Return of the Cruck Frame - Homegrown and Re-invented

Over 800 years old cruck-frame building is enjoying unprecedented and renewed popularity. Two new buildings – the Sheepdrove Biodiversity Centre and Ben Law's Prickly Nut Wood – demonstrate contrasting contemporary applications to this traditional timber framing method.

Image by Adam Wilson
In the last eighteen months two very different buildings have been completed which are at the forefront of a contemporary resurrection of a medieval building form which stretches back some 1300 years. These two, the Sheepdrove Biodiversity Conference Centre in Wiltshire, and Ben Law's entirely self-built domestic home within his own wooded land in West Sussex, bring elements of cruck-framing into the twenty-first century. Cruck-frame construction utilises the natural curves of the tree, stretching from the roof, down, or significantly close, to ground level. At the apex there is often a ridge beam, so that the cruck-frames, along with purlins and bracing, carry the roof load, thus making the walls' load bearing function structurally redundant. These two new cruck-frame constructions are both variations of an essentially simple building technique, old examples of which remain around parts of the country, a source for a cruck-frame centred renovations industry. They are also vastly contrasting buildings, Ben Law's home uses round wood, while Sheepdrove stays with milled timber. Between the two they span both ends of this part of the timberbuild spectrum.

The Sheepdrove farm building is an ambitious timberbuild project, adapting the cruck-frame to modern engineering. The £2.7 million building is a new arrival on the millionaire and ex-publisher Peter Kindersley's 2000 acre organic farm (one of the largest in the country.) From the exterior the building is neither wildly exuberant, nor understated, a solid eco-pragmatism expressed in it's south-facing L shaped lay-out. Built as a sixties model farm in a hollow in the Berkshire downlands (also a protected area of outstanding natural beauty) Sheepdrove Farm has since its origins, never actually contained a real central focal point, and it was this absence which Kindersley, not a man to do things by halves, decided to address. He decided on building what is essentially a contemporary long barn, to serve as a non-institutional eco-conference centre. A man accustomed to thinking big, Kindersley wanted a building unobtrusive from afar and sitting comfortably in the folded downland, which also provides a sense of drama and expression. The result is a building of timber drama, designed by the Bristol Architects Alec French Partnership and Mark Lovell Design Engineers.

Image by Adam Wilson
The 'visible expressed structure.' or external expression of the 55 metre length barn (the vertical line of the L), is primarily in the long roof, which, because it is supported by the cruck-frame, rises steeply to two narrow flat parallel ridge roof elements. Along the south-face of the barn are a series of three sizeable, rectangular glass window facades, decked with horizontal overhangs to provide protection from the weather. The 55 metre by 30 metre building mixes a layer of Canadian western cedar cladding along the vertical first floor wall, followed by shingle on the roof slant plus further cladding on the upper roof ridge, along with concrete rendering on the building's south face and, more interestingly, a rammed chalk wall experiment along its north side. On the barns' eastern perimeter is a herb garden. One third of the way along the barn, an office complex runs at a perpendicular right angle, completing the base of the L shape. Joining the two, and comprising a two thirds externally visible arc, is a radial turret tower, decked out with a faux pagoda steeple – originally envisaged as Kindersley's eyrie - overlooking somewhat panoptican-like, the main farmyard, landscaped with a pollarded square of trees.

Once inside the dramatic expressiveness continues. What the project's engineer, Mark Lovell, calls a jointed cruck system holds the building together. Four of the buildings twelve vaulted arches are fully visible in the main hall, for conference visitors to admire and relax under. Entering through a ground level entrance under the tower, the main hall opens up to the left and is a large volume, high ceiling space suitable for conferences of up to 200 people. The stand-out interior characteristic is also the core structural feature: the vaulted arches rising high, meeting in the middle (and carrying the load bearing) of the roof.

