Thursday, 7 November 2013

Grand Designs Zero Carbon Cob Passive House

One of our projects recently featured on Channel 4's Grand Designs.  More information can be found at the following links:

Kevin McCabe Ltd.
Build Something Beautiful

Grand Designs

Kevin McCabe Ltd master cob builder based in Devon approached our building physics and engineering department to assist with developing the thermal, energy and mechanical strategy for his new cob building project Dingle Dell.  The Dingle Dell project turned out to be grand in every sense.   Local planners had stipulated that the scheme should not only be outstanding in its design and architecture but also be environmentally sensitive and must achieve code 6 of the Code for Sustainable Homes.  Two of the key elements of the code 6 requirement was that firstly it be totally zero carbon not just in regulated emissions from heating and hot water but also from non regulated emissions including appliances and sockets - all power.  Secondly that it achieve a heat loss parameter (HLP) of 0.8 W/m², a level currently only being achieved by the Passivhaus low energy standard.  As we are experienced in dealing with natural materials in building design our role was to investigate and advise on how the HLP could be achieved with a cob building. 

Working with the project architects, Bedford and Jobson, we assessed various fabric and window U-values, thermal bridging and different air permeability and ventilation strategies before finally arriving at the most appropriate solution for the scheme to achieve the HLP.  The zero carbon requirement was quite a challenge due to the size of the property so a high mix of renewable energy technologies was required.  We investigated the mix of water and wind turbines and PV technologies and assessed them in conjunction with other technologies such as biomass, heat pumps, MVHR and solar thermal to determine what was required to achieve the zero carbon requirement.   The final result being a truly grand design cob house that is totally zero carbon and who's energy performance rivals that set by the Passivhaus Institute - the first of its kind in the world.     

Wire frame image of 3D thermal model.

Due to the high levels of insulation required and the high levels of south facing glazing for winter solar gain our physics department then carried out a 3D thermal modelling simulation exercise using IES software of the design.  Thermal modelling enabled us to determine natural ventilation strategies to limit any potential summertime overheating.  We modelled and thermally assessed the cob mass and how effective it would be at stabilising temperatures.  We simulated stack ventilation and cross flow ventilation strategies.  We also carried out a 3D daylight modelling assessment to ensure that daylight levels would be appropriate when using triple glazing or even quadruple glazing in thick cob walls. Due to the added requirement of insulation these cob walls were thicker than normal.  

In addition to these services we also provided the Code for Sustainable Homes assessment developing the code 6 strategy and provided a specialist thermal bridging assessment of the scheme.   This is a remarkable project that we were happy to have played an integral part of.  

Gale & Snowden provide mechanical engineering and building physics services to architects, designers and construction professionals.  These include:

  • Thermal and carbon modelling
  • Passivhaus design consultancy
  • Low energy mechanical engineering
  • Renewable energy engineering

Full information about these services can be found on our website here.