Or how not to build a catenary curve chicken coop.
Back in 2007 I rescued 7 baby chicks from a cull of feral chickens in a local park. I eventually built them a large A-frame coop-and-run, but as they were mostly free-range in our back yard (and more often than not in the front yard), even back then I had plans for a smaller, more easily movable "night-coop" to sit inside a proper run.
The coop needed to be dog-proof, for when it was used in the vege garden, and dark enough so the chooks would not wake too early and disturb the neighbours. It only needed to be big enough for about 8-10 chooks to sleep in, as the coop would be attached to a large run.
As a fan of curved architecture, I chose to build based on a catenary curve. Here's how I attempted it. You will want to learn from my mistakes...
I had thought I'd come up with a new concept, what with finding nothing on the Web, but after starting construction I found a very similar design. Typical! This appears to be the entire living quarters though, whereas mine is only the bedroom.
This one deserves mention also.
Step 1: Establish a Catenary Curve
A catenary curve is the shape made by a chain hanging from two points. This is distinct from a parabola. Freely-formed honeycomb takes a catenary curve apparently. As I wanted a coop 1m wide* with a curve of 2.4m**, I figured there would be an online equation for a catenary curve such that I could calculate the coop height. Well there is***, but I can't make head or tail of it. There is a simple version I'm sure, but I can't find it!
Well, duh. After much web surfing and learning more about curves than I thought possible, and after actually building most of the coop, I came up with the brilliant idea of tracing the shape of a 2.4m length of chain nailed to ply. By measuring 400mm down the centre-line from the base, I could then square-off the curve with a couple of nails/screws to allow for a wider shape.
If I was to do this again, I'd use this technique to cut two full ends (using the first end as a template for the other panel) and bend the ply over them (much like building a boat hull, but see what happened in the next step...).
*(to fit on my garden beds)
**(NZ ply is 1.2 x 2.4m; equivalent to a sheet of 4 x 8ft)
*** http://en.wikipedia.org/wiki/Catenary and http://curvebank.calstatela.edu/catenary/catenary.htm
Step 2: Build the Base Frame and Bend the Ply
After building a 0.9m x 1.15m base frame from 50mm x 75mm (2" x 3") timber (to fit inside the garden beds and allow for a 25mm ply overhang at each end), I began the task of bending a full sheet of 6mm 3-ply cross-ways into the desired shape. A wood-steamer would have helped, but lacking that I used rachet ties and hot water... It didn't work as you can see from the second picture. 3-ply bends better down its long axis as two of the sheets have their grain running that way - I was trying to bend across their grain.
After cutting the damaged ends square, I now had two pieces 1.2m x 1.15m with the grain in the 1.15m direction. What I should have done is cut the full sheet in half to begin with.
[Hindsight: I wonder if kerfing across the width through one or two layers of ply in several places either side of the centre line would have helped?
Step 3: Fit Ply to Base and Rafter
After screwing the two sides to the base board (with the ply grain running parallel to the floor), I joined the tops with screws into a length of 50mm x 50mm timber (2" x 2"). This timber is 12mm shorter at each end than the walls to allow for the thickness of the end walls. This formed more of a gothic arch than the catenary curve I was hoping for.
The next task was to add a 50x50mm cross-member to one end, 400mm from the floor. I didn't take a pic of this, but you can see in the next step how it swells out the shape. If I had cut the end walls from a template as described in Step 1, I would not have needed this as the end wall would control the curve: the nesting shelf could then be simply screwed to the end wall.
Step 4: Fit the First End (small-door)
My apologies if this step is a little messy: I didn't take photos until after the step was finished and I had a part sheet of old 10mm 7-ply so, wrongly, used that for the first end. It was slightly warped and quite splintery, but I can be a bit "cheap" frugal and was hoping I could build the entire coop with materials to hand. If I did this again, I'd use one whole piece of good ply as I did for the other end. If you like, you can skip to Step 6 to see how it should be done!
Because I had already built the base frame, the few mm's I lost by breaking the ply meant that I couldn't have the end wall ply on the outside of the frame - hence the little cleats in the first picture. Hindsight says "take a few minutes to knock the frame apart, shorten it, and re-nail it". [More hindsight some months later: I could have just done away with the 10mm overhang at each end as the corrugated roof protects them anyway - damn! Oh well.]
