Exposed blockwork walls introduce "earthy tone" to THISS Studio's Butterfield extension

The walls of this extension to a post-war terraced house in north London were made from interlocking clay blocks that local firm THISS Studio left exposed to create a warm and textural finish.

THISS Studio was asked to design a rear extension for the house, located near Butterfield Green in Stoke Newington, and to reconfigure the ground floor to improve its connection with the garden.

The clients' request for a sustainable solution led the architects to explore alternatives to conventional construction methods.

Project architect Dan Hope's research prompted the decision to use Porotherm blocks as the main building material.

The extruded clay blocks feature interlocking profiles that create structural walls when stacked. They are more typically used in large-scale commercial developments as a direct replacement for concrete blocks.

In the Butterfield project, the exposed blocks complement the brickwork of the 1970s building and introduce an attractive textural element to the new dining area.

"The Porotherm blocks, made from natural clay, have a warm, earthy tone that we wanted to celebrate within the interior," THISS Studio cofounder Sash Scott told Dezeen.

"Their inherent texture and material honesty became a key influence on the space's visual character."

The multi-cellular blocks provide several environmental benefits that help fulfil the project's brief, including excellent thermal performance that removes the need for additional insulation.

The clay material has a low level of embodied carbon and is recyclable at the end of its life. The construction method also does not require vertical mortar, which helped to reduce the project's overall material usage.

The extension's simple, robust form echoes the character of the postwar terrace, with bespoke tiles cut from the Porotherm blocks adding a decorative detail to the otherwise minimal garden-facing elevation.

"We aimed to complement the architectural language of the estate while maintaining an economy of materials and construction methods, allowing us to achieve a high-quality finish that reflects a sustainable, materially conscious approach to building," said Scott.

The internal material palette was chosen to complement the clay blocks, with affordable, readily available materials used for the flooring, joinery and exposed structural elements.

A deep red marmoleum floor provides a warm background for the space, which is unified by the consistent use of natural pine finishes across the internal window frames, joinery and custom-built roof trusses.

The extension features plenty of glazing that allows natural light to penetrate deep into the plan, while also creating a sense of connection between the living spaces and the garden.

"Butterfield is a valuable case study for us in exploring how to build smarter and more sustainably by adapting materials and technologies typically used in other building typologies," Scott added.

"The extension not only provided much-needed space but also resulted in a home that feels warm and materially sensitive – complementing the existing structure while supporting a healthy, engaged way of living with the materials that shape it."

THISS Studio is a team of architects led by Scott and his fellow co-founder, Tamsin Hanke. The practice aims to challenge conventions of buildings, objects and landscapes throughout work that combines curiosity with technical capability.

The studio's previous projects include an office interior designed using reclaimed materials and another extension with a curved aluminium roof that resembles a fried egg.

The photography is by Henry Woide.

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