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Wow! What an amazing week - sunshine, fun, creativity and adventure!

Wow, what a busy week we've had at Eden's Forest Holiday Club! We spent the week making knives and forks, atl atls, willow lanterns, samurai swords and even a giant catapult the Romans would have been proud of!

We have just completed a series of 5 days working with the children at Rowley Lane Primary School in Lepton.

The school's PTA had raised some money to improved the outdoor play areas of the school. They asked Eden's Forest to develop an idea for willow structure adjoining the playground. We proposed a sea theme where a giant willow fish was being persued by the reaching claws of an even larger willow crab. The school and PTA loved the idea and asked us to proceed.

In early 2014 we began a project with Scholes Primary School near Holmfirth to create a class-sized Celtic roundhouse.

The intention was for the children to build it under instruction, and that it would be as authentic as practically possible. The children would learn how to map out and level the building site, safely move and position large timbers, to use the tools safely to work those timbers and to problem solve the building process. Ultimately they will have an outstanding, hands-on learning opportunity and an all weather outdoor classroom large enough to accommodate at least 30 children.

This blog catalogues the planning and building process, warts and all...

If you would like us to facilitate a similar project with your children, please get in touch.

Jerome & Adam

 


 

January 2014

The planning has begun...

After great consideration, we have opted for an octagonal set of upright posts, linked by their tops with a ring beam. This ring beam will carry the weight of the rafters which will form a conical roof. The roofing material has yet to be decided. Wheat straw thatch is currently £800 a tonne so not viable. Turf stripped from the site is a sustainable option but has structural implications due to its weight when saturated. We have opted to leave the roofing decision for the time being and proceed with the structure.

Below are two images of the plan and side views proposed. Final dimensions will be a function of the available timber:

Plan view  Side view

 


 

February 2014

Through various contacts and our wonderful tree surgeon Lee, we have managed to source all the wood we needed.

The uprights will be oak with ring beam sections of oak, beech and (very thick) hazel. The rafters were intended to be ash due to its strength and straight nature, however a very generous benefactor has offered us some wonderful sycamore which is more than up to the job.

We have surveyed the site for the build and agreed that there will need to be a 5m square platform levelled with a small amount of cut & fill. The turf will be stacked for either the roof or a turf section of wall.

Lee helped us deliver much of the necessary wood to the site so we were ready to go once the school is ready.

Here are some images of the location and the timbers ready for use:

         IMAG0665   IMAG0669

 


 

March 2014

Groundworks have now begun!

The site is slightly sloping so needed levelling. Moving earth onto established turf creates a discontinuity making the ground unstable. To prevent this a 5m x 5m square was stripped of turf ready for levelling. This was very hard work - particularly for one person (Jerome!). This kind of simple manual work is perfect for involving the children, however we decided to get the donkey work done before the children joined us. This means that the results on the ground will be quicker for the children to see. Here are the results of Jerome's labour this week:

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Once the turf was finally removed, the top of the slope was cut and moved to the lower slope. Although this did not create a perfectly level site, it was considered close enough, particularly by Jerome who did all the digging!

IMAG0740 Before levellingIMAG0741

After levelling

For those who are interested in the technical bits, the next job was to mark out the appropriate area for the roundhouse as a regular octagon. The octagon was chosen as a practical compromise for a series of posts to demarcate a circle. They provide a series of straight sides connecting the posts to create wattle & daub walls, but once the roof is on, they will give the appearence of a circular structure.

The 5 metre square was deliberately oversized to allow a wood-chipped surround for drainage and improved access. This square however was too large as a basis for the structure as our timbers were not long enough.

Although the concept drawing above gives different measurements, we opted for a diameter of 3.5 metres which gave spans of 1.5 metres - perfect for our timbers, and still large enough for a class of children.

Below are the three stages moving from a 5 metre square to a 3.5 metre diameter regular octagon:

Spec 1

Here, adjustments are made to insert a square of the correct dimensions. Once the square is marked out with pegs and string, the centre is located using the diagonals. This allows the radius of the arc for the next step to be measured.

Spec 4

A peg and string was used as a set of compasses (measured as the length from the square's corner to centre point). The string created a series of arcs from each corner intersecting the square's sides twice each time. Each intersection marks one corner of the octagon, and one of the upright posts as seen below:

Spec 3

 Things moved on significantly following our first day with Year 5. The children worked hard to solve the using and applying problems we gave them e.g. find the centre of this square, mark out a 3.5m square at the centre point, create a series of arcs to locate the corners of a regular octagon etc. They really did themselves proud. Once the marking out was completed, 50cm post holes were dug at each corner to receive the eight uprights.. Each of these uprights had 50cm of their sapwood removed at the base to reduce the impacts of rot.

The shortest of the uprights was placed in the upslope post hole, then this was used as the level reference point for the remaining posts. The other posts were cut slightly longer than needed so that once the eight posts are in, a spirit level line can be used to chainsaw the tops to exactly the correct level. Alternatively, we may use the Roman system of levelling using a long tube of water.

