Grade II Georgian structural alteration with LBC + heritage propping

Brief

1832 Grade II listed Georgian terrace in Canonbury (N1), part of a Crown Estate-developed group on Canonbury Square. Owners — mid-career barristers, 8-year residents — wanted the cellular Georgian piano-nobile drawing-room layout reorganised: 5.6m structural opening through the spine wall between front and rear drawing rooms (creating a single 11.2m-long enfilade), and chimney-breast retention with internal cupboard reuse on both upper-floor bedrooms (Islington LBC route — removal refused at pre-app). No external alteration. Original 1832 mahogany pocket-shutter joinery to all 6 sash windows + original lime-plaster cornice + ceiling rose throughout all rooms must be retained and refurbished in situ.

Challenge

Grade II listed status means every structural element falls under LBC — Islington conservation officers reject chimney-breast removal universally in listed Canonbury stock and require heritage propping methodology for any RSJ work in 340mm Georgian solid-brick spine walls. Pre-app advice (£540 week 1) confirmed: chimney-breast removal refused, RSJ opening permitted subject to (a) heritage propping with timber needles + lime-mortar bedjoint preservation, (b) RSJ tucked above existing ceiling cornice line preserving Adam-style cornice + ceiling rose, (c) brick-by-brick reassembly of opening reveals in salvaged 1832 stock matched to original, (d) original mahogany pocket-shutter joinery refurbished and reinstated. 340mm solid-brick spine wall over 5.6m required 356×171 UB67 — heaviest residential RSJ in 8 years of Builderr work. SE Heyne Tillett Steel (heritage specialist). 4 Party Wall awards (left + right + above + below — the property is mid-terrace of 6 listed houses, each shares boundary with adjacent listed listed nuisance value). LBC + building control + Party Wall parallel determination. Family in residence weeks 1–8 (consents phase + propping); decanted to rental flat weeks 9–16 (steel + reinstatement phase).

Solution

Pre-build 14 weeks: LBC + full planning combined application week 2; Heyne Tillett Steel SE calculation pack £2,800 (heritage methodology) week 3; LBC determined week 12 first-time approved with 4 conditions — heritage propping methodology approved, RSJ tucked above cornice line, salvaged-brick reassembly, original joinery retention; Party Wall surveyor Peter Barry served 4 notices week 4, 4 awards in hand week 12; Islington building control Full Plans submitted week 6, approved week 10. 16-week site: weeks 1–2 careful removal and labelling of original 1832 mahogany pocket-shutter joinery (5 sashes) for offsite refurbishment at Ventrolla workshop; weeks 3–5 heritage propping — timber needles at 450mm centres (closer than Victorian work given Georgian 340mm spine), 100mm × 100mm timber sole plates over lime-mortar bedjoints (never direct onto brick), 8 acrows on 200mm-square solepieces to floors above; weeks 6–8 careful demolition of 5.6m spine wall section, brick-by-brick removal preserving 312 original 1832 yellow stock bricks for reveal reassembly, lime-plaster cornice line preserved within 50mm of demolition; weeks 9–10 356×171 UB67 craned in (road closure permit £640) and installed flush with cornice line, bearing onto Class B engineering-brick padstones in 3:1 sand-cement on both party walls (Party Wall awards permitted padstone landing with above + below neighbours notified); weeks 11–12 brick-by-brick reassembly of opening reveals in salvaged 1832 stock bedded in NHL 3.5 lime mortar, mahogany pocket-shutter joinery reinstated to refurbished sashes; weeks 13–14 lime-plaster making-good (Hayles & Howe specialist heritage plasterer £4,200 for 12m run-in-situ cornice replication to bridge demolition line) + original Adam-style ceiling rose retained intact; weeks 15–16 chimney-breast cupboard joinery built into both upper-floor bedrooms (bespoke painted-MDF cupboards with shaker-frame doors — LBC condition 4 reversibility), F&B paint throughout (Pointing, Dimity, French Gray), original cornice + ceiling rose + dado + skirting all retained. LBC sign-off inspection week 16 — Islington conservation officer signed off without remediation.

Outcome

Site completed week 16, on programme. 5.6m structural opening through 340mm Georgian solid-brick spine wall achieved with the RSJ tucked flush above the original 1832 Adam-style cornice line — no downstand, single continuous cornice from front bay to rear drawing room. 312 of 312 original 1832 yellow stock bricks salvaged and reassembled into opening reveals — Islington conservation officer described the reassembly in the LBC sign-off as 'an exemplary heritage propping and reveal-reassembly methodology, demonstrating exactly the kind of skilled craft heritage structural work that Listed Building Consent is designed to encourage'. Original mahogany pocket-shutter joinery (5 sashes) refurbished by Ventrolla and reinstated. Twin chimney breasts retained per LBC condition with internal cupboard reuse — bespoke shaker-frame painted-MDF joinery that is fully reversible (LBC condition 4). 12m of run-in-situ cornice replication by Hayles & Howe bridges the demolition line invisibly. EPC unchanged (no external fabric change). Resale-equivalent uplift £325k on £96.5k spend = 237% gross ROI — top-decile for a structural-alterations-only scope in a Grade II Canonbury house. First Builderr 356-series RSJ in 8 years (heaviest residential beam to date) + first Crown Estate-developed Georgian listed structural opening + first Hayles & Howe heritage-cornice bridge over an RSJ-line + Islington conservation officer 'exemplary heritage propping and reveal-reassembly methodology' commendation in LBC sign-off letter cited in Builderr's next 3 Canonbury Square pre-app submissions.