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7/27/2019 Roundhouse Paper

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How to Build an SCA Practical

I ron Age Celtic Roundhouse


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In an attempt to add a more period feel to our camp, my fiancee and I decided tocreate a more authentic Celtic dwelling for us to live in at camping events. The first

thought was to find a period Celtic tent design, and replicate it. After extensivesearching, we found nothing useful. It seems that the Celts were not big weekend

campers. There are some Roman tent designs from our time period (1stcentury A.D.),

but we wanted something more Celtic in appearance. During a trip to Butser AncientFarm in Hampshire, U.K. we saw interesting Iron Age Celtic roundhouse reconstructions

that fit the bill quite nicely (see Appendix 1). The goal then became to replicate theroundhouse look, with something that was portable, roomy, and still structurally sound.

The prominent details that I wanted to incorporate in the tent were that the roof shouldoverhang the walls by a fair amount, the walls should be relatively short, the roof shouldhave a peak at the top, there should be an entranceway that sticks out of the front, and

that there would be no center pole to obstruct the usability of the inner space. I decidedthat a tent with a wooden frame and canvas skin would be the way to proceed. After

investigating many alternatives, it seemed that a tent that used many of the constructiontechniques of a Mongol Ger (popularly referred to as a yurt) would be the most efficientand functional method to pursue. My first step in making a roundhouse was to decide

what size tent we wanted to make. Although this description could be adapted to makepractically any size tent, we decided to make an 18-foot diameter structure, with a 12- foot

peak. We thought that this would be a comfortable living space, and also be big enoughto entertain people inside when we chose to.

There are five major portions of the roundhouse that need to be made. These are thelattice wall, the roof rafters, the roof ring, the doorway, and the canvas covering. I will

explain the methods I employed in fabricating each of these different parts in thefollowing sections.

1 Wall Lattice

1.1 CalculationsIn making the lattice, you have to figure out how long and how high the wall would

be. The length of the wall is determined by the circumference formula minus the widthof the doorway. Since the diameter is 18, the circumference can be found by the

formula, C=px dwhere Cis the circumference, pis 3.14, and dis the diameter. For mytent,C= 3.14 x 18 which is 56.52 feet. Subtracting 3 feet for the width of the doorway,leaves us with 53 feet of wall to make. Roundhouses have characteristically low walls,

so in order to stay in proportion, we made our walls 4 feet high. Figuring that the latticewould be opened so that the openings were roughly square, you can determine the correct

length each of the laths in the lattice. To make square openings, all of the laths need tobe at 45 to the horizontal. This means that if the height needs to be 4, the length alongthe ground is 4, and the lath length can be given by Pythagoras equation shown in the

following figure:


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The laths could be cut at 58 as the figure above dictates, however the topmost rivet willbe spaced 3 from the top, which will affect the circumference. In order to compensate

for this, I cut my laths slightly oversized to 6 0.

1.2 Cutting the LathsI cut three 4x8 sheets of 3/16 thick plywood to 6 feet long, then ripped each 1 3/8

wide lath out of the remaining 4 x 6 sheet using a table saw as shown below:

After setting the tent up a few times, I have damaged many of the laths, and when I redothe lattice (hopefully soon), I will use marine grade plywood to avoid these problems

and make the lath more resistant to dampness. This plywood will be more expensive, butit will give me more peace of mind. I suggest that you start with the plywood to saveyourself the expense of having to buy plywood twice.


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1.3 Drilling the LathsHoles are then drilled in the lath at 1-foot intervals starting with a hole 3 from the top.

In order to speed up the drilling, you can stack the laths into tall bundles, and drill the

bundle all at once as seen in the following pictures:

Marking the hole locations with a completed lath.

Drilling the holes. The wood clamps are holding a fence that I am pushing the bundlesonto to keep the holes in the middle of the laths.


