Apparently…

Salix Erectus

The Inside View – Interchange Looking Out

More Salix Erectus

The Glass Group recovering after a heavy night on the town

Lost in Salix

Panels

The crowds gather

Watching Us Watching You

Barnsley does have its charms

Brutiful Barnsley… probably the best 20th Century building in Barnsley

Still changing.. commencing with some minor adjustments

 

Ian’s very conceptual views of Barnsely and the envisioned cultivatable bio-materials structure

Two methods were evaluated for joining these multi-strand willow columns.  The first (below) used only willow and willow ties, staggering the joins of individual poles and adding two ties before and after each join, with additional ties at the start and end of the overall join.

Staggered Joint – 4 willow poles, 4 staggered joints and 16 willow ties

The second method (below) employed a plastic sleeve – a short section of 50mm plastic drainpipe – into which two preformed columns of willow (6 poles each, twisted into 3 groups of 2 poles each) were inserted.  Two M6 bolts were then inserted and tightened to secure the overall assembly.

Sleeved Joint – 6 willow poles, 1 sleeve and two bolts

Staggered and Sleeve Joints Comparison

A triangular panel using willow sticks and PTFE tape – effectively a scaled down version of the rectangular panel we built last week which employed much larger willow poles and fibreglass tape.  Image above-right shows the panel in-tension by means of a wire between the corners at the base of the triangle.

A free-standing structure employing an inverted reciprocal frame using straws and thin nylon coated wire.  A lattice-work frame holds the vertical members in place; a second lattice would likely provide additional rotational stability.

A 36-square chequer test panel frame, approximately 2.5m square,  constructed of willow and adhesive fibreglass mesh tape

Earlier the same day we had discussed the possibility of gridshell type structures using willow.  The small crude test panel I had constructed a few days earlier showed some promise but quickly disintegrated once we had warped and twisted it a few times to examine potential forms.

We wanted to see how much a larger willow framed panel could be deformed without affecting its structural integrity.  Now that we had acquired a larger quantity of good quality willow Fran, Qian and I were able to construct a large chequer pattern willow panel in less than an hour.

Though we had previously tested several joint-making materials (including string, tape and thin lengths of willow) we decided to use adhesive fibreglass tape for this exercise; our brief for this project allows the use of non-cultivatable materials for fixing purposes.

Panel Warping Experiments – no breakages and joints all held

We tested the completed willow panel by warping and bending it in several directions.  There was no significant impact on any of the joints and apparently no significant stress on any of the individual willow members. However, if we are going to consider a true gridshell type structure then we would need to add additional layers of panels to the first.  We would also need to look at how the individual panels would be joined to each other using a method that would allow for easy adjustment and tightening once the required shape had been achieved.  We will also look at alternative methods by which to keep the gridshell under tension.

The fibreglass matrix tape doesn’t slip and provides sufficient flexibility while maintaining joint integrity, even through quite severe bends and warps of the panel.   There was a small amount of unfurling at the ends of the tape after severe test warps of the panel but this should be fixable by application of a small amount of sprayed PVA (which would impregnate the mesh and increase cohesiveness) or the tie of an additional willow wrap as demonstrated in earlier experiments.  Willow ties may well work for the whole structure but fibreglass tape also saves considerable time in assembly, and we are quite constrained time wise!

The key tasks for Monday/Tuesday of the coming week are to look at what materials can be used for infill of such a large panel; additional tests related to shape, form and structural integrity; and planning for the final design.

The 9 sites in Barnsley town centre that will be available for the P5 exhibition on Friday 27th February 2009

Today saw Fran, Qian and me involved in the not often advertised farm activity of Pick Your Own Willow.  Farmer Tim grows Short Rotation Coppice (SRC) willow for use in power generation at Drax power station and was kind enough to let us harvest a very small section of his more than 30 acres near Barnsely (above).  The willow grows to a height of over 4m and is harvested every 2-3 years, yielding about 10 tons per acre.

Select	Cut	Carry & Load

The quality of the willow – even though normally chipped and burned – is excellent, with plenty of long, straight lengths, perfect for our construction projects.  We selected the most suitable willow poles, cut them using long arm garden shears and trimmed them to fit in our transport, saving the off-cuts for more intricate work and for use as ties.  Less than 3 hours after we departed we were back at the Arts Tower with sufficient willow to commence full scale construction tests.

With a small quantity of willow available I decided to spend a couple of hours this evening performing some initial tests.  A square of slightly thicker willow was cut and tied at the corners using sisal (below left).  A matrix of the thinner willow was then laid in a cross-hatch pattern across the frame, alternate ends being laid under and then over the frame (above and below right).  In a future set of tests we will look at additional infill for the test wattle frame – such as brush or straw – and then test applications of a lime mortar mix.

