Basket-weave stone brickwork animates the facade of Hackney house extension

Can you briefly describe the project?

The project is a single-storey rear and side extension to a mid-terrace Victorian house in a Hackney conservation area, east London.

Who is the project for and what was the brief?

I was approached by a family coming to a crossroads. They had owned their house for a few years, were very embedded in the community and their children were about to finish secondary school. Their initial brief mentioned a home for the next 20 years, which captivated me.

Were there any significant factors that influenced the design?

The existing Victorian building had a double-storey rear outrigger with a flank wall that was bowing, but not structurally an issue. The neighbours had demolished their own outrigger flank wall and rebuilt anew to achieve a flat surface for their fully glazed side extension rooflight to intersect cleanly.

Although my clients were keen for a largely glazed side return, they were not prepared to undertake such extensive demolition. We worked together to generate a design using an off-the-shelf rooflight that aligned with the interior and minimised the rooflight frame and edge inside. This enabled the budget to be spread elsewhere – namely the bricks.

The clients did not want their extension to cast shade (literally and figuratively) on the neighbours, nor did they want to lose too much garden space. Therefore, the project was designed to sit between and follow an S shape as it gently mediated between the adjacent extensions.

What was the external treatment of the project?

The rear extension brickwork comes from the desire to break down the massing and not intrude significantly on the garden. The clients used their garden frequently for relaxing, entertaining and gardening, and enjoyed its courtyard-like quality, shielded by a gable wall of the adjacent street terrace.

The basket weave pattern achieves this by being partially open, revealing a searing yellow layer as you get closer. At certain times of day, the intense south sunlight hits this yellow, animating the facade with shadows. Its contemporary design aims to be a playful, wry nod to follies or grottoes found in English Romantic gardens. In short, the extension is just as much an extension of the rear garden as it is of the main house.

How did you design the interiors?

The clients favoured a ‘galley-plus’ kitchen arrangement with preparation space sitting 1.5m aside full-height openable pivot doors. The doors have flush reveals, detailed to ensure that, when open, they reduce the interference of the frame with the view beyond.

The plan now enables flexibility of the dining table position – a simple 90-degree turn transforms everyday use to entertaining 10-plus guests while the front reception rooms directly connect to the kitchen.

What was the project’s approach to sustainability?

A building that was not performing well for family life has been extended and made more thermally and acoustically comfortable for years to come.

In the process, we acknowledge we used high-carbon content materials: metal, glass, ceramics, polymers and concrete are all there. Could the extension have been leaner? Yes and no. But behind all the decisions of each material used is a new addition that now better maintains a comfortable internal temperature, despite the south sun, due to triple glazing and other fabric-first principles.

The building envelope is a double-skinned block with PIR insulation both in the cavity and internally with insulated plasterboard – using readily available trades to ensure the outcomes were predictable and could perform as planned. The thicknesses of the insulation goes beyond building regulations and uses a base bedding course of insulating ‘bricks’ by Marmox to the inner leaf of block to provide floor and wall insulation continuity. The stone bricks offer a significant carbon saving over their kiln-formed cousins and, twinned with lime mortar, are recyclable.

What was the project’s main challenge and how did you overcome it?

The stone bricks are a product that’s relatively new to the UK market. It is our understanding that this is the first domestic project where Polycor’s Messangis Limestone has been used in the UK. Since they are termed as ‘bricks’, they follow European classification, meaning they follow certain dimensional tolerances: one in ten of the brick batch needs to meet the dimensional tolerances. Just one in ten for a product that is cut – not clamped and baked!

Some of the bricks were more than 5mm out from the expected size due to a change in Polycor’s stone cutters over an August quarry shut-down. So we had an issue with certain brick lengths and widths supplied in the consignment not meeting the expected dimensional consistency. This issue was quickly resolved by EH Smith and Polycor with further stone bricks provided without charge or delays incurred.

What was your favourite moment in the project?

It was a privilege to be invited to dinner by my clients at their house. Beyond their really good cooking, it was pleasurable to watch how they work together, creating a meal in an efficient and practical kitchen space that is bespoke to them and their needs. You do get a glimpse that all that detailing and decision-making was worth it and hopefully will be so for years to come.

Are there lessons from this project which might be applied elsewhere?

This project has been a welcome opportunity to use stone that continues Draper Studio’s design enquiries into using more natural and self-finished materials. It’s been effective because the stone comes in a familiar format that makes its adoption on site as seamless as possible, but as ever there were teething issues.

Polycor’s Messangis quarry repurposes smaller blocks of stone unusable for large slab orders. These odd blocks are then sawn into standard metric brick sizes, which in time can (and will) have more dimensional uniformity than the initial batch we received for this project.

Looking beyond this project, it’s evident that established bricklaying trades are well-placed to substitute conventional clay-fired bricks for stone versions. Stone bricks have a lower embodied carbon footprint and, in my view, have a more premium appearance over clay-fired bricks.

It has prompted the studio to relearn what we do with stone. Our aim is to take the material, deployed here as unashamedly decorative, into more structural applications. For this to be successful, the whole consultant, supply and construction chain needs a rethink on weaning itself off concrete and steel where possible.

Adam Draper is founder of Draper Studio

Read more about Hackney House’s upcycled limestone bricks

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Key data:

Total rear extension cost £200,000
Area of extension 37m²
GIFA cost £5,400m²