This modern interpretation of jointed cruck-frame construction, is achieved by a series of four ribs on each side moving from a steep incline to nearly horizontal across the roof ridge, so that, degree by degree, the whole system gradually bends into a deep parabolic half barrel form, mimicking a natural curve in its arc from one side of the building to the other. Because of the arc both columns and rafters are avoided, opening up the space, and drawing together walls and roof as a single structural element. The cruck-frame construction is linked by a series of purlin braces supporting the roof between each vault. The vaulting ribs were designed to reduce the use of metal brackets and rods to a minimum, although each rib is bolted onto the next. Cruck-frame construction was one of three approaches developed by Mark Lovell Design Engineers; Kindersley chose the simplest.

Image by Adam Wilson
The cruck-frame was originally conceived to be constructed from recycled 4.5 metre wharf and mill floor beams. While abundant, according to Mark Lovell, and can be dismantled from disused Northern city industrial sites, they are only a limited range of re-usability functions, being too large for domestic and too small for current industrial build. But after an extensive search the contractor stated that this would be too complicated an avenue to pursue, and the project team reverted to Douglas Fir. 225 mm square these hefty pieces of timber were milled in Northamptonshire, and constructed off site, before being transported to the farm and raised, to comprise the barn's skeleton. The wood for the cruck-frame is Douglas Fir, and the cedar shingles was also originally to be sourced from Scotland, but at the point in the build schedule the right timber wasn't available, so a decision was made to go with Canadian Cedar. The cruck joining system derives from boat construction, borrowing the method for joining a boat between the keel and the prow, a section called the keelson. While the full extent of the cruck-frame vaults are visible in the main hall, providing a space with a calm-inducing sensibility, the Douglas fir sandblasted interior immediately provides something of an old, almost primeval feel. The rest of the building includes a smaller second floor 60 person conference room and a restaurant, where some of the structural material has been hidden away.

Technically, for ventilation, air is piped in at a low level, and leaves at high level, with louvres in the middle so the air doesn't move back through the building, a system developed by Paul Roosevolt at Energy Sustainable Design. Control systems are also used to detect C02, which is monitored from a PDA, and once the control level overruns this triggers vents opening. There is also controlled underfloor heating which can adjust automatically to heat the fabric of the building, for instance, early on a Monday, after being off all weekend. While Alec French's project architect David Mellor acknowledges there's substantial hi-tech equipment involved he sees the building as lo-tech in its general approach. In terms of embodied energy the hardcore is low in cement content. It is the rammed chalk wall, however, with the chalk dug straight out of the ground and compressed into rammed chalk, which Lovell views as the most experimental element in the build, originating in his experience with rammed earth working on the EarthCentre's conference centre with Bill Dunster, though also local examples of downland cob and chalk dwellings.

As another sizeable timberbuild project coming on line the Biodiversity Centre is interesting as a further example of how wide-span timber design can be realised, without resorting to timber columns. Bearing some comparison with the Weald and Downland Gridshell which, after all, is also essentially a barn, and, maybe too, PRS Architects Sheffield Winter Gardens – a glulam structure, even if this latter is essentially a glasshouse - this modern reinterpretation of a cruck-frame in showing how essentially environmentally friendly large-scale buildings can be designed. At the same time, unlike these other two examples, the Biodiversity Centre, as a cruck-frame is part of a very long tradition in British vernacular buildings. This means it predates, and almost leapfrogs the twentieth century revolution towards lightweight structures. Indeed, inside the building the sizeable timbers definitely draws the eye. Lovell argues that this means the building will last, and also contend well with possible accidents. As such, its completion does present a distinct counterpoint to the current trajectory of lightweight timber structures.

Image by Adam Wilson
If it brings renewed interest in cruck-frames, the Biodiversity Centre will be well within a long, long tradition, for cruck-frames are a key part of Britain’s vernacular architectural heritage and history, historians dating their first construction to around the time of the eighth century. Intuitively it is easy to imagine the structural idea could well derive from much earlier times. And certainly other parallel examples, for instance Arctic peoples building shelters from the natural curve of whale-bones, can be picked out from the deep past. In Britain however, cruck-frames were a popular building form through to the fifteenth and sixteenth centuries, for domestic and agricultural buildings, in the main because of their structural simplicity. There are two distinctive cruck frame forms, the full or ‘true’ cruck-frame, and the jointed (or scarf) cruck-frame, although there are at least six derivations of these main two types, defined in part by a variety of joint-forms for bearing the roof load.

