performed at week 28: 1.8 ach against a target of 1.5. Six problem penetrations identified and remediated. Retest at week 30: 1.1 ach. Plasterboard installed across all internal partitions and ceilings.
Skim plaster to all walls and ceilings. 75mm liquid screed poured over UFH loops, allowed to cure for 28 days. Second fix electrical and plumbing through dried-out fabric. Bespoke kitchen, sanitaryware, internal joinery installed.
Internal decoration to all rooms. MVHR commissioned to balanced flow rates by manufacturer's engineer. ASHP weather-compensation curve set and tested across two cold-weather days. Smart-home bus configured and walk-throughs delivered to clients.
Rear garden landscaped: poured-concrete patio with integrated lighting, retaining walls, planting and lawn. Final airtightness test logged at 0.9 ach. SAP final assessment returned A98. Building Control completion certificate issued. Keys handed over with a 56-page operations and maintenance manual.
A high-performance specification with the supporting numbers.
300mm reinforced concrete raft slab with 200mm Kingspan K103 perimeter edge insulation and integral cold-bridge break detail.
Nudura 300mm ICF system: 70mm EPS / 150mm reinforced concrete core / 70mm EPS. Wall U-value 0.15 W/m²K. Thermal mass benefit retained on internal face.
Warm-roof construction: 200mm PIR insulation, EPDM weatherproof membrane, standing-seam zinc cladding to flat sections, natural slate to pitched. Roof U-value 0.11 W/m²K.
Schueco AWS 75 aluminium triple-glazed throughout, anthracite grey RAL 7016, whole-window U-value 0.8 W/m²K. 6.2m sliding door to principal living space.
Mitsubishi Ecodan 14kW air source heat pump, weather-compensated, feeding wet UFH throughout ground floor and first floor. 300L unvented hot water cylinder.
Zehnder ComfoAir Q450 MVHR with 92% heat recovery efficiency, balanced supply and extract, manufacturer-commissioned with written flow report.
8.4 kWp roof-integrated solar PV array with 10kWh battery storage. EV charging point pre-installed at outbuilding. Estimated annual generation 7,200 kWh.
Loxone Tree-based smart-home system: lighting, heating zones, MVHR boost, blinds, security and AV all integrated on a single bus with mobile and wall-panel control.
A 312m² contemporary detached home with a measured airtightness of 0.9 ach@50Pa, a SAP A98 rating, and predicted annual heating-and-hot-water running costs of approximately £640. The clients have moved in, completed a winter, and reported actual energy bills 8% below the SAP-modelled prediction.
Forty-five working weeks against a contracted forty-five. Fixed price held. Contingency untouched. The build is now used by the ICF block supplier as one of three reference projects for prospective clients in the region.
We're both engineers and we read the contract twice before signing it. The thing that won us over wasn't the price — the others were within five percent. It was that Building Group were the only firm willing to put the airtightness number on themselves and to test it twice. The mid-build pressurisation test on week 28 found six issues we would never have known about until completion. That single decision is why the house performs the way it does.
If you're planning a new build — ICF, timber frame, masonry — we'll come out for a free site visit, talk through your performance targets and put a fixed-price contract on the table. No surprises, no escalation, contractor-warranted airtightness.
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