Some of the most exciting images we’ve seen during the global shut down, is how quickly planet earth seems to re-balance itself when mankind is interrupted in its daily grind. Keeping half the world’s population under lock down is obviously not sustainable but we can and should improve the way we build to minimise our impact on the environment.

**Hook Norton Low Carbon Development by Charlie Luxton Design**

We have recently had the pleasure of being involved in the low carbon calculations for the Hook Norton Low Carbon Community Housing project which compromises of 12 dwellings units, a community building and a new shared outdoor space designed by Charlie Luxton Design. The project has recently been submitted for planning.

The homes combine design and environmental merit and will be built to Passivhaus standard. By achieving a high level of air-tightness, maximum comfort with low running costs and reduced carbon emissions will be ensured. The houses are positioned on the site to make the most of renewable energy features like solar photo-voltaic panels with an extensive array on each roof and on the community building.

The challenge

This project has set itself the ambitious target of achieving carbon neutrality both during construction and occupation. Translating this and the other sustainability concepts identified and supported by the community into a reality is best achieved by considering the built form and its systems as an ecosystem with flows and interdependence.

**Carbon neutrality and sustainability diagram by Charlie Luxton Design**

Our approach

SOLID has used The Life Cycle Analysis (LCA) tool to model the potential for carbon neutrality of the structural and civil engineering elements. We base our calculation on the LCA standards (CEN/TC350, ISO 21930). The design has followed the RICS building stages.

One of our principles is to reduce embodied carbon by using more recycled materials and materials that are produced using less fossil fuel. However, in order to achieve carbon neutrally, it is necessary to provide solid engineering structures that can restore climate. This is achieved by creating structures that are material banks which can be re-used in the future and are sequestrating carbon. This approach reduces substantially the strain that is put in the environment.

Benchmarking

Our calculations also looked at the embodied carbon performance of the structure in relation to residential developments in Europe, using the ‘Cradle to grave’ methodology. The analysis below is based on residential construction in Timber Frame and trench fill foundations. At this stage, this development is in category B, which is showing high performance. However, our aim is to get to level A by improving the selection of materials.

The detail

In order to identify the material constituents of the structures that should be targeted, the carbon model gives us more detail on their distribution within the fabric of the building.

In this project, the interaction between the ground bearing slab and foundation is important as it will have a direct carbon reduction on the sub-structure (horizontal structures in graphic)

Our approach is to use light weight structures and we proposed a raft foundation that distributes the building load. This option uses less cement first and foremost, while reducing aggregates and water content.

Another item to target is the reduction of other structures and materials. This relates to external works, ground infilling and underground pipework. This element is clearly identified in the Sankey diagram Graphic. Our approach is to replace U-PVC plastic and virgin bedding material for Clay Pipework with recycled bedding and concrete chambers.

**Sankey diagram comparison between project stage, construction items and material use**

If we drill down even more, we can see which material produced the greatest impact. This allows us to specifically target material types and specific manufactures. In this case, we can concentrate on concrete and the external envelope of the building. See Graphic 6 for details.

We are also looking at replacing high embodied energy materials such as Portland Cement in concrete with alternatives including fly ash and ground granulated blast furnace slag (GGBS) and its availability within the Oxfordshire supply chain

On the super structure, we are assessing the use of natural raw materials which includes timber, cork and bamboo. Natural insulation materials including wool and alternatives to plasterboard lining are also been assessed to determine which can be available within the Cotswolds or are produced in the near-by areas.

A low carbon future

SOLID.