A few years ago I was shown round a state of the art home, designed, the owners informed me, to be ecologically friendly. They had a ground source heat pump but I was not convinced that the efficiency gains from this would counteract the expense of heating all the rooms with north facing glass walls. The bath carved out of a rock from Bali was beautiful but made me wonder just how much hot water it would take to warm up such a massive natural heat sink.
After two years of planning, sourcing, contracting and building we have finally finished our own eco build project- a substantial extension to a small listed gatehouse. It does not look particularly green. There is no wind turbine, no heat pump, no solar panels. We considered these options but given the location of our house, the benefits didn’t go far enough to balance out the embedded carbon and other environmental costs. Instead we have focused on more basic technology and simple science principals to guide our decisions on everything from room layout to materials to colour choices.
Structurally it’s basically a polystyrene box with a wooden frame. The lightweight materials mean less concrete in the foundations. Cement production is a big source of carbon emissions. Without windows, the extension would be so insulated that we could heat it with our own body warmth. Glass is a poor insulator and even good windows (we have gone for triple glazing with a low e coating and Argon fill) leak heat, so we have gone for fewer windows than found in many modern buildings. The exception is the sunroom which has a south facing glass wall. This is great when the sun is shining but leaks heat when it’s not, so we have large sliding doors partitioning it from the rest of the building. Our polystyrene walls are great for insulation but useless for storing heat, so our sunroom has a dark slate floor and a plastered stone wall (part of the original building) that we have painted a darkish colour. The slate and the wall will absorb and store the heat from the sun.
We tried to use local or recycled materials where possible. The slate in particular presented a sourcing dilemma: the price of slate is inversely proportional to the distance it has travelled, with Chinese or Brazilian being the cheapest. In the end we went for Welsh, but this was tricky to source and was the element that held the whole project up. Our architect had some reservations about our other flooring choice: maple boards recycled from a school gym floor (complete with games court lines). But the engineered joints were still good, it was straightforward to fit and looks great. It was also much cheaper than new wood flooring of equivalent quality. For our rainwater harvesting we bought a 120 gallon oak sherry barrel, for a similar price to the plastic equivalent. On the cladding, aesthetics got the better of us and we fell for the look of red western cedar over larch. This was a problem for us since most cedar is sourced from Canada or Siberia, whereas Scottish larch is locally available in abundance. We were overjoyed therefore when we got a message from a friend who owns a sawmill in Ardnamurchan- he’d just got 50 tonnes of cedar from a local road clearing exercise- were we interested? We jumped at it.
Ultimately the eco-credentials of our house will depend on how we use it. I’ve bought a timer with an alarm, set to go off if I stay too long in the shower. We don’t intend to use our sunroom on winter nights and cool overcast days. I work from home, but during the daytime any heating will be limited to my small study, which like the sunroom has been designed to maximise passive solar gain. And when that fails I will resort to the tried and tested green technology: woollen underwear.
A picture can be seen here.
Ruth (guest blog by a member of my homegroup)