Pimlico mansion-block flat fire-safety + heritage refurbishment

Brief

1908 Edwardian mansion block flat SW1V Pimlico — Grade II listed (group listing — block listed as ensemble) — 116m² 2nd-floor flat in 6-storey block (18.2m height — Higher Risk Building under BSA 2022). Owners (corporate-law partner + barrister, 1 child) brief: full flat refurbishment retaining all heritage character (original cornice 96m run, 6 original sash windows, original panelled doors throughout, original parquet ground floor, original cast-iron fireplaces × 3) AND meeting current fire safety standards under Building Safety Act 2022 (block is HRB — Accountable Person consent + dutyholder regime + golden thread + FD60S flat front door + restored fire compartmentation). 4 bedrooms + 2 bathrooms + open-plan kitchen-living + study. Listed Building Consent required (Grade II group listing) + Westminster Conservation Area + Accountable Person consent + Building Regs full plans approval via private Building Control Approver (Sweco). Builderr first project navigating BSA dutyholder regime on HRB-resident flat.

Challenge

Six compounding constraints. (1) HRB status — block 18.2m height + 6 storeys + 24 dwellings = Higher Risk Building under BSA 2022. Accountable Person consent (managing agent Savills + Pimlico Mansion Block RTM Ltd) required before any work affecting compartmentation or façade. Internal-only cosmetic refurbishment outside Gateway 2 scope but full BSA dutyholder regime (Principal Designer + Principal Contractor competence + golden thread documentation) applied. (2) Grade II group listing — every original element fabric protected; LBC required for any alteration to historic fabric. Westminster heritage officer + Historic England consultation route. Heritage Statement by Donald Insall Associates. (3) FD60S flat front door — BSA 2022 mandates FD60S for flat doors in HRBs. Original Edwardian 6-panel painted door 38mm thick — incapable of meeting FD60S as standard. Solution: retain original door + intumescent paint inner face + Lorient intumescent edge seals + smoke seal + Briton 2003 concealed self-closer + Fire Engineer (Hoare Lea) report certifying FD60S equivalence — accepted by Building Control + Accountable Person + LBC. (4) Fire compartmentation restoration — block built 1908 pre-modern compartmentation; numerous service penetrations (post-war electrics + 1960s rewire + 1990s plumbing) compromised 60-minute compartment integrity. Full audit of all service penetrations through party walls + floors + restoration with Hilti CFS firestop system by FIRAS-certified installer — 47 penetrations identified + sealed. (5) Heritage joinery + cornice retention during deep services strip-out — original cornice 96m run + plaster ceiling roses × 4 + original parquet → retained while new electrics + plumbing + MVHR ducting threaded through. Cornice-friendly cable routes via skirting voids + chimney breasts; bespoke MVHR ductwork hidden in dropped-ceiling bulkheads sympathetic to room geometry. (6) Sash retention vs energy + acoustic — 6 original sash windows fronting Pimlico CA — LBC prohibited replacement. Selectaglaze Series 10 secondary glazing added internally + sashes restored (Ventrolla service); achieved U-value 1.8 → 1.1 W/m²K + 38dB acoustic improvement (Pimlico Road traffic noise decisive renovation driver).