I also tested how willow could be tied to itself (below – left) to create a loop of willow, and used to tie bamboo together (below – right).  In both cases the willow, even though relatively dry, was sufficiently supple that it could relatively easily be tied and knotted.  The joints formed were sufficient for basic connections but would not withstand any significant loading in isolation.

Waterthorpe Infant School Forest Classroom 

Our first stop was Waterthorpe Infant School where Headmistress Helen Stokes was our host for a visit to the Forest Classroom.  The straw bale classroom was constructed in 2007/08 by local eco-builders Hector & Cedric following a requirements led design process between the school and the local community.  Before we went outside to view the classroom Helen showed us a wall within the school where the complete process of requirements capture, design and construction was displayed as a mural of sketches, models and photographs; it was not unlike a pin-up at the end of one of own studio projects although the majority of the budding architects (and clients) were significantly under 10!

Waterthorpe Infant School Forest Classroom: Construction detail showing timber frame (left) and partial infill of straw bales (right).  Photographs courtesy of Helen Stokes

The Forest Classroom comprises a wooden frame and floor raised on concrete blocks to level the structure and keep if from direct contact with the ground. Walls are rendered straw bales – we estimate two bales thick – with circular windows mounted within steel frame surrounds.  The roof is also wood framed with approximately 12 rafters, at a pitch of about 30 degrees, connected to a central circular steel collar containing a skylight.  The roof is covered with earth/turf, presumably over some sort of waterproof membrane.  One final stage of development will see an oven installed so that the classroom is warm and toasty for the tots regardless of the weather.  Even though it is the middle of winter and snow is still on the ground we learnt that two classes had been held in the classroom on the day of our visit.

Waterthorpe Infant School Forest Classroom: Details of skylight, footings, windows, frame bolting and roof

By mid-afternoon we had travelled back towards the city centre for our visit to Heeley City Farm to see a reconstruction – in progress – of an iron age wattle and daub roundhouse.  Sally Rodgers (an ex University of Sheffield archaeology student) is heading the project to build the roundhouse, with support from the Archaeology Department.  Sally showed us the circular wattle wall, constructed using willow on an oak frame, and partly daubed with their preferred clay/earth/straw mix.  Unlike most modern adaptations of similar buildings this roundhouse is staying true to iron age pedigree and does not incorporate any footings or damp course.

Iron Age Reconstruction In Progress: The wattle and daub roundhouse at Heeley City Farm with the wattle wall complete, awaiting completion of daub and roof structure

The roof will be turf on a wooden frame though it will depart from tradition and incorporate a waterproof membrane.  They have also made their own rope – using the road through the middle of the site as a rope-walk – from sisal.  When completed, the roundhouse will be used as a classroom, whilst future plans include the addition of a furnace to smelt iron.

Heeley City Farm Roundhouse: Detail of willow wattle (left) and with daub partially applied (right)

Thanks to Sally for her hospitality and also for the samples of local sheep wool (the farm’s very own), sisal and copious amounts of willow which we somehow managed to squeeze into my car. 

Sally is actively recruiting people to help with the construction, which could entail anything from the gentle manipulation of willow through to throwing mud.  The Heeley site is also home to the South Yorkshire Energy Centre  which promotes energy saving, alternative power generation and runs courses on eco building.

Heeley City Farm: Tinglei, Fran and Qian gathering surplus willow by the roundhouse

Some outcomes of a preliminary group discussion on the project:

> Locally Sourced Materials – Having acquired a quantity of bamboo a discussion ensued about use of local materials and “air miles”.  Though bamboo may be locally available in the UK it is certainly not an indigenous product and the reality is that most bamboo available for easy purchase in the UK will have travelled many miles, though more likely by ship than air.  Oz Clarke is infamous (at least if you watch TV’s Oz and James on their drinking adventures) for explaining that the French word ‘terroir’ can be loosely translated as meaning “a sense of place”, the effects that the local environment have on the manufacture of a product.  Though terroir is used in connection with winemaking I see no reason why it can’t equally be applied to architecture that is produced using materials that are primarily native to the location of a building and that embody some essence of the local environment.  If we pursue this approach then we will need to utilise Long Straw not Norfolk Reed; Yorkshire, not Welsh or New Zealand Wool; South Yorkshire Forest coppice, and certainly no new bamboo!

> Straw Bales – the use of straw bales in our structure will likely depend heavily on a) how many we can get, and b) what transport we have available to get the final structure from Sheffield to Barnsley.  Smaller transport definitely means less straw bales in our design considerations!

Though bamboo may be out if we take a terroir approach it might still have hidden values.  One test we conducted today was using bamboo as a device to attach and fix straw bales to each other.  Inserting the bamboo, across the grain, into a bale was relatively easy but still provided a good anchor on which to affix additional bales or lash external components.

This afternoon we will be visiting a straw bale forest classroom and a reconstruction or a wattle and daub iron age roundhouse, both in Sheffield.