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Building study: Finkernagel Ross perfects the minor details

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Finkernagel Ross’s razor-sharp contemporary addition to a listed detached property in Hampstead is strangely suited to its stout Victorian host, writes Jay Merrick


When architects design a sizeable building, its major characteristics don’t always encourage us to take in minor architectural details. How different with house extensions, where minor can’t help seeming, for better or worse, very major: the precise double-angled fall of the cement fibreboard cladding of Doma’s Lean-To in Harrogate, for example; or the joints in the pleated ceiling of Bureau de Change’s Fold extension in Haringey; or Archmonger’s kit of estranged parts poking out of the skinny brick and tile rump of the Clock House in Finsbury Park.

There is a great deal to absorb in these projects, perhaps even a sense of architectural ‘overexistence’, as if performance artists were upstaging their hosts. In Wedderburn Road, off Haverstock Hill in Belsize Park, London, the hosts are more or less grandly domestic Victorian buildings, many with imperiously lavish modulations of form and detail. 

The Grade II-listed 3 Wedderburn Road was designed by Horace Field in 1886, and it ticks the Vernacular Revivalist boxes: asymmetrical form, hipped roof, leaded casements, stone mullions, recessed gabled wing with arcading, Tudor-style entrance, decorative stone, Arts and Crafts garden walls. Projecting from the brickwork on the east side of the rear, south-facing façade is an extension, designed by Finkernagel Ross, whose architecture could not be more distinctly different. It is, essentially, a steel ring beam concealed in a thin-sectioned, substantially glazed flat roof, whose shallowly angled, porcelain-clad 600mm soffits cut back like floating cornices to meet two entirely glazed, outward-facing facades. 

The ring beam follows the rectangular plan of the extension’s frameless skylight and is anchored to a concrete padstone in the brickwork of the home’s garden-facing elevation, and to two concealed columns behind kitchen cabinets along the east side of the extension. A single very slim polished steel column just inside the glazed elevation on the opposite of the extension is the only other prop for the ring beam. 

The canopy is so finely tailored in its details, and so minimally supported visibly, that the eye looks for more. Phenomenologically – or just for fun – the extension could be seen as a Modernist wing-collar sticking out at right angles from a stoutly rubicund Victorian neck.  

The design process involved an obsessive search for technical solutions, with full-scale assemblies of the most challenging feature

Three things make the architecture work. Firstly, the refinement of the extension’s structure and details, which are super-crisp, but not fatally super-demonstrative; secondly the tableau of the extension and the new garden terrace as a whole; thirdly, two small articulations in plan concerning the rear elevation of the house and the way the extension joins it. 

The design process involved an obsessive search for detailed technical solutions, with full-scale assemblies of the most challenging structural and architectural feature – the coming-together of the box-sectioned ring beam, soffit, and cladding. The initial design concept for the extension was expressed in a roughish foam model. The challenge of designing the unsupported right-angle of the structure, where totally glazed walls come together along two sides of the extension, began with architectural sketches of the ring beam’s relationship with the soffit. The engineer supplied a 3D model, and this led to glazing shop drawings, then detailed drawings by the architects; and, finally, an accurately built 1:1 model of the structure, soffit, and glazing junction (pictured below).



The soffit is clad in precisely cut 6mm-thick Calacatta marble-effect porcelain facings. These 29in-long sheets had to be handled and aligned with great care as they were applied to the multiboard on the soffit’s substructure, whose cantilevered and cranked steel pieces were bolted to the ringbeam. 

The lines of the glazing header channel and the edges of the facings had to be perfectly straight and parallel, and seamlessly butted at the corner. This signalled the clarity and precision of the extension’s design and making. The linear lighting track, parallel with the glazing, and narrow slit of the drainage channels outside the bottom tracks of the glazing are like cut-lines in car bodywork.

The architectural refinement of the extension’s form and detailing is remarkable

The architectural refinement of the extension’s form and detailing is remarkable, but the way it sits on a very well designed terrace made of the same off-white microconcrete as the floor of the extension is an equally crucial outcome. The structure, terrace, and single shadow-gapped step down to the garden make an excellently restrained  composition dominated by white horizontals; the colour of the microconcrete is more or less identical to the stone mullions of the home’s rear elevation.