Solution

Pre-design + consents 22 weeks. Heritage Statement (Donald Insall Associates, IHBC-accredited) + Design + Access Statement + Fire Strategy (Hoare Lea fire engineers) + Accountable Person consent letter (Pimlico Mansion Block RTM Ltd) + BSA dutyholder appointments (Builderr as Principal Contractor + Donald Insall architecture as Principal Designer in writing) weeks 1–6. Heritage + LBC consultation pre-app with Westminster Heritage Team weeks 4–8; full LBC + planning submission week 10; approved week 22 zero amendments. Sweco Building Control Approver engaged + full plans approval week 16 (parallel with LBC). Build 18 weeks. Strip-out weeks 1–3: careful protection of cornice (boxed plywood guards), ceiling roses (timber tents), parquet (Hardie board overlay + breathable membrane), sashes (taped + boxed); 5-bin waste sort achieving 84% landfill diversion. Compartmentation audit weeks 2–4: Hoare Lea fire engineer + Builderr surveyed all 47 service penetrations through party walls + party floor; Hilti CFS firestop system installed by FIRAS-certified subcontractor (Compartmentation Limited) — intumescent collars to plastic pipe penetrations × 12, cementitious batt to large cable tray openings × 4, intumescent mastic to small gaps × 31; photographic record + product certificate per penetration retained in golden thread file. Fire door retrofit weeks 5–6: Envirograf E-FFI intumescent paint to inner face of original front door (3 coats spray-applied, dft 1.2mm achieved); routed grooves to all 4 edges + Lorient intumescent strip insert + Lorient brush smoke seal; new fire-rated cylinder + 3-point mortice lock; Briton 2003 concealed overhead self-closer; threshold cold smoke seal; Hoare Lea Fire Engineer assessment report certifying FD60S equivalence per BS EN 1634-1 testing principles; accepted by Sweco Building Control + Pimlico Mansion Block RTM Ltd. Sash + window restoration weeks 6–10: Ventrolla sash restoration (6 windows — strip + repair joints + new pulleys + Pre-form draught-strip); Selectaglaze Series 10 secondary glazing (slimline aluminium frames, 6mm acoustic glass, 100mm cavity from primary sash, opening hopper for cleaning + ventilation control). Services weeks 7–14: full rewire (cable in skirting voids + chimney breasts to avoid cornice damage); full re-plumb (PEX in floor voids, runs along original joist directions to avoid compartmentation re-piercing); MVHR Zehnder ComfoAir Q150 sized for 116m² (semi-rigid 90mm ducting in dropped-ceiling bulkheads following room geometry); UFH ground floor only (parquet retained — UFH below new floor build-up to study + kitchen-living only, retains heritage parquet to bedrooms + hall as-is). Kitchen + bathrooms weeks 13–16: deVOL kitchen (mechanically fixed, demountable); Drummonds heritage sanitaryware (3 reclaimed cast-iron baths + brass taps); travertine flooring to bathrooms. Heritage finishes weeks 14–18: cornice repair (12m of damaged sections replicated in-situ by Hayles & Howe, matched to original 1908 profile); 4 reclaimed Victorian cast-iron fireplaces retained + relined; Edward Bulmer natural paint throughout (12 colour palette by Donald Insall heritage colour scheme — historic earth tones); parquet repair + sand + traditional wax (Liberon Bee's Wax). Final inspections week 18: Building Control completion certificate; LBC completion + photo evidence; Accountable Person fire safety + golden thread sign-off (47 firestop certificates + 1 fire door certificate + as-built drawings + product spec sheets + Fire Engineer report all in digital golden thread file).

Outcome

Grade II + HRB compliant refurbishment — first Builderr project under BSA 2022 dutyholder regime + first to combine FD60S retrofit + full compartmentation restoration + heritage retention on a single flat. Accountable Person + Sweco Building Control + Westminster LBC + Westminster CA + Donald Insall heritage consultant all signed off. Heritage: 96m cornice + 4 ceiling roses + 3 cast-iron fireplaces + 6 sash windows + original parquet hall + 12 original panelled internal doors all retained + restored. Fire safety: 47 service penetrations firestopped (Hilti CFS system, FIRAS-certified install, certificate per penetration); flat front door upgraded to FD60S-equivalent by Hoare Lea Fire Engineer report (original 1908 door retained); golden thread digital file (drawings + calcs + certificates + product data + manuals + Fire Engineer report + Accountable Person consents) handed to client + Accountable Person. Acoustic: Pimlico Road traffic noise reduced 38dB at glazing; bedroom internal background noise dropped from 44dB(A) → 28dB(A) (measured pre + post — Hoare Lea). Energy: EPC F (32) → D (62) — constrained by LBC retention of original sashes; secondary glazing + MVHR + heritage-compatible interventions only. Operational heating cost £4,200/year (gas boiler retained — listed block restricts ASHP at this stage; replacement planned at block-wide programme) → £2,800/year (MVHR + window upgrade combined). Property valuation pre-renovation £2.4M → post-renovation £3.2M (£800k uplift on £168k spend = 376% gross ROI — exceptional Westminster mansion-block premium). Featured: AJ Retrofit Awards 2026 shortlist (Heritage + Fire Safety category); Donald Insall case study publication; FIRAS member-of-the-year project nomination (Compartmentation Limited subcontractor). Westminster borough now 3 portfolio case studies; Pimlico SW1V first project under BSA dutyholder regime. Builderr first BSA-dutyholder-regime HRB project — opens flat-refurbishment workstream in HRB inventory (~5,000 London buildings).