Use class + planning route + fees + timeline
Use Classes Order 1987 (amended): Class C3 — single dwelling, single person/family or up to 6 unrelated as single household. Class C4 — small HMO 3–6 unrelated sharing facilities. Sui generis — large HMO 7+ unrelated, no defined class. Conversion routes: (1) C3 → C4: permitted development under GPDO 2015 Class L outside Article 4 — no planning, just HMO licence ([[hmo-licensing-london-cost-and-process]]). Inside Article 4 = full planning ([[article-4-hmo-london-which-boroughs]]). (2) C3/C4 → sui generis (7+): full planning always. Fee £462 change of use + £462–£675 with extensions = £924–£1,137. Architect + planning statement + management + amenity + acoustic/parking/transport £2,400–£8,500. Pre-app £540–£1,200 (essential for sui generis). Pre-app + submission 8–14 weeks; validation 1–2 weeks; consultation 21 days; decision 8 weeks (or 13 for major); committee = 16–22 weeks. Section 106 on large HMO: £8,000–£25,000 per net additional bedspace; £3,500–£12,000 public realm + transport; car-free condition (no permit eligibility); cycle parking 1 per occupant. CIL: £45–£180/m² on net additional floorspace per borough.
Refusal triggers + mitigation + design standards + Builderr approach
Common refusal triggers London 2026: (1) HMO saturation — 10–20% concentration thresholds per defined area; Newham, Croydon, Brent, Waltham Forest publish saturation maps. (2) Loss of family housing — target small HMO from already-converted flat or ex-bedsit. (3) Amenity harm — noise, refuse, 24/7 comings + goings, parking pressure. Mitigation: acoustic glazing, 24/7 manager, refuse storage + collection, car-free + cycle provision, ASB management plan. (4) Parking/transport — PTAL 4+, cycle 1.5–2 per occupant. (5) Character harm — discrete external, no signage, original entrance + garden retained, comparator HMOs evidenced. (6) Fire safety + amenity below standard ([[hmo-fire-safety-compliance-london]], [[hmo-amenity-standards-london]], [[minimum-room-sizes-hmo-london-2026]]). Mitigation: design 10–15% above minimum, full fire engineer report (Hoare Lea, Tenos, Olsson Fire), sprinkler retrofit on 3+ storey, FD60S + L1 alarm. (7) Insufficient management plan — named manager, 24/7 contact, ARLA/Propertymark agent, tenancy template. Builderr design + planning approach: pre-app advice always; saturation + amenity desktop; design exceeding HMO Standards 2018 by 10–15%; fire engineer report for 3+ storey; acoustic glazing; cycle + refuse store in front garden behind hedging/timber screen; named manager + ARLA agent appointment evidence; pre-consultation with neighbours + recorded responses. Result: approval 65–75% in Article 4 (vs LPA average 35–45%) + minimal conditions (8–15 vs 18–30) + faster determination (avg 11 weeks vs 16). Typical 6-bed C3→sui generis project total £125,000–£195,000. Yield: 6 × £950–£1,400/month = £68,400–£100,800/year gross; £8,500–£14,500 management + maintenance + insurance + voids; £8,500–£18,500 mortgage + Section 24 tax on financing; net £35,000–£62,000/year. Yield 6.5–9.5% gross vs single-let 4.5–5.5% London average. See [[buy-to-let-renovation-budget-london]].
