Wraparound side-rear extension + dormer loft, Romford

Brief

A 1962 brick-and-render semi-detached in Gidea Park, Romford — RM2, not in a conservation area, PD rights intact (Havering is one of London's most PD-friendly outer boroughs). The clients (couple with three children) had outgrown the 96m² 3-bed layout and wanted a 4-bed family home with a large kitchen-diner. The 3m side return and 9m rear garden depth allowed a wraparound single-storey extension plus a rear dormer loft conversion as a combined project. Total budget: £168,000. Havering borough first case study for the Builderr portfolio.

Challenge

Three constraints shaped the design. (1) PD wraparound compliance — combined side and rear elements straddle two PD classes (Class A side + Class A rear with Larger Home Extension Prior Approval). Builderr submitted a single Lawful Development Certificate plus Prior Approval for the rear 4.8m projection. LDC granted at 8 weeks; Prior Approval granted at 7 weeks (no neighbour objections during 21-day consultation). (2) Drainage and soakaways — London Clay site with BRE Digest 365 infiltration rate of 8mm/hour (borderline acceptable). Building Control accepted a modified soakaway with overflow to the existing surface-water drain into the Havering Council adopted highway drain. (3) Loft head height — existing loft ridge 2.55m, eaves 1.6m — marginal for habitable conversion. Solution: rear dormer with 2.4m internal head height across the full new dormer footprint (8m × 4m). Dormer volume 80m³ exceeded the 50m³ Class B PD allowance for a semi, so full planning was required (granted at 9 weeks). Existing 1980s side-return lean-to had an asbestos-cement roof requiring HSE-licensed abatement (£2,800 specialist contractor budget line).

Solution

Phased programme: family in residence weeks 1–8 (loft only, accessed via external scaffold staircase), then vacated weeks 9–20 (ground-floor wraparound + first-floor remodel). Phase 1 — loft: existing roof opened internally, new 175mm joist floor with acoustic underlay; rear dormer 8m × 4m flat-roof timber-frame construction with EPDM warm deck and zinc cladding to front face; 2× Velux GGL UK10 to front pitched slope; new staircase from first-floor landing (winder-foot configuration); master 16m² + en-suite 5m² + walk-in wardrobe 3m². Phase 2 — wraparound: 1980s asbestos-roofed lean-to abated by HSE-licensed contractor; new strip footings 600mm × 1.0m on London Clay; 178×102 UB steel beam at junction of existing rear wall and new extension; 38m² ground-floor addition (kitchen 18m², diner 12m², family/snug 8m²) open-plan with 4.2m × 2.1m Reynaers CF 77 bifolds (anthracite grey, flush threshold) and 1.5m × 1.5m Glazing Vision roof lantern above the dining table; integrated boot room (3m²) off the side entrance from the driveway. First-floor remodel: ensuite added to second bedroom; family bathroom refurbished; airing cupboard relocated. Heating: 2008 Worcester combi decommissioned; new Vaillant ecoTEC plus 38kW combi installed in utility room; 14 new radiators (heat-pump-ready sized for 50°C flow); wet UFH to ground-floor extension only.

Outcome

Floor area added: 62m² (38m² wraparound ground floor + 24m² dormer loft). Property uplifted from 96m² 3-bed/1-bath to 158m² 4-bed/2.5-bath. Side-return 1980s lean-to (16m² of low-quality, asbestos-roofed cold space) demolished and replaced; net habitable floor area gain 46m² after demolition. EPC: D (62) → C (76) — new extension to Part L 2025; loft insulation top-up to 350mm; new boiler. Build delivered in 20 weeks within programme (8 weeks Phase 1 + 12 weeks Phase 2); final spend £172,400 against £168,000 budget (2.6% over due to asbestos abatement contingency). Romford market: pre-renovation valuation £475,000; post-renovation £685,000 (£210,000 gross value uplift on £172,400 build cost — 22% ROI). Havering Council Building Control completion certificate issued at week 21.