Carlton Lodge, Belgravia SW1X
A high-spec penthouse duplex transformation in a listed urban context: full internal rebuild, roof reconstruction with structural steel, new services and premium fit-out for multi-unit handover.
Penthouse Duplex in a Listed Setting
Carlton Lodge occupies a prime Belgravia position within a Grade II listed building envelope. The brief was ambitious: transform the underperforming top two floors into a premium duplex penthouse while simultaneously refurbishing four adjacent apartments — all without compromising the listed building fabric or disrupting the occupied units below.
The most significant intervention was a complete roof reconstruction using structural steel to create the headroom and spatial quality expected at this price point. New steel portal frames were craned into position during carefully coordinated weekend lifts, with the existing roof structure stripped back to facilitate the new geometry while maintaining the external roofline profile required by the listing.
The interior design programme demanded the highest specification throughout: engineered oak flooring, natural stone bathrooms, bespoke kitchen cabinetry with integrated Gaggenau appliances, and a full smart home system. Every material selection was made to reflect the Belgravia standard while delivering contemporary living for the international buyer market.
Quality control across five overlapping apartment scopes required dedicated site management and a rigorous inspection regime. The staged handover programme ensured each unit was completed to snagging standard before the next was released, minimising defects and maintaining the premium quality expected at this level.
7-Stage Project Timeline
From listed building coordination through to staged handover, every phase of this 11-month programme was managed to the highest Belgravia standards.
Initial Brief & Site Survey
Detailed assessment of the existing penthouse layout and roof structure within the listed building context. Our survey identified the structural constraints of the existing timber roof and mapped party wall conditions with adjoining properties. The client’s brief centred on creating a flagship duplex with four additional apartments for the investor portfolio.
Concept Design
Two concept schemes were developed for the duplex layout, exploring different approaches to the internal staircase positioning and the relationship between the principal entertaining floor and the upper bedroom level. The selected scheme placed a dramatic double-height void at the heart of the duplex with a feature staircase in bronze and glass.
Planning & Approvals
Listed building consent coordination required close engagement with the Westminster conservation officer. A heritage impact assessment demonstrated that the roof reconstruction would maintain the external profile while significantly improving the internal spatial quality. The application was supported by detailed visualisations showing the before-and-after roofline from key viewpoints.
Technical Design
The structural steel package was designed in detail, with connection drawings for every node point and a sequenced erection methodology that minimised the period the building was open to weather. M&E design addressed the challenge of routing new services through a listed building without damaging original fabric, using concealed bulkheads and raised floor zones.
Construction & Structure
Strip-out proceeded carefully under archaeological watching brief conditions required by the listing. The steel package was craned in during two weekend operations, with the new portal frames bolted into position before the temporary weatherproofing was removed. Demolition of the existing internal layouts across all five units ran in parallel once the structural frame was secured.
Fit-Out & Finishing
The duplex fit-out demanded exceptional craftsmanship: the bronze-and-glass staircase was fabricated off-site and installed in three sections, engineered oak flooring was laid throughout, and natural stone was fitted in all five bathrooms. Each apartment received its own bespoke kitchen and the smart home system was commissioned across all units simultaneously.
Handover & Aftercare
A staged handover programme released units sequentially: the four apartments were completed first, followed by the flagship duplex. Each unit underwent independent snagging by the client’s representative, a professional deep clean, and formal handover with all compliance documentation, EPC certificates, and warranty packs. Our 12-month aftercare programme covers all five units.
What We Delivered
Penthouse Duplex Conversion
Complete strip-out and reconfiguration of the top two floors into a premium duplex with double-height void, feature staircase and panoramic terrace access.
Structural Roof Rebuild
Full roof reconstruction with structural steel portal frames to create the headroom and daylight required for premium penthouse living, maintaining the listed external profile.
4 Apartment Refurbishments
Simultaneous refurbishment of four adjacent apartments with new kitchens, bathrooms, flooring and bespoke joinery packages to investment-grade specification.
Full Services Renewal
Complete electrical and plumbing renewal with updated compliance strategy, smart home integration and concealed services routing through the listed building fabric.
Investment Breakdown
How the £1.9M–£2.4M budget was allocated across the major work packages.
Problems We Solved
Listed Building Constraints
Working within a Grade II listed envelope where every intervention required conservation officer approval and original fabric preservation.
Engaged heritage consultant from day one. Archaeological watching brief during strip-out. All interventions designed to be reversible where required by the listing.
Structural Steel in a Live Building
Craning structural steel into a residential building in central Belgravia with occupied units below and restricted road access.
Weekend crane operations with advance resident notification. Steel delivered in manageable sections with bolted connections to minimise on-site welding noise.
Premium Finish Quality
Integrating premium finishes with services routes and structural constraints across five overlapping apartment scopes.
Dedicated fit-out manager for each unit with daily quality inspections. Mock-up rooms approved before full installation. Concealed services zones designed into every layout.
Multi-Unit Coordination
Delivering quality control across the duplex and four apartments simultaneously without trades interfering across units.
Staggered fit-out programme with dedicated trade teams for each unit. Staged handover ensured each apartment met snagging standard before the next was released.
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