Make your home as energy efficient as possible with a Passivhaus grade whole home retrofit. Here's what you need to know about EnerPHit.  

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Image: Arboreal Architects

EnerPHit is the Passivhaus certificate for retrofits. Retrofitting your home is an expensive process but one that will ensure your home is performing at its best and most efficient. The Passivhaus Institute has introduced a step-by-step certification approach, which allows projects to be undertaken in two or more parts with the help of an EnerPHit retrofit plan.

The Grand Designs magazine team spoke to Tom Raymont from Arboreal Architecture all about carrying out the EnerPHit process for ensuring a warm home.

Experience is key

Start with a good architect, one with experience of a deep retrofit and preferably an accredited Passivhaus designer who has expertise in understanding how heat, air and moisture move through a building. An independent assessor, working alongside the Passivhaus-trained architect, is required if you want to achieve a certified Enerphit retrofit, though you don’t have to certify your project, and there are additional costs involved.

Read more: Sustainable retrofit: what you need to know

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Image: Arco2

Design changes

Adding new layers of insulation to the inside or outside of a building can change the building’s appearance and the details at windows, doors and other junctions. Technically, moisture is the key issue and it’s very important that the condensation risk is designed out. Traditional insulation products are often the most reliable. Wood-fibre boards, cork boards and blown cellulose all have excellent performance, are plant-based and are breathable.

Read more: A guide to insulation for walls and floors


It’s possible to achieve airtightness in an older home but it is a technical challenge. Most buildings are quite leaky, even if you can’t feel a draught. A deep retrofit to Enerphit standard can involve improving airtightness by a factor of ten. A mechanical ventilation with heat recovery system (MVHR) is often quite an expensive part of the project but they are not difficult to install. Consider MVHR once you are sure the fabric of the building is as good as it can be.

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Image: Johnson Naylor 


Electric heating for spaces and hot water is the future direction. Air source heat pumps offer the best mix of performance and cost, but for a bit more money a ground-source system will lower energy use further. If you sign up for a 100 per cent renewable electricity tariff you can live in a zero-carbon home.


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