The Crab House is made from Scottish Douglas Fir. There is no concrete beyond the foundations, she’s all wooden and we built her between 2011 & 2013. The main structure is a cavity system and was manufactured using CNC technology and erected as a shell by Rayne Construction Ltd. I fitted out the house and built both glass ‘claws’.
The Crab House is my interpretation of a ‘total-Life carbon zero building,’ but has it reached that status? Probably not.
When we designed the Crab House, my Wife Charlotte wanted the internal layout to be of her own, the house should work to our way of life, not the other way around. We both wanted the house itself to BE art, highly efficient, functional, responsible, cheap to run and where ever possible, design it to make us feel good.
We’re not architects but property in general has been our living and I have always been interested in architecture. It was important to me that the Crab House should not be limited by the doctrine of ‘modern’ architecture, but should instead look back to an earlier ethos of aesthetic style first. It appears we’re not alone in this thinking. Judging by the number of public who seek us out and by those who stand at the gate to take photographs, ordinary people love it. During the tourist season, small crowds gather to look on, it does seem to please. The overwhelming sentiment of these strangers is that they see an entirely natural, uplifting art form and harmony between the Crab House and its environment, something I think, almost impossible to achieve without wood.
I know what you’re thinking; ‘it’s alright if you have the money’. Well, in fact, it was no more expensive to build an arty house in timber than it would have been to build a boxy one in concrete block and steel. The Crab House is about 175m2 and cost £240,000 finished including the land. It’s worth noting that the plot on which it is built is second rate. The Crab House is not a dream house it is a realistically attainable one. Nevertheless, my friend and neighbour coined it ‘timber triumphalism’, he was pulling my leg at the time, but my friend obviously knows me too well because, I rather like the term.
Our mantra has been; Science, Art and Living. The Crab House relies on very simple and reliable science, there are two fundamentally important factors. Firstly, the structure is solar aligned and we exploit the Sun’s parabola every moment the Sun shines and from which we derive both heat and light. On Scotland’s East Coast, surprisingly, the Sun is present a great deal of the time.
Secondly, the Crab House has no thermal mass, it is intentionally a light weight structure. This means that when the Sun shines, it only has to heat the air trapped inside the living space and crucially not the fabric of the building. Air conducts the Sun’s heat rapidly and so the temperature in the room rises rapidly. The effect is rather like your garden green house. In our case, and depending on conditions, it takes only 20 minutes to 1 hour of sunshine for the Living space temperature to rise to 250 C. Unlike your garden greenhouse, the Crab House is basically airtight and so the temperature gain takes a very long time to dissipate.
In my experience, a light weight structure is so much better suited to our Scottish Climate. Whilst the Sun is present a great deal of the time, it is rarely out for long periods of time and so our two fundamentals above, are designed to cope and exploit the conditions without the need of any mechanical devise. In other words, free heat and light.
So, what’s it like to live in? The living space is on the first floor and the bedrooms and bathrooms are on the ground. We maintain a Mediterranean climate year-round in the living space with a temperature between 25o C and 32o C and it is bathed in natural light and sunshine. And no, it doesn’t over heat but you do get an extremely dry hot heat that warms your very bones, even when it is sub-zero outside. The bedrooms stay between 18o C and 20o C.
Unlike the much-publicised short comings of Passive Haus, we have never suffered any condensation or mould. I think this has a lot do with the fact that the house is wooden.
I’ll get to the point of why I’m telling you all this shall I?
The Scottish Ministers commissioned a report published in 2007 called ‘A low carbon Building Standards Strategy for Scotland’. The report is commonly known as the Sullivan Report which was updated in 2013.
The Sullivan report recommends that new buildings should be ‘net zero carbon’ by 2016/17 later extended to 2019. The net zero carbon only relates to space and water heating, lighting and ventilation.
However, what is more interesting from a forestry perspective, is that the Sullivan Report also recommends ‘Total-Life zero carbon buildings’ should be achieved by 2030. This means that new buildings should be responsible for net zero carbon emissions over their entire life, including construction (the embodied energy of building materials), use, maintenance and finally demolition.
I am not an expert but based on my experience, to get to a total life zero carbon building you need a whole lot of timber. The Sullivan report does state that a ‘fabric first’ approach is best and then adds that ‘layering’ and ‘allowable solutions’ may be added. These terms seem to relate to environmental schemes which affect the common good rather than specifically the buildings to which the Building Warrant refers. On first reading, this sounded a rather lazy way to solve the problem but I’m suggesting ‘layering’ could be an opportunity for Scottish Timber.
The Crab House is my interpretation of a ‘total-life carbon zero building’ but whether it is or not I’m not clever enough to work out. The National Calculation Methodologies are, (again in my experience) insufficiently sophisticated. When we applied for our Building Warrant, the Methodologies discouraged the use of electric water and space heating probably because the assumptions were based on out of date electric technology.