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1.4 Assembling the LatticeOnce the laths are cut and drilled, it is time to attach them together. I used pop-rivets formy assembly because they were quick and easy, but bolts, knotted string or rawhidecould be used. I found that a very tight washer was needed to stop the pop-rivet plunger

from pulling through the lath. In my case, 3/16 pop rivets needed 4mm washers. It

takes about 200 pop-rivets to complete a 53 wall section. To assemble the lattice, layseveral laths on the ground parallel with each other. Then lay one lath on top of themleaning in the opposite direction. Make sure that all the laths have the 3 hole spacing atthe top, and the 9 spaced hole at the bottom. Put a pop rivet through the topmost hole in

the top lath, and the first bottom lath, slide a washer onto the rivet from underneath, andpop the rivet. Put a rivet sequentially in the remaining holes on the top lath, then put

another lath on top, and repeat. Looking at the picture below, notice how all of the lathsleaning to the right are behind all of the laths leaning to the left. Without this, the latticewont fold.


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Open the laths to the angle at which they will rest when the tent is assembled, cut one endsquare as shown in the picture below and continue assembling laths from one end to the

other until there are 16 full crosses or Xs at the top, with three single laths that donthave a pairing lath. This will eventually be one half of your wall.

To begin the other half, pair these unpaired laths (single 1-3) with the first few laths of

the second section as if continuing the wall around, but do not rivet these single laths tothe laths of the next half of the wall. I find the wall more convenient to lift and store intwo pieces. These two wall sections will be connected with nuts and bolts during tent

setup and unbolted for takedown. Be careful to continue this wall when making thesecond half, as it is possible to make two wall sections that will not knit together. Careful

comparison of the picture of the real lattice above, and the drawn lattice below it will

reveal that the two are incompatible! The picture has the lath closest to the reader leaningleft, while the drawing has the close lath leaning right. The y have a different

handedness, and no amount of flipping and twisting will make these two sections bolttogether correctly. By the time I learned this, I had wasted around ten laths. Continue

the 2ndhalf of the wall until another 16 full crosses are completed. Cut the far end squarein the same way that the beginning of the 1sthalf wall was cut.

2 Making the Roof Rafters

2.1 Cutting the Top EndThe next parts to be made were the roof beams. I used 1 x 2 x 12 vertical grained fir

boards, but there are lots of light, strong, straight-grained woods that could work. Cuttheir ends at 52 by cutting a block at 38 on a chop saw, then using that as a guide, cutthe rafters with the chop saw set square (0) as can be seen below:


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Cutting them at this angle will allow them to sit flush to the top surface of the roof ring aswill be seen soon.

2.2 Notching the raftersThe rafters need to have a notch on them to sit in the crosses on the top of the lattice.

This notch holds them in place, and keeps them from sliding. With a handsaw, notch therafters about deep, at a 38 angle, 10 from the top point, and 20 from the bottom.The finished rafters should look like the drawing below:

The 20 of rafter after the notch allows the roof canvas to overhang the walls, and adds to

the roundhouse appearance. The roofs of actual roundhouses would overhang the wallsto protect the mud daub of the walls wattle and daub construction from getting wet.

Thirty- five of the 36 rafters need to be finished in this way. The last rafter will intersectthe doorway ridgepole, and will be shorter.

3 The Roof Ring

For ease of measurements, my roof ring has 36 sockets to hold 36 roof beams. Thismeans that each beam is 10 from the next one, which makes for nice, round numbers.

For a smaller diameter tent, fewer rafters could be used. The ring is a sandwichconstruction having a top and bottom of plywood, and an inner core made up of manysmall pieces of cut wood. In the center of the ring is a threaded block of wood ready to

accept the pole that holds up the peak. A cross sectional diagram can be seen in the nextfigure:


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3.1 Cutting Out the PartsThe block to the top- left of the above drawing shows how the angled blocks were cut

from a 2 wide board at an angle of 38 set on the miter saw. These angled blocks arethen glued and nailed (with a nail gun) to two square blocks, one on either side, the same

2 length, and 2 1/8 high. The following is a picture of the 36 angled blocks, and the72 rectangular blocks after they were cut.

The next step is to cut out the top and bottom layers of plywood. First, establish a center

point, and then using a piece of scrap wood with a screw in it as a compass, put a pencil

through holes drilled in the scrap at 28 and 22 from the center, and draw the insideand outside circle of the roof ring. The setup is shown below:


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After the two rings are drawn, draw a line on either side of the scrap/compass, making a

strip 3 wide that passed through the center of the ring. This will hold the threadedblock mentioned earlier. The top and bottom pieces are then cut out using a jigsaw, and

the edges smoothed with a rasp.

