Edwardian semi + rainwater harvesting + microcement kitchen, Wanstead E11

Brief

1908 Edwardian semi-detached E11 Wanstead — 142m² over two storeys, 280m² plot with mature south-facing rear garden 180m², original sash windows (12 of 14 surviving), original cornice + ceiling roses in 4 rooms, original Minton encaustic hallway tile, pitch-pine floors. Wanstead Conservation Area (sympathetic — not heavy enforcement). Owners (sustainable architect + university lecturer + 2 children) brief: environmentally focused renovation — 6,000L rainwater harvesting (target 60% mains water reduction for WC + washing + garden), microcement kitchen floor + dining (continuous seamless concrete-look), ASHP + MVHR retrofit, full sash restoration, side-return + loft conversion. Brief explicit: BREEAM Domestic Refurbishment Excellent target + low embodied carbon material choices (sheep wool insulation, lime plaster, Belgian Mortex microcement, FSC oak, low-VOC Edward Bulmer paints throughout). Budget £295,000 (£2,080/m²). Wanstead CA — sash restoration + sympathetic material spec required. Rainwater system Building Regs + Water Regs compliance.

Challenge

Five interlinked constraints. (1) BREEAM Domestic Refurbishment Excellent target — comprehensive scope including water (rainwater harvesting + WC + washing + garden), energy (ASHP + MVHR + thermal upgrade), materials (sheep wool insulation + lime plaster + low-embodied-carbon), waste (90% construction waste recycling + reuse), pollution (low-VOC + zero CFC + heat-recovery), health (IAQ + ventilation + daylight). Coordinated by BREEAM assessor (Sustainable Homes) from RIBA Stage 2. (2) Rainwater system — 6,000L Klargester FlatPak buried rear garden (London clay subsoil + anti-flotation collar + 1.8m dig + reinstate £2,400); dual-piped distribution within house (separate non-potable to 3 WCs + washing machine + outside tap, mains-isolated by air gap + clearly labelled); Water Regs notified install (Thames Water Section 5 compliance); pump + filter + first-flush diverter + mains backup. (3) Microcement kitchen + dining — Belgian Mortex (premium microcement, Marius Aurenti UK importer) applied over original concrete sub-floor by Italian-trained specialist (Pandomo UK approved); 4–7 day application + 28 day cure before furniture; £18,500 supply + apply 32m²; seamless extension into adjacent dining; high quality finish requires meticulous substrate prep. (4) Sheep wool insulation throughout — Black Mountain Insulation 100mm loft + 50mm internal wall (party wall only); breathable + carbon-sequestering + biodegradable but 60% more expensive than mineral wool (£14,500 supply + install vs ~£8,500 mineral wool). (5) Sash restoration — 12 of 14 surviving sash windows restored in situ (re-corded + Histoglass slim DG conversion preserving original Crown glass on stairs + 2 reception bays); 2 replacements (rear elevation Mumford & Wood Conservation Range slim DG). Conservation Area officer approval; sample window approved week 0.

