Extension to home in Norwich conservation area pays homage to traditional corbelling

Could you give us a quick summary of the project?

We’re a craft-led architecture practice, and Cast Corbel House – a ground-floor renovation and kitchen extension – is our debut project. The original building is a detached Victorian house situated in a conservation area in Norwich’s Golden Triangle and boasts original detailing that we were keen to celebrate. As a result, the extension’s facade incorporates 82 precast concrete panels, fabricated in-house, including a fascia that pays homage to traditional dogtooth-brick corbelling. In addition, the columnal pattern of red bricks was inspired by the ribbed brickwork on the existing chimney.  

What were the clients after?

They are a professional couple with grown-up children and several grandchildren. They were keen to reinvigorate their five-bedroom Victorian house to improve their day-to-day living, as well as host family and friends. We were commissioned to replace an existing extension, which was draughty and low quality. In contrast, the clients were keen to achieve longevity with any changes, so they preferred long-lasting, robust materials requiring little maintenance. They also wanted to achieve a better work-life balance in the ground-floor plan, which resulted in a new layout with distinct zones containing office, rest and social areas.

Did any external factors influence the design?

The house’s prominent corner location in a conservation area necessitated a considered approach to materiality and form. It was vital that any interventions contributed positively to the neighbourhood, which is largely made up of high-quality red-brick houses with crafted brick corbelling along with ornate cornices and chimneys. It was a challenge to do something that felt in keeping with the area while not being overly constrained. As a new practice, we had very high ambitions for the project – for what we wanted to achieve as both architect and contractor.

Tell us more about the external treatment

The extension uses traditional cavity-wall construction. The facing brickwork is arranged in a rhythm of regular projecting bays, giving depth to the facade. The brickwork is raised above the ground by matching precast footings, while a fascia of more ornate cast panels rests atop the piers. Carefully controlled ratios of iron oxide pigment were employed to ensure both panels and footings complemented the existing brickwork. The external colour palette was restricted to a red hue. We wanted to focus attention on the play of light across the facade’s relief, rather than on any one feature. 

What about the design of the interiors?

We chose rich, natural tones for the kitchen, with pops of colour introduced through seating and lighting rather than the fitted kitchen. This was a conscious decision, avoiding the need to continually update cabinetry and work surfaces as trends change. A lighter, softer palette was chosen in the dining area to create relaxing seating and emphasise the connection with the garden. The birch lining of the dining area’s ceiling draws the eye upwards and out, increasing the sense of separation from the kitchen. Interventions to the original house’s ground-floor rooms were subtle, with a focus on restoring and celebrating heritage features.

How did you tackle sustainability?

We sought to rectify pre-existing issues throughout the building. In the previous extension, draughty windows and poorly insulated walls had led to increased energy use. This was resolved by employing triple-glazing and insulation in the new extension. Elsewhere, we adopted a retrofit-first approach. The downstairs rooms were thermally inefficient, forcing the client to run the heating excessively to maintain comfort. We resolved this by installing insulation between floor joists throughout and treating the existing walls with a specialist lime render that is both insulating and breathable.

What was the most significant challenge you faced?

Honouring the ornate details of the existing house was central to the design brief – and also necessary for the planning context – but a specialist fabricator was not possible within the budget. Fabricating the panels in-house made the design possible and gave us more control over the detail. We used digital fabrication to cut inverted moulds, consisting of both plywood and rigid foam, into which we poured a rich, red-pigmented concrete. We designed and engineered our own motorised vibrating table to remove lingering air bubbles, resulting in smooth precast fascia panels.

What is your favourite detail?

It must be the precast concrete fascia. We really enjoyed the process of research, experimentation and casting the fascia. It’s a standout feature, and one we’re proud of. We’re excited by the potential of using similar digital fabrication techniques to bring craft into future projects of all scales.

Are there any particular lessons you’ve taken away from the experience?

As the main contractor, we could maintain quality throughout the build by working collaboratively with trades on site. When this approach is possible, it fosters greater understanding and respect between designer and trades. We’ve certainly benefited from their experience, and that has developed our thinking in many areas. In addition, bringing elements of fabrication in-house allowed the project to punch above its weight in terms of ambition, while helping us pick up new skills that both extend and complement our offer as a practice. Site work involved some humbling moments along the way, but also some of the most valuable lessons we learned.

Nicole Fassihi is the co-founder of Grafted

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Key data:

Total contract cost £500,000 
Area 22m²
GIFA cost per m² £3,500