Problem addressed

Unfired clay in production has very low emissions due to being dried instead of fired. In use clay can be structural but in sustainability terms its mass means it can be used to buffer heat in both hot and cold weather, resulting in energy savings. It also manages internal humidity meaning air quality, health and wellbeing are improved without mechanical electrical costs throughout the buildings lifetime. Clay also sequesters VOCs, particularly formaldehyde, a major indoor pollutant.

Solution overview

Strocks are moulded clay blocks made from clay and straw. They are made either with HG Matthew’s own clay or with clay extracted at site and transported to them and then back to site. The clay is dried but not fired, a massive energy/emissions saving.

Clay blocks can be used like bricks in most ways except as an outer leaf. They are load bearing, fire proof and sound attenuating. For users looking to reduce waste from site they are a good way to turn excavated material into useful products on site. They can be used with most other building systems, tied to other structures, loaded with floors and roofs, fixed with insulation materials and services. They can be plastered, ideally with clay plasters which are also vapour permeable, low emission and re-usable.

They can be used in public or residential settings where they perform the dual functions of improving air quality through humidity control which is innate to unfired clay and they sequester VOCs.

Maintenance over time may include re-finishing with sodium silicate, linseed oil or similar, or re-plastering or painting with clay paint as with all or any brick or block wall.

Cost Benefit

Costs vary depending on the scale of the contract but blocks typically start at £1.80 per block and rise from there depending on the clay used, difficulty of processing and transport.

Walls are typically a fairly low cost in building contracts, percentages vary, but on a typical recent project the savings in land fill tax were three times the cost of the blocks produced from site ‘waste’.

Clay blocks are fully recyclable/reusable and have no end of life.

Case study

Developers GS8 produced The Arbour in 2022. It is a mixed housing development which used the spoil produced from the foundations to make Strocks for use in the party walls. Although the structure is a high performance Passivhaus design with structural timber throughout the blocks serve a number of functions in the building. From the developers perspective the savings in landfill tax was a major reason to use the process and a cost saving. The buildings have sound and fire attenuation through the use of the blocks and in an unfinished condition they provide a character and aesthetic which have added to the value of the finished products.

The unfinished blocks also improve the indoor air quality, very important for tightly sealed homes with HVAC systems and sequester VOCs, equally impactful in draft free homes.