Double-storey side extension + loft conversion, Winchmore Hill

Brief

A 1934 semi-detached house on a leafy street in Winchmore Hill, Enfield — N21, not in a conservation area. The property: 96m² original (3 bedrooms, 1 bathroom, narrow corridor kitchen, integrated half-side garage). The brief: maximum value-add renovation transforming the property from a typical 3-bed inter-war semi into a 4-bed-2-bath modern family home. Three interventions: (1) double-storey side extension over and replacing the integrated garage; (2) hip-to-gable loft conversion with rear dormer creating master suite; (3) full ground-floor reconfiguration to open-plan kitchen-diner-utility. Combined effect: floor area 96m² → 175m²; bedrooms 3 → 4; bathrooms 1 → 2. The clients had a fixed budget of £150,000 (achieved £145,000 outturn) and a target sale price of £950,000 within 3 years.

Challenge

Multi-intervention scope required careful sequencing. Side extension over the existing garage required structural intervention — original garage walls were single-skin breeze block (no foundations adequate for first-floor loading); demolition and rebuild on new strip foundations to 0.9m depth on London Clay. Mock-Tudor first-floor gable: planning required the new first-floor extension to match the existing host property's mock-Tudor character — sourcing matching timber and arranging custom render finish required specialist craftsman. Hip-to-gable loft: roof structure had to be re-formed (original 1934 hip removed, new gable end in matching brick); rear dormer added under PD. Ground-floor open-plan: original layout had three separate rooms with one identified as load-bearing supporting first-floor wall above. Structural engineer specified 4.5m UB 254×146×31 steel beam with twin pad-stones. Party Wall: Section 6 notice served to attached neighbour; excavation within 3m of attached neighbour's foundation; Agreed Surveyor route; Award sealed in 4 weeks.

Solution

Planning: full planning application (side extension over former garage triggers full planning per Enfield local plan); granted 8 weeks first-time. Loft conversion separately progressed under Prior Approval. Structural: side extension ground-floor (3m × 5m) on strip foundations 0.9m depth, cavity brick to red-brick match (sourced via Ibstock); first-floor (3m × 5m) timber-frame construction with red brick outer leaf + mock-Tudor render to gable; 4.5m UB 254×146×31 steel beam internal opening for ground-floor. Loft: hip-to-gable on the attached-neighbour-side; rear dormer (5m × 3m, EPDM flat roof, 3 Velux); new staircase rising over existing landing. Ground floor reconfiguration: 4.5m UB steel installed; original wall demolished; existing 35m² of three rooms + new 15m² side extension = 50m² combined open-plan kitchen-diner-utility. Mock-Tudor restoration: salvage timber sourced from a Hertfordshire demolition (matched 1930s oak boards); custom render finish in matching colour (Crown Marble Finish + iron oxide pigment); result: indistinguishable from original from street view. Sash windows on host property: 6 windows restored with slim DG retrofit; new side-extension windows specified as matching profile. Master suite (loft): 16m² master bedroom with rear-dormer dual-aspect glazing; 5m² en-suite (compact wet-room style with frameless shower); 4m² walk-in wardrobe (built-in oak veneer joinery, full ceiling height). Kitchen: 6m galley arrangement + 3m island in painted-MDF Farrow & Ball Card Room Green with brass handles. EV charger: 7kW Hypervolt on forecourt.

Outcome

Floor area added: 79m² (side extension ground 15m² + side extension first-floor 15m² + loft 24m² + reconfigured ground-floor footprint gain 25m² net). Property: 96m² → 175m² — 82% increase. Bedrooms: 3 → 4. Bathrooms: 1 → 2. EPC: D (61) → B (84) — full rewire and new combi boiler; CWI; loft insulation 270mm; double glazing throughout. Build 18 weeks. Enfield Building Control completion certificate issued at week 19. Estate agent post-completion valuation £935,000 — within £15,000 of client's target. Original purchase (2021) £675,000 + £145,000 spend = £820,000 invested; comparable post-renovation 4-bed semi in Winchmore Hill sold for £945,000 same month.