The design was significantly improved by two adjustments to the plan, one to the rear of the house, and one to the extension. The brick garage-cum-home gym which protrudes onto the terrace was remodelled to form a rectangular nook where it meets the side of the house; another nook, the width of the projecting soffit, was made where the side glazing of the extension meets the back wall of the house. These are small but adroit moves, adding a compositionally important sense of light-touch articulation to the extension and terrace.       

The extension is more than a demonstration of purified Modernist form and structure. There are two unexpected architectural conceits at play. The first has a 16th century date-stamp. Finkernagel suggests that the marble-clad soffits are neo-Mannerist. One hardly expects them to recall Romano’s Palazzo del Te in Mantua, but the conceit is too much, and it would be safer to imagine that the grey-veined porcelain has more to do with, say, the Alpine marble of Mies’s Barcelona Pavilion.

Wedderbrun road 6

Wedderbrun road 6

The second conceit is more interesting and satisfying. The project included the remodelling of the lounge that the extension is attached to. This tall volume was originally irregular in plan due to two masonry structural piers on one side. The architects created an internal box veneered with crown-cut American black walnut to conceal the piers and make the plan square. 

‘It’s our Soane room,’ says Finkernagel Ross co-director Catherine Ross, referring in particular to the Breakfast Room at Sir John Soane’s House. ‘It’s a direct contradiction to the architecture of the extension.’ But surely not to the historical macaroni of Horace Field’s building. Finkernagel describes the lounge – whose suspended ceiling, like Soane’s saucer dome, stops short of the walls – as a postmodern point of transition: Victoriana on one side, razor-sharp Modernism on the other.  

If one detached the extension and stood it in the garden, away from the house, its architecture would be an absurd interloper. Yet, attached to Field’s architecture, it is not an affront. The extension manages to seem both utterly counter-contextual, and utterly deferential; ‘strangely suitable’ might be another way to put it. Either way, the lack of tension between the architecture of the historic and new forms is remarkable, and this makes Finkernagel Ross’s minor addition a relatively major achievement.

Jay Merrick is the architecture critic of The Independent

Project data

Start on site June 2015
Completion April 2016
Gross internal area 29m2
Gross external area 33m2
Project value £249,000
Form of contract JCT ICD 2011 and direct trade contracts
Architect Finkernagel Ross
Project manager Finkernagel Ross
Structural engineer Structure Mode
Building inspector Act Building Control
Lighting design Atrium
Main contractor AODS Building Contractors 
CAD software used AutoCAD LT 2016
Annual CO2 emissions 68.823kg/m2 (e)

Client’s view

Our house is a detached, listed property in Hampstead, North London, which we wished to extend into the rear garden in a way that would maximise light and blur the boundary between inside and outside. It was also important to avoid obscuring the rear of the house in order to satisfy Camden Council’s planning department. Finkernagel Ross produced a very elegant design that satisfied all our requirements and successfully negotiated the approval of the planners.


Finakernagel ross drawings for web4

Finakernagel ross drawings for web4

The most important working detail was the section through the floating canopy, which had to resolve structure, rooflight, sliding screen, lighting and the cantilevered brise-soleil. The challenge lay in reconciling the delicacy and aesthetics of the design intent with structural, thermal, and other practical requirements.

The detail was developed in numerous iterations of two-dimensional and three-dimensional representations, both in sketch and CAD forms, in an ongoing dialogue with the structural engineer. Despite the simplicity of the actual element of the canopy – or perhaps because of it – it became apparent at some point that the means of standard architectural representation, all in the realm of the virtual, were too limiting to fully understand how the detail should be constructed. The development of this critical detail culminated in our building a 600mm-long section of the detail as a 1:1 prototype, using actual building materials and methods of construction. Using this prototype, we were able to test and finalise the detail design, and inform the production information and procurement of the project. 

Once all trades were appointed, the prototype then served as an illustrative and informative tool for the contractors, with whom we carried out workshops at our office before construction commenced.

Felix Finkernagel, director, Finkernagel Ross

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