3.2 Assembling the RingThe 36 block assemblies are glued and screwed to the bottom ring circle, starting with

the four corners, and the rest were glued and screwed down starting with one quadrant

at a time. These figures show the process:


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Here are all of the blocks in place on the

ring. Some of the inner surfaces of the

blocks where they touch each other neededto be thinned so that all of the blocks could

fit. This could be avoided if the ring wasmade slightly larger in diameter.

The next thing to do is to put a x 2 1/8 piece of wood brace on either side of the 3 strip to which the threaded block could be screwed. I drilled large holes in these bracesto try and keep the weight of the ring down. The finished ring with braces, threaded

block, and top plywood attached is shown in the next picture:

4 The Doorway

One of the classic portions of a roundhouse is the entryway that juts out from the walls.In order to affect this on the tent, an inner doorway had to be tied to the walls, and an

outer doorway attached to the inner doorway. For this, I used a pegged mortise and tenonconstruction to simplify portability and storage. The sides of the inner door are made by


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sandwiching a 2 wide x plywood spacer between two x 3 boards. Thespacer was the same thickness as twice the lattice thickness, and was flush with the inside

of the doorway. This created a 1 deep by wide dado in the uprights into which thelattice can be inserted. These dadoes are shown as grey areas in the drawings. This holds

the lattice in place while setting up the tent. The doorway parts are illustrated in the

following drawings:

The last two parts of the roof/doorway to complete are the two beams that form the apexof the doorway. They involve some special techniques, but are not too hard to


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manufacture. The beam that connects the top of the outer door to the inner doorcontinues into the tent until it intersects the 36th roof rafter coming from the roof ring.

This rafter is cut there to the correct length to fit into a sheet metal socket on the doorwaybeam. The basic idea is shown in the next picture:

The metal bracket is 16 ga. or thinner sheet steel or aluminum, the large holes are there tolighten the steel, and the smaller ones are to screw or rivet the bracket onto the rafter.The bracket should be laid out as in the following diagram:

The beam above the doorway with its metal bracket has the following dimensions:


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The frame as it stands at this point should look like the picture below:

In this picture, you can see the two belly bands that are tied to the inner doorway andencircle the lattice; one is around the way up, and the other is at the very top of thewall. These are necessary to stop the lattice from swelling out from the weight of the

roof. Each band is, in fact, two straps that join at a tightening buckle at the back of thelattice. This helps to cinch the wall tight, and stabilize the roof.

5 The Canvas

5.1 LayoutThe canvas I used for the tent is Sunforger flame retardant, water resistant 12 oz. Canvas.I was willing to spend a little extra on the canvas, in hopes that this would be the last timeI would have to pay for it in many years. There are many ways to lay out canvas to make

a conical roof, but I chose to use the method that had the fewest seams, as I figured thatthe sewing would be both the hardest and most time consuming part of the project, I

thought that I should minimize it. The calculations are probably way too involved fortheir own good, but I finally got to use some high school mathematics for somethinguseful. To see the calculations in their entirety, refer to Appendix 3. First the cone shape

is calculated, then the shape is laid out on flat canvas. The canvas I used was 60 wide,which made the layout relatively easy. The layout is shown in the following drawing:


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It took 6 strips of canvas to complete the layout. Once these sections are sewn together,

lay the canvas over the already set up frame, and check the fit. Clamp the wedge shut,and see how it fits the frame. It should fit well, without being too tight. At this time also,

you can lay a piece of canvas over the doorway, and mark the interface seam between thedoorway roof, and the conical roof. It creates a rather complicated seam with lots offitting, but it can be done. Remember to measure thrice and cut tomorrow. The final roof

shape (before sewing the cone seam) should look like this:


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With the doorway roof sewn on, the entire, monolithic roof, as viewed from above,should look like the following picture (the three newest seams are shown in red):

Once the sewing is completed, the roof should be placed back on the frame, and thealignment of all of the rafter ends should be marked on the outer rim of the canvas. This

will show where grommets should be placed in the canvas to tie the roof onto the frame.