Below are some pictures showing each of these stages and where we got to by the end of day one with the children.

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3.  DSC07949

1. Pegs marking the octagon.

2. Working the timbers by hand.

3. Timbers lined up ready for preparation

4.  DSC07950     5.  DSC07951 

6.  DSC07952

4. Adam working hard on his axe technique. 

5. Locating the shortest post as a reference point.   

6. Post in place before tamping with stones and soil.

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Adam showing the likely roof pitch and apex height

In the next session we continued to work the timber uprights and install them in the post-holes dug by Year 5. Each post had stones rammed down around them and soil packed around the stones until the posts were solid.

 DSC07986 DSC07988    DSC07989

Once the posts were in place, a line was strung from the top of the lowest post around the other 7 uprights. A spirit level was used to ensure the string line was level. This was used to mark the cut level of the uprights so Lee could come in with his chainsaw and cut the posts level.

DSC07990 DSC07991 DSC07993

The cross members were then laid out so that they could be measured and cut to length. The length was defined by the distance between each post top with a small overlap (~2") at each end to ensure the cross members would overlap each other. The overlapping ends were marked and cut with a handsaw to half their depth. A bill hook and mallet were then used to split the timber back to the cut.

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A bit & brace hand drill was used to drill peg holes, and hazel pegs were used to secure the cross members in place. Once the ring beam is complete, discrete timber ties will be used to ensure absolute stability.

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To aid access for adults, an arching piece of hazel was found to act as a the entrance cross member. In addition to this a porch will extend out around 3-4 feet. 

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Here is Magda helping to choose the correct timbers for the cross members...

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April 2014

After some thought we adapted the approach we were taking with the ring beam. Each alternate section was fitted with peg fittings facing upwards. This was a straightforward process requiring very little adjustment to the timbers. Having completed the alternate upwards facing cross members, the downward facing timbers could be adjusted to fit the structure and then pegged.

    DSC08030                        DSC08031 

   Upward facing timbers awaiting a neighbour                     Due to more headroom than planned, the arched

                                                                                            entrance beam was removed to form a porch and

                                                                                                       replaced with a horizontal beam

As you can see below, each timber end was hand drilled with a brace & bit by the children, then pegged into position with hazel pegs. These pegs were really only to locate and line up the timbers rather than to provide long term fixings. Next to each peg, two 8" timber ties were drilled in discretely to provide a secure fixing.

                                                   IMAG0766                                      IMAG0770

To finish off the week's work, the arched timber was positioned in front of the entrance to form a low porch. The children measured the location of the post holes, dug them to the required depth and stripped the turf. The posts were inserted and made secure with rocks and soil tamped down securely.

 IMAG0769

Porch and uprights lined up ready for installation

   IMAG0772

                            Porch in place ready for the connecting structure to be added.


 

May 2014

As we moved into May, it was time to get the roof on. On paper the theory is fine, however working with timber above head height with children adds a complexity to the logistics and safety aspects that require careful consideration. Tasks needed to be age appropriate, group size appropriate and the safety briefing had to be adjusted accordingly.

Roofing timbers were measured by the children on the structure using a long easily manipulated piece of hazel. This was then laid on the ground as a measuring stick and potential rafters were offered up and prepared one at a time. A tripod was constructed using square lashing at the apex. The tripod could define the finished roof apex by adjusting the pitch of the the tripod's legs. Once the tripod was in place, a stoud hazel cross piece was created (a little like a cart wheel without a complete rim) so that each rafter could be secured just below the apex. With the children working as a team, each prepared timber was presented to the ringbeam and pushed into it's final position. Held in position, the rafter could be securely fixed to the ringbeam and the top cross piece.

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Magda enjoying some fresh air.

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Mrs Knowles sorting out the long timbers

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Buiding the small cross piece to secure the apex

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Hazel cross members forming the extended porch

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Here you can see the temporary tripod to rest rafters on until they can support each other. In the centre is suspended the cross piece to which each rafter will be secured. In the image on the right you can see one rafter in position. This was notched into the ring  beam, timber tied at the ring beam level, then fixed to the cross piece at the apex.

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Adam working with Year 5 to secure hazel to the porch roof

 IMAG0805

Here you can see the second rafter in position on the left

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  By the end of the day we had made great progress. The porch roof was ready for weaving with more slender hazel or wilow prior to thatching and two rafters were in place, ready to receive the remaining 14!

This week the weather was dreadful. Jerome arrive early to put the parachute over the structure to keep off the worst of the torrential rain and strong winds. Despite this the decision was made not to include the children this week. This was partly as cold wet children do not generally engage with the work, but also for safety reasons - we were going to be working on parts of the roof and as the wood was wet and slippy it would be sfaer and easier to manage with just the adults.

        IMAG0826      IMAG0829 

     IMAG0834      IMAG0835 

                        Here you can see the cross piece, and hazel square in place at the apex.

