Passivhaus diaries, part three: Dr Wolfgang Feist, the Passivhaus guru

I am just back from an inspiring AECB conference. The AECB (Association for Environment Conscious Building - www.aecb.net), also known as the sustainable building association, is a membership association for all those engaged in sustainable building and incorporates everybody from architects and builders to enthusiastic self-builders.

Chris Herring, Steve Slator and I, the three Green Building Store directors, have been members of the AECB since its launch in 1989 and Chris is currently its national chair.

Tackling climate change is a top priority for the AECB and its CarbonLite programme promotes the Passivhaus approach to low energy building.

This year the AECB was honoured to have as its keynote speaker Professor Wolfgang Feist, founder of the Passivhaus Institut in Germany. Wolfgang, along with Swedish Professor Bo Adamson, pioneered and developed the Passivhaus design methodology basing their ideas on the robust application of building physics.

On the first night of the conference a group of us had a meal with Wolfgang and he expressed his interest in our efforts to build a Passivhaus in the British vernacular style using cavity wall construction and was very reassuring about its achievability. His keynote lecture was also encouraging and reassuring about the robustness of the Passivhaus methodology in general - and also answered the age-old question about the opening of windows in Passivhaus buildings.

People are always concerned about what happens when you open windows in a Passivhaus - Wolfgang was able to reassure us that it would have little impact on the ventilation system - as it would have a similar effect to opening windows in a standard house.

The conference was also a great opportunity to meet architects and specifiers interested in Passivhaus design. Our Denby Dale Passivhaus, the subject of these Passivhaus diaries, was flagged up in one of the lectures at the conference as one of five exemplar Passivhaus buildings currently underway in the UK.

The CarbonLite Programme promotes the uptake of Passivhaus design through continuing training courses on using the Passive House Design Package, The AECB has just completed its guidelines for a “gold standard”(like Passivhaus but with extra emphasis on energy efficiency of appliances lighting etc). We all came away feeling excited and encouraged about moving Passivhaus forward in the UK

On site

Excavation has gone very well and, thankfully, to budget and with no surprises. We've stripped the site, leveled it and a local farmer has taken the spoil to make use of it. We've excavated the trenches and have added the concrete, which is the same as any strip foundation apart from being wider because of the thickness of the walls - 225mm thick and 850mm wide. Kirklees Building Control have visited and approved depth of foundations.

This week we will be getting on with the footings and starting work on the blockwork substructure. After we've built the blockwork around, we will then put in hardcore (crushed stone) in 150mm compacted layers as normal. On top of the hardcore we'll be putting in sand blinding, insulation (225mm of Knauf polyfoam), damp proof membrane, followed by reinforced steel mesh and spacer blocks.

After that, we'll pour in the concrete (100mm) with a power-floated finish - ready to receive tiling or engineered timber flooring. There is nothing unusual about this - it is the simplest sort of floor you can have. The only Passivhaus detailing to this part of the build comes with the way we detail the concrete slab at the edge and the inner leaf blockwork specification.

The slab will be poured across the top of the blockwork inner leaf to minimize the subsequent shrinkage cracking between the wall and floor elements, an area that we identified as a major airtightness problem on the Longwood House we built in the early nineties. The blockwork below the slab will be built of lightweight insulated blocks such as 7N/mm² Celcon to help to minimize the only major thermal bridge in the build.

Hopefully the two sectional images of foundations below will help illustrate this. They show a typical section through the foundations. The second one demonstrates the added complication of an external door threshold.