Building from the ground up

There has been a huge resurgence of interest in building with traditional materials such as rammed earth and structural stone. These materials are becoming common place in small, bespoke design projects but are often missing in large commercial work where concrete remains king. Nikolay Shahpazov is a man on a mission to change our preconceptions that sustainable materials are challenging to use at scale.

Having joined Bennetts Associates in 2019 to work within their dedicated sustainability group, Shahpazov was keen to apply his interest and knowledge in sustainable materials in practice. The opportunity came with The Apex, one of the five building that form Tribeca, a large-scale life sciences development in London’s Kings Cross for developer REEF Group. The mixed-use scheme replaces a former Royal Mail sorting office, with the first phase including The Apex completing in Autumn 2024.

Shahpazov saw an opportunity to reduce the embodied carbon of the project by using innovate earth blocks, a decision that involved working closely with Buckinghamshire-based brick makers HG Matthews and earth expert Roland Keeble of Rammed Earth Consulting. Shahpazov was aware of family-owned HG Matthews research into the carbon reduction of brick manufacturing. The business was already producing an earth block as a natural, low-carbon alternative to fired bricks and had switched to biomass for the drying process to further reduce carbon.

Unfired earth blocks can be made into new blocks free of waste. Any broken or damaged blocks can be reshaped and reprocessed. Photo by Will Claxton.

Supported by an enlightened client, the REEF Group, who are committed to recycling or reusing 95% of the waste from existing buildings on site, Shahpazov’s journey began by sending a sample of the site’s London clay subsoil to HG Matthews for analysis. Shahpazov then set to work at HG Matthews alongside Keeble to refine the subsoil, mixing it with local straw and clay to perfect the recipe. It was a process of experimentation and testing and of the three different block mixes made, the optimum mix proved to be half subsoil and half sand and straw.

The making process moves the earth mix through a feed hopper and a final set of rollers to crush any larger pieces of earth before it reaches the blockmaking machine where wooden block moulds follow a circuit. Biomass boilers using locally sourced renewable timber dry the blocks at 50°C. The production process uses rainwater harvested from the HG Matthews site to fit within environmentally respectful intentions.

The next challenges mirror those faced by other sustainable materials; a lack of warranties on structural and fire performance and the necessity for both client and contractor to buy into an untested approach. With the REEF Group on board, the commitment of contractor VolkerFitzpatrick and blockwork subcontractor Turick was pivotal to the success of the project.

The earth blocks are removed from the timber moulds before being placed on metal trays for drying. The unfired blocks are dried for up to 7 days using woodchip boilers at a temperature up to 50C. Photos by Will Claxton.

With a strength of around 6.5N/mm2 - equivalent to medium-density concrete blocks - laboratory tests showed that the block samples produced would work in the basement in place of concrete bricks. Timing issues over fire integrity relating to dividing walls between rooms necessitated the team specifying the blocks for the perimeter walls rather than throughout the basement as originally planned. The blocks passed the test for fire spread, vital in demonstrating they would not contribute to fire spreading. Post completion, fire separation tests proved the blocks can be used between rooms providing a fire rating of up to two hours.

Shahpazov believes the blocks would have fulfilled the original brief if they’d had more time to gather data. The blocks are structural but were used in a non-loadbearing capacity, lining the inner face of the concrete retaining walls and installed on their side, rather than on edge, which used more blocks. The lack of warranty necessitated the gathering of all evidence and email correspondence into a large document. Although currently the same cost as traditional concrete blocks, more of the earth blocks are needed per square metre but with increased demand, the price will fall. Shahpazov also notes that switching to earth blocks saves money by avoiding landfill in relation to site excavation, and the tax associated with this. Notably, convinced by their use, the developer is continuing to specify the earth blocks for the remaining buildings in the development.

The blocks embodied carbon is only 1/10th when compared to medium density blockwork. Photo by Will Claxton.

HG Matthews are actively engaging with architects and engineers on the potential use of their ‘Strocks’ to significantly lower the embodied carbon of future projects. There are other benefits too; from lack of toxic substances, to regulating indoor temperature and humidity levels, to trapping airborne pollutants. These bricks made with clay rich earth and straw sourced from within a mile of the brickworks and dried using their biomass boilers should prove a valuable addition to the palette of sustainable materials available to architects like Shahpazov who are seeking alternatives to the carbon intensive status quo and looking to build from the ground up.

Vanessa Norwood is a curator and consultant for the built environment advocating for low-carbon architecture and materials.