IMAG0836

Here is Jerome showing off / testing the structure - it depends on whether you ask Adam or Jerome! 

We had an entertaining day resolving the structure at the apex of the roof. Cable ties were used in the first instance as a quick and safe way to secure timbers in place until permanent fixings could be fitted. Each of the four principal rafters were secured to the apex cross piece, and to each other at the very top. Once this was done, the supporting tripod could be removed as the roof was self-supporting. Finally four lengths of hazel were secured in a square around the outside of the rafters. This was rather 'belt and braces' but ensured there was no flexing or twisting at the apex. At this point the remaining rafters had a stable and secure structure to be fitted to. It took about 5 minures to measure, cut, and fix in place the fifth rafter, so we expect the rest will be equally quick and much more straighforward to do with the children.

Once again the weather was determined to make life difficult for us at the end of May. Despite this, through torrential downpours we managed to complete and secure the 16 roof timbers. Each rafter from a column top was secured at the apex and to the central frame. Each intermediate rafter was cut slightly shorter and secured to the central frame. This prevented the apex becoming too crowded.

025 026 

028 029

Once the rafters were in place, a piece of string was used to mark a roughly level line for them to be cut to length. Some were already the correct length (or a little short) but most were fitted deliberately long and needed trimming.

030 031 

The final job for the day was to secure the lowest hazel horizontal bar between the rafters. This was screwed into place with 75mm screws as it was bent between each rafter end. This was to serve as a ladder rung for older children to continue wrapping or weaving hazel on the roof.

035 036 037

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Loading up with hazel and willow for a day's hard graft.

 IMG 0179    IMG 0180    IMG 0182 

The view from the roof with Mrs Knowles.


 

IMG 0185

The state of play by June 2014. The rafters are in and secure. The children have begun weaving willow sections of wall for the porch and scuring hazel horizontals on the rafters. There still needs to be much more hazel added to the roof - the more that is added the safer the working environment for the children on the roof. It almost becomes a conical ladder system.

 

IMG 0186    IMG 0187


 

As September came around we looked into the proposed bracken thatch. There was some concern about bracken spores so I did some research. It seems the bracken can release spores as part of the reproductive cycle towards the end of summer but only during a spell of very dry weather. Consequently large scale releases of spores are not frequent. We opted to harvest as the bracken was turning at the beginning of Autumn and the reproductive cycle was clearly over.

We found a land owner who wanted their bracken clearing. This seemed a good way as the plant as a whole is removed rather than sprayed or cut back to come again next year. Jerome is now regretting this as a thatching resource, not least because it is extremely labour intensive. Having had two good days harvesting and thatching, a reasonable estimate for the whole roof is about 13-17 person/days! If you can get a good gang together, all the better!

Tip: When harvesting the bracken, pull from the folliage end to prevent the stem breaking near the base. Breakages are not wasted but the integrity of the thatch is better if the stems are unbroken.

IMG 0801 IMG 0802 IMG 0803

 Here the bracken has been pulled and tied into small bunches. Once on site a simple hazel needle was made to 'sew' the bundles onto the roof framework.

IMG 0830                             IMG 0831

James and Jerome learnt on the job sewing and tieing the bundles into position for the first layer. Believe it or not, what you can see here is about 2-3 hours hard graft harvesting bracken. Once trimmed and sorted you don't get much for your efforts!

IMG 0912 IMG 0913 IMG 0914 

We found after a couple of weeks on the roof there was a lot of shrinkage in the bracken. This inevitably resulted in gaps to be filled and slack in the twine used to tie the bundle. Rubber ties may fix this for future bundles. Watch this space...


 

I am now cursing myself for suggesting bracken as a thatching material. It is of course free if you can find an obliging land owner, but it is unbelievably labour intensive.

To get a handle on the scale of this, I conducted an experiment:

In a 4.5 hour period I harvested bracken alone and made x50 bundles, each containing 40 stems (these filled the back of my Landrover once trimmed of the bushy end). That equates to 2000 plants pulled by my own fair hands in one day. I was extremely pleased with myself until I put them on the roundhouse to find they covered about 6 linear feet. Using this as a guide I have calculated that the entire roof will need approximately 20,000 bracken stems. This equates to 45 person/hours to harvest, plus processing, transport and thatching time!

The upshot of all of this is that we have run out of time this season. The bracken that is left is mainly collapsed and rotting off now, so we have come up with a solution to see the roundhouse through to next Autumn - a parachute!

We have almost completed the bottom lift of bracken (using around 10,000 plants) and we intend to secure a parachute over the un-thatched roof area so that the school can make use of the roundhouse during poor weather. This also means we are able to complete the wattle and daub wall sections without the rain destroying them.

IMG 0939 Adam trimming yet more bracken!

IMG 0941 Making slow progress around bottom lift of thatch.

The state of play as winter sets in (although the lower lift of thatch is now complete):

IMG 0965

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It's been a very busy start to the new year!

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