Compared to the roof, the rest of the sewing is dead easy. The wall surrounding thelattice is merely a 54 long, 4 high, hemmed sheet with grommets around the top to tie itto the lattice Xs and some at either end to tie it to the door frame. The walls of thedoorway are two panels 3 wide, and 5 feet high, with pockets sewn at either end through

which the top and bottom entryway beams slide. The cross section looks like thefollowing:

The roundhouse is now pretty much complete. All that needs to be done now, is to set it

up, and live in it for a while.

6 Setup

Setting up the roundhouse can take some time, but if things are done in the right order,

lots of hassle can be averted. The Doorway is assembled first, including the canvaswalls. Insert the tenons though the canvas and the mortises, and then drive the pegs in,


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securing the joints. Then stretch open the two lattice sections, bolt them together, and tiethem into the slots in the inner doorway. The belly bands should be put in place and

snugged up as needed during the whole process. Next, someone on a short ladder shouldhold the roof ring in place while roof rafters are inserted in their correct slots in the ring.

Care should be taken to count the ring slots and the lattice Xs to put the correct rafter in

each slot. Otherwise the ring will twist, and the rafters will bend. Once all the rafters arein, they should be secured into their X, while also hanging the wall canvas, by knotting a

small piece of twine around the wood and through the canvas grommets. Next the roofcanvas goes on from the entryway point over to the other side, to keep it from being

rotated with respect to the frame. Grommets on the outer edges of the roof canvas can beused to tie the roof under the rafter at the end, and to the lattice. The last step is to put ashort, threaded dowel into the threaded hole in the roof ring, and raise the peak. In the

future, the peak will be made with a separate cap that can be raised and lowered byturning the threaded dowel to which it has been attached. A drawing of this mechanism

can be seen here:


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Appendix 1Reconstructed roundhouses

The Large Roundhouse reconstruction at Butser Ancient Farm in Hampshire, U.K.


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The reconstruction at Flag Fen:


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Appendix 2The completed roundhouse


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Appendix 3Roof Math

From the edge of the rafters to the peak of the roof is around 13 feet. If you add 6 for

the canvas to roll under the rafter at the bottom, the canvas layout can start with a circle

with a radius of 13 6. Anyone who has made a cone before could likely tell you that acone is made from a circle with a wedge taken out of it as in the following drawing:

The question becomes, how big is the angle ?? The answer can be found using some

geometry. First, we need to find the diameter of the cone of canvas when its in its finalshape. That is, if you were hovering directly over the roundhouse looking down at it,

how big would the circle look to you? We know that the roof rafters hang over the by20, at an angle of 52 to the vertical. In pursuit of excessive mathematics, the amount ofoverhang can be calculated in the following way:


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If we take the resultant 15 overhang, and add that to the diameter twice (once for eachside) we see that the circle would appear to be 18 + 31 , or around 20 8 in diameter.

The circle above has a diameter of 13 6 x 2 = 27. That means, to make a cone with thecorrect shape, you should cut out a wedge big enough to leave 779 around the outer rim

as shown below:

To find the angle ?, the ratio can be set up using angles of a circle. A circle has 360 allthe way around the perimeter, and for a giver radius r, the circumference c can be written

as c = 2pr. This equation assumes that we care about the total circumference goingaround all 360. What if we want to know what the circumference is? This

corresponds to the circumference described by a rotation of 180 of the total 360. Forany random angle x, the circumference of the wedge can be described by the formula:

Solving for the angle x, we get:

since we know c = 20 8 x p = 779, and we know that r = 13 6 (156) we can solve

the equation and find that x = 286. This means that ? = 360 - 286 = 74


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Appendix 4Materials list

3) sheets 3/8 Marine Grade plywood

1) sheet plywood for roof ring

36) 1x 2x 12 vertical grained fir boards

11) (approximately) 1x 4 wood of your choice (for doorways, doorway rafters, androof ring blocks)

Scrap amounts of plywood for the core of the inner doorway

Scrap amounts of sheet metal for the rafter bracket

120 cotton webbing or rope for the belly bands

twine

65 yards of 60 wide canvas

Optional:material to make a 3 x 6 door

Door hinges, handle and latch.

roundhouse paper

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