HPH014 : Low Energy Barn Conversions – with Bill Butcher from Green Building Store
Bill Butcher from Green Building Store shares his approach to creating a low energy barn conversion by building a box within a box. Stirley Community Farm will meet the EnerPHit standard.
Interview with Bill Butcher
Bill started out, aged 16, at the tech college in Exeter doing an HNC in building. From there he pursued the quantity surveying route, before becoming a builder. He has always had an interest in the environment and founded Green Building Store with two other colleagues in 1995. Green Building Store focusses on supplying the components and services around low energy and sustainable construction.
In 2007 They Realised The Potential of Passivhaus
Bill tells the story of how his business partner, Chris Herring, had been over to Bregenz for the Passivhaus International Conference and had come back convinced that their business should go down this route.
An Opportunity Presented Itself in Denby Dale
When Geoff and Kate Tunstall approached the Green Building Store about constructing a ‘green house', which in their eyes was going to be a dormer bungalow with a low of renewables, it presented the perfect opportunity to construct their new home to Passivhaus standard. In 2009, they started building. You can read a comprehensive blog on the whole project.
To Keep The Price Reasonable, Builders Will Stay Within Their Comfort Zones
As Green Building Store had built with masonry and cavity wall in the past, this was the approach taken at Denby Dale. This meant that all the materials were available locally in Huddersfield, with the exception of triple-glazed windows with insulated frames, mechanical ventilation heat recovery (MVHR), and various tapes and membranes (all of which are now handily stocked by the Green Building Store!).
Passivhaus is Not Restricted to a Single Construction Methodology
Bill talks about other examples including John Williamson from JPW Construction building with timber frame and Bere Architects using a kit home imported from Austria for the Camden House.
Passivhaus is as Much About Comfort as Anything
Benefits of a fabric first approach not only include the performance of the building, but you also create an environment that is tranquil and comfortable. Even when it is -10°C outside there'll be no internal surfaces less than 17°C. This drastically reduces convection. Bill explains with an analogy of standing in front of a fire on Bonfire Night, where you're burning on the front side but freezing on your back! In a Passivhaus where you don’t have that convection of cold air falling you can keep the thermostat down to 18°C, whereas in a conventional build you might have to adjust the thermostat to 23°C to counteract that feeling.
Stirley Community Farm
These were three bankrupt dairy farms on the outskirts of Huddersfield (in quite an exposed location) that were owned by Kirklees Council. Yorkshire Wildlife Trust took them over, and recognising that wildlife and farming are intertwined, they are now running the farms quite traditionally with minimal fertilisers. In addition to rearing a herd of beef cattle, they are growing food, and also showing how this can then be prepared and cooked inside the new education centre.
The Building Was Structurally Unsound
After getting in the structural engineers, the existing buildings were found to be unstable. Therefore a lot of work had to be carried out on making the building stand up by underpinning the foundations. The foundations themselves were very minimal.
An artist's impression of the new Stirley Community Farm, courtesy of Eco Arc
Insulation is Put Under The Floor
Bill explains the process of excavating down in order to insulate underneath the floor (200mm of polyurethane underneath a 6-inch concrete slab with the hard core). Alternate 1m by 1m concrete pads are also placed under the existing wall to stabilise it.
Creating a Box Within a Box
As a barn is just an open space, the pioneering approach on which they settled was to construct a timber frame building within the existing masonry. At the same time the existing masonry would be stabilised with the timber frame, and the envelope would be insulated and made airtight. The two structures will then be separated by a nominal cavity. Bill goes into more detail.
A Building With No Windows or Doors Would Be More Energy Efficient!
Bill explains to Ben that you can build a wall to a U value of 0.1 quite easily (which is currently 3 times better than building regulations in the UK). However when it comes to the windows and doors, even using the best components, you might get to a U value of 0.8. That's 8 times worse than the wall next to it. Therefore how that’s installed in the wall is crucial. The frame must be wrapped with insulation from the walls or so that it's continuing the insulation around the frames. They are a thermal bridge in their own right.
Thermal Performance as Important as Keeping The Rain Out
Bill believes we have to look at the concept right from the beginning in a different manner where thermal performance is as important as keeping the rain out. He stresses that you wouldn't want steel balconies cantilevering out of your buildings because steel is one of the worst conductors of heat.
Construction Industry Has an Opportunity to Raise its Game
Buildings of this quality demand attention to detail, and skill and teamwork are more important than ever. This is not the last bastion of a school leaver. It is also an opportunity for the whole team, including the client, to gain a better understanding of what the project is about.
Putting Tenders Out to 10 Builders Will Never Lead to High Performance
Bill suggests a procurement method in which we put out tenders to 5 or 10 builders will never lead to high performance, because the builder hasn’t any ownership over the project. It’s far better to get a builder in partnership during the design stages so they can have their input into the design.
Sources of Moisture
The problem with moisture in buildings can come from several different angles. One is groundwater, which is why people use damp proof courses and so on, and tanking when below ground. There's also moisture from wind-driven rain through a wall, through masonry because stone brick is porous and it has to be dealt with in one way or another.
A Well-Ventilated Cavity Will Avoid Solar Driven Moisture
Solar driven moisture is less well known. It can happen in the summertime and is a danger where you’ve got a radical construction. Once you’ve extremely well insulated internally, the external masonry wall will be colder and it becomes more like a garden wall (lime based mortars breathe, allowing moisture both in and out of the wall).
When you’ve put internal insulation in with a complete air tightness layer, what can happen in the summer when you have a heavy rainstorm is that the wall gets very wet. After that the sun comes out and the heat from the sun drives the moisture inwards. If you haven’t got a well ventilated cavity, that moisture could potentially soak the timber frame inside. There was an example in Belgium where this damage occurred because there was not enough attention to detail during the planning stages.
WUFI
A software program called WUFI allows you work out the minimum air change rate that should be acceptable (in the cavity in this case) in order for moisture to be taken away as vapour. The calculation for this project shows that it is only if the cavity goes below 8 air changes per hour that there is a danger that moisture could start building up in timber frame. In other words, it can be designed out.
Not Practical to Have Every Building With Moisture Sensors
Stirley Farm will have moisture sensors but Bill suggests that it would be impractical to do it on every new building.
Green Building Store's Free Resources
- Denby Dale Passivhaus (completed blog)
- Stirley Community Farm (ongoing blog)
Transcript
Download a transcript of the interview with Bill Butcher.
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3 Videos on Energy-Efficient Homes
Ben has been filming with former podcast guest Martin Evans from the Malthouse Consultancy. There'll be 3 informative videos coming soon.
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