I applied the following simple logic; The Crab House’s primary source of heating is the Sun, 100% emissions free. When there is insufficient sun, we have a more than adequate 3kw wood burner in the living space. We have a very modern hot water tank and electric immersion heater for hot water. As a backup heat source, there are also three ‘21st Century’ electric heaters on the ground floor and two 500watt bathroom heaters. The 21st Century heaters are 100% efficient, have zero emissions and are fully controllable. Crucially they can be turned off for months or even years at a time seemingly without detrimental effect. In very cold conditions we do use them to raise the bedroom temperature from an ambient 18o to 20o.
My point being that to reach the zero-carbon target, our system gives off no harmful emissions, requires no maintenance (except sweeping the chimney) or annual servicing and no storage of filthy oil or highly flamible LPG.
According to the BBC news, during May 2017, Scottish wind turbines alone produced enough electricity to supply 95% of Scottish homes. PV panels during May additionally produced enough electricity for over 100% of Scottish homes.
Also, although the Methodologies make an allowance for solar gain, as I have explained, the effectiveness of solar gain is dependent on the performance of the rest of the structure. In my experience solar gain has a wide spectrum of effectiveness, our system being at the most effective end of that spectrum.
I’ve not found an accurate method of calculating the CO2 sink inside our Douglas Fir, or how (or even if it’s allowable), to offset it against the CO2 created by the concrete foundations.
When deciding if an all timber building meets the classification of Total -Life Zero Carbon, the calculations are, I assume, made on the hypothetical final date of demolition. If it is further assumed that the timber fabric has been allowed to simply decay as a derelict structure, (and not reused), and thus the CO2 sink allowed to disperse into the atmosphere, then there is no relevant off set, against the concrete foundations.
However, I hope the process will take account of the life expectancy of a structure. There are many examples of British timber framed dwellings that are still in use over 500 years after they were first built. In the case of the Crab House, it has been built to last. It is perfectly reasonable to assume, the Crab House is capable of lasting as long as those of the 16th Century, (subject to cladding replacement), and it will provide its occupiers with the majority of their heat and light courtesy of the Sun, free of charge and free of emissions throughout that period. We’re talking a substantial financial saving and one hell of a carbon emissions saving too. It is my believe that by building a structure that is aesthetically pleasing, responsible and built to last, then you build a legacy.
I’m advocating that when calculating the carbon emissions of a legacy building, the calculations should, perhaps include a recognition of the fact that no replacement structures will be necessary for at least 500 years and for the legacy recognition to be an allowable solution to off set against the initial concrete foundations.
That is basically my case for Total-Life carbon zero, or will be when mains electricity generation is more renewable. The Crab House methodology is intended to bring the ‘Eco home’ into the mainstream and suitable for ordinary people as opposed the elite that charchertrise Eco home owners to date. The Crab House methodology is realistic, practical, reliable and there is no requirement to factor in the heavy cost of replacing PV panels, boilers or wind turbines every 15 to 20 years which quite apart from the financial issue, is a significant (manufacturing) emissions saving too.
From The Whole House book, (CAT).
Timber is the only renewable structural building material, Timber has a low embodied energy compared with other structural building materials.
Because growing trees absorb carbon dioxide, harvested timber can be seen as a carbon sink, locking up the CO2 which the tree has absorbed, until it is burnt or rots away. One kilogram of dry timber contains about 50% carbon, which binds in 1.8kg of CO2. If the forests that are harvested are then replanted, timber becomes a carbon-neutral material. The growing tree will take up as much CO2 as the harvested one will eventually release.
In general, it is easier to achieve higher insulation values, and therefore lower energy use, with a timber construction than with a masonry one. It is difficult to increase the cavity depth in a masonry wall substantially, without extra-long ties or additional structural support. As the Building Regulations call for higher standards of energy efficiency, so contractors and developers are turning to timber frame construction to minimise extra works and cost.
Now, if Scotland’s construction industry gears up their timber content by 2030 (Brexit may or may not change everything), can Scotland’s woodlands take every advantage possible from the potential higher demand. My guess is that 2030 is too ambitious. The Sullivan Report also suggests the rather quaintly named compromise of ‘nearly zero carbon buildings’ as more achievable. I doubt there will be many all timber new houses, but the solid timber content must surely rise.
My contribution to Scotland’s forestry future is to suggest that all Scottish timber sold for construction should be recognised not only for its own inherent CO2 sink and replanting management plan, but automatically be given an additional ‘layered’ overage justified because of the obvious upstream environmental benefits for rural Scotland.
Ideally, perhaps there could be an industry accepted clever software that would accurately calculate the carbon sink by entering volume, species, miles traveled, processing and layered environmental overage. Architects and designers could then be presented with a credible certificate for using Scottish timber over imported alternatives. I imagine the distinct commercial advantage I suggest would be contrary to European law, but do we care about that anymore?
In conclusion, it seems to me that the devolution of forestry, zero-life carbon construction, Brexit and the enthusiasm in Scottish Forestry are all coming into alignment.
Finally, I’m sorry to sound so cocky, there is a downside, the Crab House is hardly maintenance free! I’m also well aware that the Crab House is not the ultimate in Eco design. I hope that others will find it a useful springboard from which to design and build better.
For centuries art and ornamentation has been used in architecture, I’m on a one-man crusade to reintroduce it.
This article was first published in 'Full Circle' magazine, issue winter 2017.
'Full Circle' is a Scottish Forestry magazine.