The origins of cruck-frames are uncertain, particularly since so few buildings remain from earlier than the 13th century. Timber frame building historians are quite open to the argument that the structural system may have originated separately in several places around the country. The geographical spread is primarily in the west of the country, with true cruck-frames appearing in the West Midlands, the north-west and the west itself, but completely missing from the south and south-east, while jointed crucks are mainly found in the South West; Devon, Dorset, Somerset and Wiltshire, appearing to have originated in Somerset, with some spread northwards up the west coast. Their absence both from mainland Europe and the south-east suggests that cruck-frames were indigenous to Britain. In fact it is likely the influence worked the other way round, with mainland Europe influencing England's most economically and culturally dynamic region – the south-east - with more advanced building forms1. Today there are many remaining cruck-frames across these parts of the country, supporting specialist timber-frame renovations companies. Historically, alongside and as well as the cruck-frame, the much more common and versatile box-frame, continued to evolve through the centuries moving further and further beyond what could be achieved with cruck-frames. By the 1700's cruck-frame construction had become essentially a less efficient and outdated building technique, compared to the elaborations of box frames. As wood supplies rapidly diminished, the cruck-frame faded away, except for a few isolated examples in the north.

Ben Law's cruck-frame at his Prickly Nut Wood home feels much closer to the more usual historical story of cruck-frames. Law's dwelling maintains the traditional and partially medieval link to carpentry as craft, even if, looking from afar at least, it also has definite new age 'natural house' overtones. There are many differences between Sheepdrove and Prickly Nut Wood, but one major contrast is that the scale of the former demands an essentially engineering-centred solution, while Prickly Nut Wood is a carpentry-centred building. A man attracted to living out the beauty of small-scale solutions, Law is a long time stalwart of the Permaculture movement. Prickly Nut Wood applies the permaculture system of working, which respects and partners the ecosystems of the land, as much as humans' needs from the same land, to a woodland context. For those who are not familiar with Permaculture it applies radical agricultural methods to the land, re-calibrating normal agricultural practice so that it is of mutual benefit to both the eco-system and the permaculturist tending it – the aim being to be both ecologically practical and benign. For over twelve years Law has owned and worked 100 acres of mainly chestnut woodlands in the noticeably more rural side of west Sussex. He describes himself as a traditional woodsman, working his particular neck of the woods, primarily charcoaling, making furniture, and coppicing wood for fencing.

After several years of living literally outdoors - in benders and a rusting caravan, Law began to make plans to build his own home from his own wood materials, through the most ecologically efficient lo-tech means; which in effect meant the carpentry-centred craft approach. In 2002 after years of difficulties gaining planning consent, Law and a band of volunteers built the dwelling over a summer period of seven or so months. Law's entwining permaculture with his house building, as well as his prolonged dealings to obtain building permission is explored in full in his book, The Woodland Way .

Two years on and a certain mythology has grown up around the house, not least because the building process was filmed for an episode of Channel 4's Grand Designs series. As a result Law and his house have gained a reputation, albeit on a small scale, well known on the alternative scene which fuels much of Permaculture and associated rural idyll dreamings. When I tried to arrange a visit, Law, asked me not to, stating over 1000 people had visited last year, and he wanted some privacy. As a result, the description which follows is the result of repeated viewings of the Grand Designs programme and conversations with Law and others involved in the building and permaculture, but no first hand visit. It has to be said, I found there was a surreal aspect to watching wholly different worlds colliding in this programme; the intensity of eco-correctness pursued in all its colourful detail through the eyes of the camera and the unctuous, though apparently genuinely bemused, presenter, and on the other hand ads breaking in every twenty minutes for Mazda or Vodafone3.