I don't have a photo of creating the curve for the top part of the wall, but I did it like this:
1 Stand the coop, now splayed by the 2x2, on its end onto the ply and mark inside along the base and partly up both sides
2 Insert a sheet of corrugated cardboard (an opened-out box), between the coop and the ply, and mark the inside of the best curve (cheapo ply doesn't always bend evenly)
2 Cut out along the line on the cardboard, remove the coop and use the cardboard template to draw both wall curves onto the ply
3 Cut out the ply with the jigsaw
As I had several ply pieces for this wall, I now fitted them. the bottom pieces were easy enough, but the top (curved) piece required a bit of manipulation to get inside the side wall ply. All the pieces sat against the cleats, the end bar and the ridge beam, into which I nailed them with 30mm flat-headed nails. The top door (for the nest) is 400mm high and 630mm wide. The bottom door is 400mm square.
To fix the side wall ply to the thicker end wall ply I used the technique shown in Step 8.
Step 5: Cut the End Doors and Hinge Them - Nest End
We need a door in this wall to access the nests - if you decide to do this after reading Step 9. Using your hand as a scribe*, draw a curved line about 100 - 125mm (4 - 5") inside the curved sides and a straight line about 50 - 75mm (2 - 3") above the bottom of the upper end wall.
Use the jigsaw to plunge cut** into the ply on one line a short distance from the corner where two lines meet. Once you've made a hole, cut back toward the corner and repeat the process for the adjoining line. Screw a small piece of ply onto the corner to stop it falling through later.
Cut the rest of both lines.
Plunge cut into the third line in the same way, cut back to the nearest corner, and screw on another support piece.
Cut almost to the final corner then screw a third support into the door about 3/4 way to the final corner. Finish the cut and remove the door. At this point you've made a mistake that will soon become obvious.
Fit two hinges to the bottom of the door (on the straight line). I kept the support pieces on while I did this. Take off the supports and realise that the geometry of the bottom corners won't allow the door to fully open! To fix this I had to round off the corners with the jigsaw and glue the little triangle pieces this made back into their corners. If I had made rounded corners in the beginning, I could have done one complete cut from the peak corner right down one curve, along the bottom and back up the other curve, using support pieces as I went. Hindsight: wonderful thing. See the Step 6 for how I did the other end.
The bottom door was an easy fit with the hinges also on the bottom. In hindsight, I'd have hinged it on one side so bedding material didn't keep blocking closure.
* a.k.a. marking gauge. To use your hand, lay your little finger along the outside of the roof and adjust your finger position on the pencil until you can reach where the line goes with the tip of the pencil - now just run your hand along the curve.
Step 6: Cut and Fit the Big-door End
This is where I splashed out and bought a sheet of cheap 12mm untreated ply, which I should have done from the start.
If you cut both end walls from a template as described in Step 1, the next two marking tasks would be unecessary.
Once you're happy with the small-door end, place that end on the ply and pencil-mark around the coop. Due to my earlier mistake, this wall was shorter than it would have been, so that it would sit on top of the base rather than outside it.
Using a scrap piece of the roof ply (6mm thick in my case), mark a line inside the original line and cross out the original so you don't confuse them.
Cut along both lines so the cuts meet at the peak.
Nail a cleat right along the frame, but 12mm back from the edge, for the end wall to sit against (same as the other end).
Tip the coop on its end and place the new wall on top. At this point I almost had a hissy fit as it was too short, no matter whether I lined up the top or the bottom. After some deep breaths, I realised that the wall would fit fine once the roof was bulged out a bit. To fit the new wall into the curve of the roof I laid the coop down again, pushed on the peak to bow the roof out, and tapped the wall into place with a hammer. At this point it was resting on the bottom cleat and the ridge pole.
Nail the wall onto the bottom cleat and the ridge pole. You could also do Step 8 at this point if you like, but I was still guessing my way through so did that later.
Step 7: Mark and Cut the Big-door-end Doors
Start by marking two lines inside the roof line by using a scrap piece of ply about 100mm wide, or what ever looks pleasing. Draw a straight line parallel with the bottom - in my case this line was level with the top of the cleat inside the wall. These lines are for the big door. For me this made a door 800mm high and 730mm wide: big enough for even me to get into!
Next you need to round off the corners: this not only looks nicer, but is a lesson we learned from the upper door on the other end. I started by using my drill-bit container as a template, but decided the curve was too tight so used an electric fence wire reel instead. You could use paint cans, tin cans, frisbees, whatever. Place the template so its curve just touches the lines either side of the corner then draw around it. Leave it at that for now.
Designing and drawing the little pop-hole door is next. Start by marking a horizontal line about 100mm above the bottom of the big door and a vertical line down the centre of the wall. Decide how high and wide you want the door to be - in my case it was 300mm by 270mm. Mark these dimensions on the horizontal and vertical lines. Finally, use the marks on the horizontal line to draw two lines parallel to the centre line.
