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Why Passivhaus Makes Sense

Gale and Snowden is an architectural practice based in the South West. The RIBA award winning practice exclusively focuses on delivering ecological designs, with an emphasis on buildings that use as little energy as possible. Their recent designs for public sector housing epitomise this approach and demonstrate why Passivhaus is the most effective build method.

A pilot project for Exeter City Council involved the development of infill land, and building two residential blocks of 21 units to meet the Passivhaus standard.

The build method uses solid wall construction, incorporating 215mm of dense concrete blockwork faced with a StoTherm Classic K system, resulting in an external wall U-value of 0.1W/m²K.

The client requested that the buildings should meet the performance criteria of Level 4 of the Code for Sustainable Homes. A workshop was set up involving the Council and various stakeholders, including construction professionals, to agree on the most effective (and cost-efficient) way of meeting this performance.

The lead architect on the project is Tomas Gartner. He is a certified Passivhaus designer and an assessor for the Code for Sustainable Homes, so was able to make highly informed recommendations.

"The Code for Sustainable Homes cannot be directly compared with Passivhaus. Passivhaus is an energy performance standard while the Code takes a more holistic approach that also includes, for example, waste, water and construction management. In terms of evaluating the performance of the individual building, the Code uses the SAP method to predict the future energy requirements of the building.

"We found that Passivhaus is simply a more reliable way of estimating energy requirements than SAP. We worked out requirements using both Passivhaus and SAP methodology and our findings indicate that the energy use predicted by SAP can show a far lower heating demand than the houses demonstrate in use.

"Passivhaus is also more suitable as a design tool to support the architect to optimise the performance at the earliest design stage. The Passivhaus planning package allows a designer to check their design early in the project and then to refine it as plans progress. Whereas SAP is far less easy to amend, so it doesn't help me as a designer to fine tune the designs.

"Our designs focus on a fabric first approach, whereas the Code allows for micro-generation technology to be included in the calculations to offset CO2 emissions to demonstrate compliance with Code 4. Our view is that it is far more logical to first build the energy efficiency into the fabric of the structure and only use micro-generation to meet the higher Code 5 or 6 levels.

"It is our experience that Passivhaus has beome more widely accepted in the UK and there is greater familiarity with the concept. We think this process will accelerate as the ease of using Passivhaus is better understood and as live projects demonstrate the great range of high quality designs that can be produced."

The project for Exeter Council is part of a Technology Strategy Board monitoring project, and the performance of the buildings in use will be the subject of ongoing observation. There are a total of 20 sites under consideration and twelve currently have planning permission. The first two residential blocks are now complete and work is starting on a further two sites.