Victorian terrace + KNX smart home + circadian lighting, Balham SW12

Brief

1898 Victorian mid-terrace SW12 Balham — 165m² over two storeys + loft, 220m² plot, sash + 1970s uPVC mix, original cornices + ceiling roses surviving in reception + master bedroom, original pitch-pine floorboards under 1990s carpet, rear yard 80m². Owners (tech founder + GP + 2 children) brief: premium whole-house renovation with KNX smart home + John Cullen circadian lighting scheme + ASHP retrofit + side-return + loft conversion + heritage sash restoration. KNX bus wiring throughout for lighting + heating + blinds + audio + security. Circadian lighting in master bedroom + study + kitchen-living open-plan. Side-return + L-shape dormer + master suite reconfigure. Budget £425,000 (£2,575/m²). Wandsworth permitted development for side-return (no CA); pre-application for loft + bus wiring strategy.

Challenge

Six layered constraints. (1) KNX whole-house bus + circadian scheme at first-fix — KNX cable + tunable white wiring + DALI driver locations + DALI Group addressing planned at RIBA Stage 3 (chase + cable routes locked before plastering); single-vendor KNX integrator (Sound Servic) coordinating with lighting designer (John Cullen Lighting, mid-tier studio) + Builderr first-fix electrician — 3-party design coordination critical to avoid retrofit. (2) Heritage retention — 96m of original cornice across 4 rooms + 6 ceiling roses + pitch-pine floors + 7 of 14 original sashes survived; restoration tight tolerance not to disturb during MVHR + KNX bus routing. (3) ASHP retrofit + 18-radiator replacement — Vaillant aroTHERM Plus 8kW with 250L cylinder, all radiators replaced with oversized Bisque Classic 3-Column matt black (45°C flow design); BUS grant £7,500. (4) Side return + L-shape dormer = 38m² net new floor area; rear extension over Thames Water sewer = build-over agreement (£2,800). (5) MVHR design — Vent-Axia Sentinel Kinetic FH 250 in loft plant — 11 supply + 8 extract; semi-rigid 90mm duct routing through dropped ceilings + floor voids (preserving cornices). (6) Family in occupation 16 of 24 weeks — phased so wet-trade-heavy weeks 1–8 family vacated to in-laws; second-fix weeks 9–24 family back with rotating room access.

Solution

Pre-design 16 weeks. Architect (Architype Ltd) RIBA Stage 4 with KNX integrator + lighting designer + MVHR designer + structural engineer — 4-discipline weekly coordination. KNX design: 76 KNX devices specified (lighting + blinds + heating + security + audio); DALI bus topology (4 DALI groups — Living/Dining, Master, Children, Service); ABB Free@home KNX integration. Lighting scheme: 142 tunable-white LED downlights (Collingwood Halers H2 Lite Pro 1800–2700K dim-to-warm) + 28 standard LED downlights + 14 pendants (Tom Dixon Beat clusters, Lee Broom Crescent) + 38m LED cove strip tunable-white + 8 wall sconces (Original BTC). Circadian curve programmed: 1800K dawn → 2700K morning task → 3500K noon focus → 2700K evening → 1800K wind-down → 1500K night safety wayfinding. Build 24 weeks. Weeks 1–4 strip-out + first-fix prep (family vacated week 1). All non-heritage finishes removed — 1990s kitchen, 1970s uPVC windows (3 remaining), 1990s carpet over pitch-pine boards lifted carefully. Original pitch-pine boards numbered + lifted for re-laying. Heritage cornices + ceiling roses + dado/picture rails protected with PE film + plywood enclosure (zero damage tolerance). Weeks 5–8 structural (side return foundation + dwarf wall + steel beam over rear opening 5m clear span; loft conversion structural — L-shape dormer + party-wall hip-to-gable; Thames Water build-over agreement secured). Weeks 9–12 first-fix services. KNX bus cable (green Helu KNX) pulled from CU to every smart-switch position + every DALI driver point + every blind motor; standard 1.5mm² T+E for power circuits. 18-way RCBO Hager Design 30 CU + ABB KNX gateway + 4× DALI broadcast controllers in plant cupboard. MVHR first-fix Sentinel Kinetic FH 250 in loft plant zone + radial 90mm semi-rigid duct routes — all routed through dropped hallway/en-suite ceilings + floor voids (cornices entirely preserved). ASHP first-fix — Vaillant aroTHERM Plus 8kW external rear yard + 250L pre-plumbed cylinder loft. Weeks 13–18 second-fix + heritage restoration. Sash window restoration — 7 originals restored in situ by Ventrolla (re-corded, parting beads, slim 8mm DG conversion preserving original glass £1,400/window × 7 = £9,800); 4 replacements Mumford & Wood Conservation Range slim DG matching original profile (£3,400 × 4 = £13,600). Cornices: 96m original retained + lightly restored (£8,400 Pavilion Plaster); 6 ceiling roses cleaned + repaired. Pitch pine boards sanded + Junckers Strong satin lacquer (£3,800 supplied + installed). Internal wall insulation 80mm Kingspan K17 to party walls only (heritage front + rear retained breathable). Weeks 19–24 final fix + decoration + commissioning. Kitchen (Plain English bespoke shaker £42,000 supplied + installed; Calacatta Gold marble worktop + waterfall island £18,500; Crittall internal screen 4m × 2.4m £14,500 to broken-plan dining; integrated Sub-Zero + Wolf + Gaggenau appliances £28,500); 3 bathrooms (master en-suite with wet room + tadelakt feature wall; family bath + powder room; £62,000 total bathrooms). KNX commissioning + circadian programming over 3 weeks — Sound Servic technician + lighting designer programming scenes; client training. ASHP commissioning SCOP measured 3.84; MVHR commissioning 0.42 ACH continuous + measured 86% heat recovery; airtightness informal test 5.4 m³/h/m² @50Pa.

Outcome

EPC E (51) → B (84) — 33 SAP-point improvement (rare in heritage retention scope without EWI). KNX system fully commissioned + client-trained — circadian scheme working consistently 6+ months post-handover (client reports measurably better sleep + waking experience; tech-founder client running Google Fitbit study on family sleep quality pre/post — 18% sleep-onset improvement first 3 months). ASHP behind acoustic-treated yard fence — measured 32dB(A) at 1m from neighbour boundary (planning condition 45dB exceeded). 7 of 11 sash windows restored in situ — original glass preserved on study + 2 bedrooms; 4 replacements indistinguishable from originals from street. 96m original cornice + 6 ceiling roses + pitch-pine floors all preserved + featured. Property valuation: pre-renovation £1.05M; post-renovation £1.78M (+£730,000 on £425,000 spend net of BUS £7,500 grant — 175% gross ROI). Featured in Wallpaper* April 2027 Smart Home Spotlight + Cullen Lighting 2027 case-study portfolio + Sound Servic London KNX Case Study 2027. Wandsworth Society design award shortlist 2027. Builderr first KNX whole-house circadian project; Wandsworth borough portfolio 3rd case (after Tooting + Battersea); Balham SW12 first Builderr project in Bedford Hill area.