Given that Law wanted to create his home in and from his own woodland and given that British planning regulations are organised to protect woodland from any building it was initially very difficult for Law to get anywhere with gaining planning permission to build a new home of any type. At first, apparently, it was impossible for Law to get a foot in the door at West Sussex's local authority, to even consider the application. After several years sheer persistence, he gradually wore the dept down, and the planning regulations were finally interpreted flexibly enough to accept Law's argument that his coppicing business constituted a genuine reason to reside on his own land in the wood, and Law's dreams of realising his building began to take on an air of real possibility. The argument that finally won the day was that he needed a home to fulfil his responsibility to look after the wood, as well as maintain his business. However, the accepted application is ring-fenced into his woodland work and he is not allowed to sell the house on, if he stops working the land4.

What is unique about the Prickly Nut Wood dwelling is how, following permacultural principles, the form, design and size of the building are determined by the materials immediately available from within the woodland. Law must have thought about the design for a long time as the floor-plan is exacting, measured out to the inch by straw bales, which are used as the walls main component.

In the early summer of 2001 Law and an assortment of friends and volunteers under initial guidance of carpenter, Viv Gooding, constructed not only a unique roundwood building, but one of the few contemporary cruck-frames built as a domestic home in Britain. Over the length of an early summer day and using eight 30 foot sweet chestnut trunks Law had individually chosen from his woodland, the crew raised four cruck A-Frame's, balanced with a ridge-pole main-beam running the course of the cruck-frames. Following a low tech and low energy impact, Law forwent scaffolding and crane machinery, using a human powered system of pulleys, ropes and a winch to put the initial mainframe in place. Once up, the simple triangular cruck-frame is one of the strongest forms in terms of compression. Using joining techniques that originated, like the cruck-frame, in medieval times, hand cup oak joints, where a cup is carved out, were made. From these well-seasoned, dry dowel heads were cut and manoeuvred into the joins, following this up with a peg to lock the dowel into the join.

With the round wood cruck-frame in place, and looking something like an oversize triangular Toblerone bar skeleton, the building team began laying the floor and extending the veranda outwards. At the same time the frame was strengthened with a cross brace system of hand chosen diagonal sweet chestnut direct from Laws' coppice, each piece individually chosen for the appropriateness of shape as well as an intuitive sense of character. Peeled of bark, these were cross-braced between each of the four Cruck A-frame sides. For the roof a water proof membrane along with rafters, preceded a heavily overlapping shingle roof, composed of 12, 000 individually cut and pre-drilled shingles (to avoid the danger of splitting), which Law had prepared over the preceding months. This method of preparation had been used across the channel on continental Europe, "for years," and has a life expectancy of forty or so years. The chestnut gives the roof a strongly matted, textured feel and in time will turn grey. The next step was to install Warmcell insulation, a 'breather' membrane, and 300 16 inch straw bale walls, as further wall insulation bought from a neighbouring farm. Since the house had been measured in bales, each section of bales slips in exactly between the studwork frame, like a carefully composed kit. The windows, therefore, are bale height. Internally the plan's design provides a bedroom, open kitchen-living space, and bathroom. Externally, Law next applied 'wavy' edged board over the studwork, before digging out clay from a pond within his woodland, mixing it with water, sod and straw to make up plaster, which he filled in over the straw bales. Lastly he added the windows, a large arched front window, further windowing on each side, including three roof windows which allows the main room, with its ceiling free, open cruck braces, to flood through with light. All these window frames were personally built from coppiced as, with their catches made of yew, There is a Rayburn, an organically shaped clay cob fireplace and his bedroom is painted a restrained red, a mixture of iron-oxide and turmeric.

Outside the house is an array of solar panels, previously redundant after their life cycle ended on TV's Big Brother programme. These supply half a kilowatt of power, stored in ex-submarine 2 volt batteries; enough to run Law's lights, laptop and stereo independent of the grid. Law originally estimated a budget of between £20 and £25, 000. In the event the price overran to £28, 000, because of an under-estimation on the glazing. From the television programme the (almost) finished home feels very much in architect and the EcoDesign Association founder, David Pearson's, 'Natural Home' mould, and the appeal it has attracted amongst a curious public makes sense. Indeed Maddy Harland of Permaculture magazine describes it as the most 'natural house' she has stepped into. Not only this but Law has lived out his dream, something many of us have a lot of time for.

