Introduction: 3m Geodesic Dome Greenhouse
At home, we have a roughly 3m wide, semi-circular piece of land. We also want a small greenhouse. Putting one and one together, it made sense to make a small greenhouse on the small piece of land. It is not perfect for a greenhouse (only receiving 4-5 hours of full daylight a day), but it is the best we have.
The shape of the ground makes an ordinary greenhouse difficult. Also, I have a love for Geodesic domes. Since the piece of land is already round, it made sense to make a Geodesic dome. I love domes because they are ridiculously strong and efficient. All struts are only every pushed or pulled on. No bending load ever goes through a strut. Also, the structure of a geodesic dome looks very complicated, but is actually easier to build, because it is massively over-defined. You only need to cut the struts to length and remember the pattern to completely build it. No tape measure is ever needed during construction.
Step 1: Design
First some theory and material choices. A geodesic dome is not difficult to make, but a few things need to be understood before making one.
Lets start with the foundation. The dome needs to be anchored to the ground in a proper way. It is easy to skimp out on this part, since you will not see it later, but a strong foundation is what makes something last. How you do it depends on how long you want your greenhouse to last. Here in the Netherlands, concrete gravel tiles are easily obtainable for free. They were popular once, but not any more, and when people get them out of their garden, you can usually pick them up for free. This is a win-win, you get free tiles, and they don't have to take their tiles anywhere (weighing 30kg each).
The frame is the part you will see, so aside from just strength, aesthetics may also be a consideration. The beauty of the dome is its strength, so you will quickly pick something too strong. Bear in mind that what you pick will need to be: A. easy to work with, and B. cheap. You are going to need a lot of it. My choice was simple pine wood, 28mm by 44mm. It costs around 1 Euro per meter and is more than strong enough.
The covering for the greenhouse is the last material being discussed here. There are 3 paths you can take here: Glass, polycarbonate and foil. In decreasing order, they last, centuries, decades and years. I would love to pick glass, but it is also the most expensive. Polycarbonate you pick if you want to make a well insulated greenhouse, but the cheapest by far is the foil. It is easy to work with and is relatively cheap. When picking foil, do pick greenhouse foil. It is made to withstand UV radiation.
Two compromises need to be made in the construction. The first is the bottom spacer. The radius of the dome is roughly 1,5m. This would also have been the height. I am 1,95m and I want to be able to stand in the greenhouse. With no other solutions, a 0,6m spaces is needed at the bottom. This raises the start of the dome, but is also a structural weakness. The dome itself is very rigid, but the spaces, consisting mostly of squares, is kinda wobbly.
The second compromise is the door. In an ideal situation, there are no interruptions in the frame of the dome. The door is a giant gaping hole. Extra wood was added around this area, but even then, it is still the weakest point.
The corner block are the most varied part of the dome. Everyone has a different system, and all of the different systems have their own drawbacks. My choice as 2 1cm thick plywood disks, one 15cm and one 8cm. When these are stacked, they give a roughly 17 degree angle. The 2V dome that is being built here needs either 15.86 degrees or 18 degrees, so it is perfect. The struts are attached from the back with screws.
Making a window in a geodesic dome is fairly straight forward. Make a triangular frame that will fit in one the the domes triangles and add hinges.
The lengths of all things (tiles, struts, spacer) are dependent on each other. I will provide means of calculating all lengths, but because of the tiles, I cannot provide a simple formula to calculate everything. It will take some additional calculations based on the materials you will have available. For the stone and wooden ring, go to:
To calculate the sizes.
The stone ring requires the most thinking, because it is different for everyone. You will need to make a ring, the size of you plot. The size of this ring will largely determine the size of the dome. Choose a >14 polygon, and for 'a', enter the length of the tiles you are using. Now keep modifying n until you reach a diameter that will suit you. Remember that you also need to add the thickness of your tiles to the radius to get your outside radius. Also remember 'r' and 'R', these will need to overlap with 'r' and 'R' for the wooden ring.
The wooden ring is at the base. It will have 10 elements, always, so the length is easier to calculate. insert n=10 and keep modifying a until you have the right radius. The values that need to match are 'r' and 'R'. These are the minimum and maximum radius. The radii of the stone ring need to fit within the radii of the wooden ring, where you need to be closer to the 'R' side than the 'r' side.
In my case: I have tiles with a length of 0.6m. If I take 15 of those tiles, r=1.41m and R=1.44m. My struts need to fit within that, so I picked 0.9m. This gives: r=1.38m and R=1.46m. These fit within each other, and are closer to R and to r.
Calculating the strut length is easier.
Here you will find calculators. The one that is needed is the "2V/L2 Icosahedron Dome". You will have to modify the diameter of the dome in the calculator until the B lath length is equal to the inside length of the wooden ring. Now write down the A length and B length, so you will have it available later on. In my case, I had a diameter of 2.915m, which gave me a strut length of 0.9m. This gives me strut lengths of A=0.795m and B=0.900m. This is inside length, connector to connector.
Step 2: Materials
These are roughly all the materials you will need to make a 3m wide geodesic dome. If you want to make a bigger one, you will have to recalculate the material you need.