Get a stick or other straight-edged item that is longer that the pop-hole is wide. Place one end on one side of the pop-hole and mark where the other side crosses your stick. Now place the unmarked end on the peak mark and angle the stick until the stick's mark meets one side of the pop-hole - mark this spot. Do the same on the other side.
Keeping the stick mark and one side mark together, place your pencil at the unmarked end of the stick, and swing the stick so your pencil draws an arc from the peak mark to the opposite side of the pop-hole. Repeat this for the other side.
Use a small round thing (in my case the drill-bit container) as a template to round off the bottom corners. Plunge-cut the pop-hole door out, remembering to back-cut to the peak first, then turn the saw around and cut right around the line until you reach the peak again. If the coop had been catenary instead of gothic, I'd have rounded off the peak also. [Hindsight: could have done that anyway, I suppose...].
Now cut out the big door, remembering to screw in cleats as you pass the corners and another one just behind the saw just before you reach the end of the cut.
Great! Now put hinges on the doors. I was a bit cheap frugal and used hinges that were not rust-proof, so have had to replace them since - bad economics! When I replaced the big door hinges, I side-mounted them as bedding litter kept interfering with closing the door - the only problem with that is that the corrugated roof means I can't open the door fully! But it opens far enough.
If, like me, your hinge screws are too long, sand or file them flush.
Step 8: Screw/nail Roof to Walls
You may want to do this step before cutting out the doors, but it didn't seem to matter in my case. I did it between cutting out the doors and attaching their hinges.
Because the end walls sit about 10-15mm inside the roof edge (the "wall inset"), you'll need to mark where the inside of the 12mm ply sits, so you know where to put your nails. Here's how I did it:
1 Take a scrap piece of ply and draw a line parallel with one edge 12mm (or however thick your ply is) in from that edge.
2 Cut a notch out that is slightly wider than the roof thickness and longer than the wall inset and the wall thickness combined (in my case greater than 15mm + 12mm = 27mm). This will form a "leg" which will run along the outer side of the ply.
3 Cut along the 12mm line so that the leg is that much shorter than the rest of the ply.
4 Use this template to mark where the inside of the wall is. By putting your pencil on the 12mm line, you could also mark where the outside of the wall is. [Hindsight: if your leg was only half the thickness of the wall (in my case this would be 6mm), the line you draw would be the midpoint of the wall's thickness - which is what you're really after.]
Now drill several pilot holes for your screws along the midpoint of the wall's thickness - mine were 100-150mm apart. The holes are only to guide the screws or nails, and help prevent splitting so they should go all the way in, but not be wider than the screw or nail.
Put in the screws. I started by using screws (drywall/Gib screws because I had them on hand, they're skinny, and hold well) but ran out so used decking nails instead, which have held fine.
The last stage is to drill and screw/nail the bottom of the wall to the cleat.
Do all this for the other end too.
Step 9: Build Nest Boxes
Forget it: this will take too long to explain, was more complex than necessary (but looked cool!), and I ripped the nests out later as I got some rescued battery farm hens about the time I started using the coop and they ended up laying on the floor until I gave them some outside options. They also started sleeping and pooping in the nests. Part of the problem was access, I think: I should have had a rail just in front of the holes for the chooks to stand on, or have done away with the holes entirely. [Hmmm, might re-look at this...]
If you really want inside nest boxes, a better option would be a simple unit with a couple of nests (rather than the three I had). Here's a good example. This is not divided, but that's easy enough to add if you want. The picture below shows the nests I'd made for the original A-frame coop; the lid stopped them pooping in the nests.
Step 10: Fit Perches
Again, there's a lot of explanation for something I'd do differently next time, so I won't go into detail. Perches should really be removable for cleaning and mite control. It also makes it easier to clean the coop, or to use it as a dog house (or pigs!)
What I recommend is to use notched or cleated runners, as in the attached picture, with, say, three notches wide enough for 50x50mm perches. This can easily be screwed to either side of the coop just where the roof starts curving inward. My perches are at different heights as I was thinking about the chickens' pecking order: the higher up the order, the higher they want to be. You could achieve the same result by angling the runners (as in the attached picture from www.backyardchickens.com).
