Passivhaus retrofit – making Devon homes sustainable, beautiful and comfortable

In June 2010 Building Devon took on our first Passivhaus retrofit (passive house) project near Dartmoor.

By using the simple ‘tea cosy’ effect of super-efficient insulation and excellent airtightness coupled with a ‘comfort ventilation’ system, Passivhaus design can create healthy and comfortable homes that require minimal heating. Heat generated from the sun through windows, occupants’ body heat and cooking and showering activities are often all that are needed to warm a Passivhaus home. Passivhaus dwellings typically achieve an energy saving of 90% compared to the average existing house and 75% saving in space heating compared with a new house built to our current Building Regulations.

What we did

The first part of the project was quite typical of a normal renovation: rip out, move layouts, repair defects etc. It was when we started the first fix stage that we started to step away from the normal routines.

We started with the existing foundations and drainage. This was all done to the air tight and thermal regulations of a Passivhaus.

Externally, on the non-granite walls, 250mm of EPS (polystyrene) was used to insulate the building. The new triple glazed insulated windows fitted to a 75x75mm sub frame were bolted to the walls.

Internally, on the granite walls, 100×50 stud walls were constructed with a 20mm cavity. The walls were backed with a breathable membrane (to stop contact), insulated with 100mm mineral wool and then the Intelo membrane was stapled on and counter battened. The counter batten acts as a service void. Finally, 50mm of closed cell insulation was put between the counter battens before plaster board.

One crucial element of a retrofit is to ensure the connection between various components of the structure are air tight. Here this is achieved using various tapes from the Intello range, OSB, Ply, DPM, existing & new render.

The ground floor of the existing building (suspended timber floor) was removed and refitted with hardcore, concrete, 250mm EPS and screed. The DPM was used as water, air and radon barrier and linked to the walls. The attic had a layer of OSB laid over the top of the joists, which was taped and linked through to the walls below. 500mm of EPS was then fitted over.


Upon completion our clients are very pleased with the end results, and their reduced energy usage. Working on a project like this has made us aware that current Building Regulations and building practice are lagging behind what is technically possible. We have gained an enormous amount of knowledge on how to improve the performance of the buildings we work on. We often surpass Building Regulations and are able to put that ‘passivhaus’ knowledge into action on all our projects, reducing the carbon footprint of buildings for the future, reducing energy bills and  helping the future of our planet by making building sustainable.

Westcott House was designed by Gale & Snowden Architects, who also designed two previous Passivhaus projects we worked on: Westcott House (Passivhaus retrofit) & Bampton (Passivhaus new build)

More of Our Previous Projects