Belsize Park Gardens, NW3
Five-storey period-home transformation combining basement conversion, rear extension and loft works with a complete interior refurbishment package in a high-value NW3 conservation context.
A Whole-House Transformation in Conservation Context
The owners of this five-storey Victorian townhouse on Belsize Park Gardens approached us with an ambitious vision: to completely reimagine their home from basement to roofline while preserving the period character that makes NW3 one of London's most desirable conservation areas. The property had been incrementally updated over decades, resulting in a patchwork of styles and compromised spatial flow across all five levels.
Our design team proposed a comprehensive strategy that would unlock over 40% additional living space through a basement conversion, a rear extension at garden level, and a sympathetic loft conversion — all within Camden Council's strict conservation area guidelines. Every intervention was designed to complement the original Victorian architecture while delivering a thoroughly modern family home.
The construction programme required careful sequencing to manage the complexity of working simultaneously across five floors. Structural works began from the basement up, with underpinning and tanking completed before the ground-floor extension steelwork was installed. The loft conversion followed, with new dormers designed to match the existing roofline profile along the terrace.
The result is a seamlessly integrated home where original cornicing, ceiling roses and timber panelling sit alongside underfloor heating, a whole-house ventilation system and a contemporary open-plan kitchen-dining space. The property valuation increased substantially, reflecting both the additional square footage and the quality of execution throughout.
7-Stage Project Timeline
From initial brief through to handover, every stage of this 16-month programme was carefully planned to deliver a seamless whole-house transformation.
Initial Brief & Site Survey
The clients outlined their vision for a comprehensive family home transformation. Our team conducted a full measured survey of the five-storey property, identified key structural constraints including party wall conditions with both adjoining properties, and assessed the basement for conversion potential including groundwater risk.
Concept Design
Three concept options were developed exploring different approaches to the basement layout, rear extension form and loft configuration. The clients selected a scheme that maximised the open-plan lower ground floor while creating a master suite in the loft with a juliet balcony overlooking the gardens. Material palettes drew from the Victorian context — reclaimed timber, handmade tiles and brass ironmongery.
Planning & Approvals
Working within Camden's conservation area required a heritage impact assessment and careful pre-application engagement with the planning officer. The rear extension was designed to sit below the parapet line, and loft dormers were set back to minimise street-level visibility. Planning approval was secured without committee referral thanks to thorough pre-application work.
Technical Design
The full technical package covered structural calculations for the basement underpinning, extension steelwork and loft dormers, along with M&E design for underfloor heating, whole-house ventilation (MVHR) and a new electrical distribution strategy across all five floors. Party wall agreements were served and concluded with both neighbours.
Construction & Structure
The build commenced with a full strip-out followed by basement underpinning using a mass concrete method suitable for the clay subsoil. The rear extension foundations and steelwork followed, with the loft dormer construction running in parallel once the roof scaffolding was erected. Weekly site meetings and progress photography ensured quality control across all five working levels.
Fit-Out & Finishing
M&E second fix brought the underfloor heating, MVHR system and smart home wiring to life. Bespoke joinery was installed throughout, including a full-height library wall in the first-floor drawing room and a handmade kitchen with integrated appliances. Victorian plaster cornicing was restored on the principal floors while new rooms received complementary contemporary mouldings.
Handover & Aftercare
A comprehensive snagging programme was conducted floor by floor, followed by a professional deep clean and final client walkthrough. Building control sign-off was obtained for all elements, and the family received a full handover pack including warranties, maintenance schedules and operation manuals for all installed systems. Our 12-month aftercare programme provides ongoing support.
What We Delivered
Full Five-Storey Strip-Back
Complete interior reconfiguration across all five levels, removing decades of piecemeal alterations to create a coherent spatial flow from basement to loft.
Basement Conversion
Conversion to habitable family and utility space with full underpinning, tanking membrane system and natural light wells. Includes home cinema, utility room and guest bedroom.
Rear Extension & Loft
Garden-level rear extension and sympathetic loft conversion with dormers, both integrated seamlessly with the original Victorian architecture and conservation area requirements.
Complete M&E Renewal
Full electrical rewire, new heating with underfloor systems, complete plumbing renewal, MVHR ventilation and bespoke joinery package throughout all five floors.
Investment Breakdown
How the project budget was allocated across the major work packages.
Problems We Solved
Heritage vs. Modern Living
Balancing conservation area requirements with a modern family's need for open-plan living, technology integration and energy efficiency.
Heritage-sensitive detailing at the front with contemporary interventions at the rear. Reclaimed materials and period mouldings unified old and new spaces.
Five-Floor Sequencing
Coordinating complex structure-to-finish sequencing across five floors with basement, extension and loft works running simultaneously.
Phased bottom-up construction strategy with dedicated site management for each zone and weekly progress reviews across all levels.
Neighbour Impact
Managing noise, vibration and access constraints in a terraced residential setting with party walls on both sides.
Phased noisy works schedule agreed with neighbours in advance. Party wall surveyor on retainer for ongoing monitoring throughout structural phase.
Design Cohesion
Delivering a cohesive design language from a Victorian basement to a contemporary loft across five very different floor plates.
Unified material palette and consistent detailing language throughout, with period-appropriate treatments on principal floors transitioning to modern finishes above.
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Planning a Similar Project?
Whether you are considering a whole-house renovation, basement conversion or loft extension in Belsize Park, Hampstead or North West London, our team can help.