Solution

Pre-design 18 weeks. Architect (CMS Studio — sustainable architecture specialist) RIBA Stage 4 with BREEAM assessor (Sustainable Homes) from Stage 2; structural engineer; M&E consultant (ASHP + MVHR + rainwater); materials specifier; Wanstead CA pre-application secured for sash restoration spec + ASHP siting + microcement. Build 22 weeks. Weeks 1–4 strip-out + heritage protection. 1990s kitchen + bathrooms + carpet removed. Pitch-pine boards numbered + lifted. Cornices + ceiling roses + Minton tile floors protected with PE + plywood enclosure. Strict construction waste segregation (BREEAM Wst02 — 90% target): timber, plasterboard, brick + concrete, metal, mixed waste streamed to separate skips; 92% diversion achieved per Reconomy report. Weeks 5–10 structural + groundworks. Side-return foundation (mini-pile to protect mature lime tree TPO — £8,500 mini-pile vs £4,200 strip foundation premium for TPO protection). Loft conversion structural — L-shape dormer + hip-to-gable. Rear garden 6,000L Klargester FlatPak tank install — Thames Water Section 5 notification + Water Regs compliance; dig + anti-flotation collar + reinstate £2,400. Cement-bound base + tank install + ducting to 4 downpipe diverters + 32mm MDPE pipe to plant cupboard in utility. Weeks 11–14 first-fix services. ASHP first-fix — Vaillant aroTHERM Plus 7kW external rear flank (CA-approved siting) + 250L cylinder utility cupboard; flow 45°C; 14 oversized Bisque Classic 3-Column matt black radiators (50–70% larger than legacy single-panel). MVHR first-fix Vent-Axia Sentinel Kinetic FH 200 in loft plant; 9 supply + 7 extract; semi-rigid 90mm radial ducting. Rainwater install: pump + filter + first-flush diverter + mains backup + dual-piped distribution to 3 WCs + washing machine + outside tap (all clearly colour-coded non-potable + labelled per Water Regs). Standard electrics: 16-way RCBO CU; 12 lighting circuits; EV charger 7kW Zappi V2 with smart load management (front driveway). Weeks 15–18 thermal + plaster + heritage restoration. Sheep wool insulation: 100mm Black Mountain in loft (300m²) + 50mm Black Mountain IWI party wall only (45m²); heritage front + rear breathable construction retained. Lime plaster (Lime Stuff) over IWI + repair to existing lime + sand plaster; £45/m² premium vs gypsum. Sash window restoration: 12 originals in situ by Ventrolla (slim 8mm Histoglass DG conversion £1,400 × 12 = £16,800); 2 rear replacements Mumford & Wood Conservation Range £2,800 × 2 = £5,600. Cornice restoration: 78m surviving original lightly restored by Pavilion Plaster (£6,400); 4 ceiling roses cleaned. Minton hallway tile restored (gentle clean + 2 missing tiles sourced from Lassco £85 × 2 + relaid £450). Weeks 19–22 final fix + microcement + decoration. Kitchen + dining microcement install (4 days application + 28-day cure before second-fix — phased to keep family out of cure zone during weeks 19–20). Plain English shaker kitchen (£32,000 supplied + installed); reclaimed elm worktop (£8,500 — Lassco reclaimed beam slabbed + planed); brass tap + handles (Devol Aged Brass). 3 bathrooms (master en-suite wet room with Mortex microcement floor + tadelakt feature wall; family bath; powder room). Decoration: Edward Bulmer Natural Paint throughout (all rooms — plant-based pigment + linseed oil + chalk base; zero-VOC; £45/L premium spec); heritage palette (Wevet + Cornforth White + Edwardian Green + Library Red). BREEAM final assessment — Excellent rating achieved (post-construction certified rating 75.2 of 100 points; threshold 70+ Excellent).

Outcome

BREEAM Domestic Refurbishment Excellent certified (75.2 points / 100; threshold 70+; first Builderr BREEAM Excellent retrofit). EPC F (37) → B (82) — 45-point SAP improvement (exceptional in heritage retention scope). Rainwater system performing: 62% mains water reduction for WC + washing + garden first 6 months operation (target 60% met + exceeded); estimated annual water saving 38,000L = £56/year on water + £42/year on sewerage. Rainwater audited monthly via Thames Water consumption data + dedicated meter on dual-pipe distribution. Sheep wool + lime plaster spec: monitored IAQ shows CO2 average 580 ppm + RH 48% stable + TVOC <180 µg/m³ (very low — Edward Bulmer paints driving). 12 of 14 sash windows restored in situ + original Crown glass preserved on stairs + 2 reception bays — CA officer sign-off zero amendments. Microcement floor performing — 6-month wear assessment by Pandomo UK shows zero cracking + uniform aesthetic. Property valuation: pre-renovation £765,000; post-renovation £1.18M (+£415,000 on £295,000 spend net of grants £7,500 BUS — 144% gross ROI). Premium for sustainability spec evident in valuation (RICS surveyor specifically cited BREEAM Excellent + rainwater + ASHP + heritage retention as 'all four together' uplift drivers). Featured in BREEAM Awards 2027 (Residential Refurbishment shortlist) + Wanstead Conservation Society award + Sustainable Architecture magazine July 2027 issue. Builderr first BREEAM Excellent retrofit; Redbridge borough portfolio 2nd case (after Seven Kings); Wanstead E11 first Builderr project in Wanstead CA.