Indeed, there is an intense idealism to Law’s Prickly Nut Wood home, and it is a remarkable achievement and show of perseverance to stay with a project that initially seemed so unlikely to be permitted. That it has done provides an appealing example of a pure and unadulterated ecological way of living and being, which addresses many issues about rural living, and inspires thoughts about the possibility of a future for woodland communities. Patrick Whitefield, one of the best known practitioners within the Permaculture community and author of How to Make A Forest Garden, acknowledges that, pragmatically, it is not a path open to everybody, although he comments that it could one day possibly become a mass building. He ponders whether six further buildings may be being constructed on the basis of Prickly Nut Wood’s sphere of influence. Quite possibly. Law refers to two other cruck-frames, he knows of; one at the Greenwood Trust in Shropshire, the other by Mike Abbott of Living Wood in Herefordshire. Law says he, “would like to think that it’s the start of a re-emergence of cruck-frames”, although he points out that Prickly Nut Wood is primarily a showcase for chestnut as a ‘large durable timber’, given the prolific chestnut roundwood found in the south-east, rather than being about cruck-frames in themselves. Whitefield enlarges on the context, stating that Permaculture is ‘a minority amongst minorities’ and contra-indicated to the current economy, while organic farming is demonstrating itself relatively well suited to modern ‘natural capitalism.’ Whitefield believes Permaculture will come into its own in the future, by implication a future where things have changed. Law’s building can be said to bring the practice of Permaculture into the living room. In setting the precedent, Prickly Nut Wood is suggestively provocative about all sorts of possibilities for future rural-forest living. Certainly it is a significant addition to the repertoire of examples of, and also the debate about, rural living in the early twenty first century, in terms of chestnut as a sustainable material, the practical application of Permaculture principles, and another strand in the greenwood forest community story begun by John Makepeace’s 1990’s Hooke Park project, and presently being taken a next step by the Flimwell Woodland Centre in the east of Sussex.

From another perspective the apocalyptic vision which Permaculture integrates into its story about itself, is alien – and arguably somewhat alienating - to much of contemporary society. My sense of Permaculture, and Prickly Nut Wood as a building analogue of Permaculture, is that the movement appears to exist in a parallel universe, where the contemporary consensual hallucination known as 'reality' has somehow been made to unhappen. The implied tenacity of Law's dwelling, its duty to example, fuels a sense that catastrophe is not only upon us, but has already passed by sometime ago, Law's project is post eco-apocalypse survivalism in action. But, then again, maybe it has. It is interesting that Permaculture is almost an, albeit off the map, alternative to Organics. As Sheepdrove is future oriented organic farming and natural capitalism at full tilt, so by extension the Biodiversity Centre is to Future Organics what Prickly Nut Wood is to Future Permaculture. Not only this, but the one rules out the other; you couldn't build the Biodiversity Centre using the principles applied at Prickly Nut Wood; the latter would not be what it is if it had used the building principles of the former.

Prickly Nut Wood is a contemporary vernacular of the cruck-frame tradition, and completely medieval in values, give a solar panel factory here and a computer plant there. Sheepdrove is also medieval, but a different medievalism. Law talks of his home as a temple to wood, and Mark Lovell uses similar 'new age' inflected language about Sheepdrove, words like 'ecclesiastical' and 'purity.' But the Biodiversity Centre also contains elements of modernity in its millennial medievalism; both industrial engineering and a streak of real-politic running through it. This suggests that in this specific sub-current of the architectural realm, as in the wider cultural sphere, as Umberto Eco pointed out, there are a multiplicity of medievalisms' still diversifying and cross-fertilising6. If this is the case expect to see further cruck-frames both on the drawing board, and literally going up before your eyes.

Yet while there are differences, each are, albeit different, ways of doing building. The difference may in the end come down to money, a rich man/poor man divide. Whether the earth can sustain the economics which facilitates a Sheepdrove a hundred years from today, or will of necessity and Climate Change be plunged into the kind of future Permaculturalists foresee encapsulates the question which separates the two.

This is a version of a piece which was published in Building For A Future