So this bloke wants chickens and builds a coop with enough perches for ten hens. He goes to buy the chickens but is told he can only buy them in batches of twelve. He agreed, but would have to add two smaller perches above the main one for the extra two chickens to perch on. How many chickens did he pay for straight away?*
*Ten: the other two were on higher perches** :]
Step 11: Make and Fit Door Catches
I made my own, but because I used water-based wood glue to hold them together, they haven't been as successful as I'd hoped. Here's how to make them, with notes on what to do differently.
Use the large template item used to make the round corners of the big door, and draw tail-less-fish shapes (ellipses) that are about 100mm long on the 12mm ply. If you know how to draw unpointed ellipses, you could do that, or even make them an egg shape. Cut them out with the jigsaw and sand them smooth. You will need two for each door.
About a quarter of the way in from one end drill a hole that will snugly fit dowel axles. I made my holes about a third of the way in and used 10mm dowel, but this distance made fitting the catches difficult.
Cut dowels that are slightly longer than the thickness of two ellipses and the wall (in my case 12+12+12+a bit = 40mm). Glue one end of each dowel onto an ellipse and leave it to set.
Take an unglued ellipse and hold it to the wall so that the hole is directly above the peak of the door, and above it by a fraction more than the shortest distance that will allow the catch to swing free of the door. Use a marker that will fit inside the hole to mark the location, and drill through the wall at this point.
Take a glued ellipse, poke the axle through the hole in the wall, and glue on the unglued ellipse. Be careful not to get glue on the door. The two ellipses should be slightly out of alignment with each other so that when the outer one is open, the inner one still provides a backstop for the door. When the glue has dried, sand both ends of the axle flush with the ellipses.
[Hindsight: you could also use just one ellipse per door, use a nut and bolt as the axle, and screw on a permanent cleat as a backstop].
Step 12: Paint the Coop
Simple enough. Sand off any rough spots, fill any major blemishes with a two-part epoxy filler, and paint. I used green exterior house paint to help make the coop less visually obvious and because I had a lot left over from painting our house.
I did not use a sealer or undercoat, but the house paint has stuck well even years later. I gave the coop two coats inside and out - this helps protect against rot (the timber is not treated), and to seal any little cracks that mites and lice might hide in.
At this point you're done, unless you want to add a overhanging roof and a floor. If you do, read on.
Step 13: Add Corrugated Overhang Roof
I wasn't convinced that the coop would be weatherproof enough as it was so decided to add a better roof.
I bought two cheap 1.8m sheets of corrugated plastic with a view to having them meet at the top and be covered by a ridge of galvanised steel. Unfortunately, that did not really work due to the corrugations, so I went with Plan B.
Lay one sheet over the coop so that the middle corrugation is face-down on the peak. Measure the overhang, divide it in two, and adjust the sheet's position so there is equal overhang both ends. Put screws through the tops of the second corrugations on both sides and both ends (i.e. four screws), to hold the first sheet in place. It is best to drill pilot holes first; through the plastic and into the edge of the end walls in my case, but you could probably drill straight into the curved ply if your screws are short enough.
Cut the second sheet in half lengthwise. The plastic I'd bought turned out to be very brittle and was difficult to cut without random fractures: that's what you get for buying cheap stuff. I eventually carefully used a pair of secateurs instead of the jigsaw.
Fit the half sheets underneath the first sheet by one corrugation and screw them in place.
Paint the plastic to blend it with the coop and protect it from the sun - not all plastic is sun-proof, especially the cheap frugal stuff.
Step 14: Add a Floor
I didn't do this originally as I had plans to scrape the poo out from the ground at regular intervals. Unfortunately the poo got quite wet, what with being on soggy ground, so I added the floor. A floor also keeps the draughts out and the chickens warmer.
The floor is wider than the big door's width, so I cut the floor in half lengthwise. This makes removing it for cleaning (or for summer) a lot easier. Because my floor was made from the same 12mm ply as the end walls, I haven't had to use joists to support it, but you may have to. [Some months later: nope, just checked it and it is sagging a bit under the weight of the bedding and poop. I'll have to add a joist to support it]
Step 15: Now Use It!
I started using the coop in the vege garden where the remaining three bantams we had at the time were clearing one of the beds. A neighbour gave us a shaver-cross hen in barter for rooster "processing" skills. Once the back yard run was fenced off, we shifted the coop to there and later added four Brown Shavers rescued from that despicable torture known as a battery farm - they looked terrible, but have recovered perfectly as you can see.
I built a feeder to stop the sparrows and local diamond dove flocks from stealing all the feed. A NZ company makes these commercially (www.grandpasfeeders.co.nz).
The neighbours have not complained about early morning noise, so I guess the coop is working!