- Concrete tiles 40x60x5cm (15x)
- filling sand (20kg)
- 28x44 wood (24x3,5m)
- 10x30 slats (20x2.1m)
- hinges(2x for door, 2x for window)
- greenhouse foil (at least 4mx6,5m)
- humidity barrier (like roofing material)
- Concrete dowels
- spirit level
- hammer drill
- cordless drill
- (nail gun)
Step 3: A Strong Foundation
The first step of making a greenhouse that will last is a strong foundation. I decided that a border of concrete tiles dug into the ground would make a sound foundation. It is quite a bit of work to get the tiles in the ground (weighing 30kg and having to go 40cm deep), but it will be worth it in the long run. For this foundation I will use 40x60x5cm concrete tiles. They are a standard size here in the Netherlands and they are easy to come by. If you are not able to find the same tiles, comparable tiles will also work just as well.
To make a neat circle, I made a special measuring tool. A small stake was stuck into the ground. A piece of timber with the correct length was attached to the stake in such a way that it can swivel. Every tile will be placed at the end of the timber.
For each tile sits in a hole 40cm deep and 60cm wide. If you dig the hole a bit deeper, you can then fill it with leveling sand, which provides a better foundation than the clay we live on. When the tile is in place, check whether it is level in every direction and compared to the piece of timber of the tool. When you are satisfied that the tile is in the correct place, fill the space surrounding the tile back up with soil.
Repeat this step, in my case, 15 times to make a full circle.
Step 4: The First Layer
The first layer of wood needs to connect to the concrete tiles.
The first thing is to cut the wood of the bottom layer to size. The angle of the cut needs to be 18 degrees on each side (10 elements, 36 degrees per element, 2 sides), but the length depends on the size of dome you are building. In my case, the elements are 900mm measured from the inside. It might be wise to test fit the elements before painting.
Paint the bottom of each of the 10 elements with a primer. Do it properly, it will be unreachable once it is mounted and water might get to it. Allow the primer to dry and while you are waiting, proceed to the next step.
A humidity barrier needs to be mounted between the concrete and the wood. Concrete absorbs water, and if no barrier was placed, the wood would rot away. I used bitumen roofing material, because we had a spare piece from making a shed, but any sturdy and watertight material should work. Cut it in 900mm long, 100mm wide strips, 10 in total.
When the paint has dried, It is time to mount the elements. With my set-up, I had 2 overlaps per element on the concrete. Use a hammerdrill to drill holes the size your dowels require. Place the layer of humidity barrier on the concrete where you want the element to be, place the wooden element on top and start drilling a hole through the sandwich. The holes should be in the centre of the concrete tile, else the tile will crack. When The hole is deep enough, insert a dowel and use a hammer to secure it in place.
If you did well, you now have a nice wooden ring mounted on your concrete ring.
Step 5: The Second Layer
Because the dome is only 1,5m (5ft) in diameter, it is not tall enough to stand in . To remedy this issue, A 0,5m riser is added to the bottom. This will make the top of the dome 2m, tall enough to stand in (even for me).
10 pieces of wood (risers) were cut at the same length. These pieces of wood are connected to the bottom ring with with corner connectors. Make sure the risers are perpendicular to the ground. An additional screw is used to properly anchor the risers to the bottom ring. Pre-drilling may be necessary depending on the screw used.
A second ring of wood, 9 elements (the door is left out) needs to be cut. These pieces of wood are the same as the bottom ring. The top ring is secured to the risers with long screws. The front element is left out, the door will be placed there later.
Step 6: Adding the Dome
Now it is time to add the dome. This step takes a bit of explanation, and some steps may be under-explained because this is not really an exact instructable. Some things need to be done depending on your own situation (like my door frame).
The most important part of a geodesic dome is the corner connector. I tried to find something as simple as possible to make a good corner connector. I ended up with 2 plywood (1cm thick) disks, 1 of 15cm and 1 of 8cm. When stacked, these discs give an angle of about 17 degrees, perfect for a 2V dome. The struts will be connected with screws from the back, 2 per side per strut.
To make the corner connectors, I found a bowl and a cup that gave me a roughly correct diameter. Using a pencil to trace the edges of the discs. Then, using a jigsaw, cut out all the discs. Finally, use a small screw to connect the small disc to the large disc, roughly in the middle. To make this dome, 25 connectors are needed. (Side note, a 2V dome actually needs 26 connectors, but the connector at the front door is not used).
The struts are up next. They need to be cut to length. The 2 rings are actually the long struts, and are 900mm. This will be the reference for the struts. 2 types are needed: The short type (type A) and the long type (type B). With a B strut length of 900mm, the A struts need to be 796mm long. This length is from centre to centre. The connector takes an additional 20mm from each side of the strut. To compensate for this, the A strut needs to be cut to 756mm and the B strut needs to be 860mm long. You will need 28 A struts and 21 B struts. (this is with the elements from the door left out).
Building it up
I have a schematic of the pattern, and a modified picture showing how this relates to the real greenhouse. Now comes the beauty, if you follow, this pattern, the dome basically builds itself. Don't worry about millimetres, it doesn't matter. You don't really have to measure while building, just eyeball it to make sure all struts are somewhat aligned.
The struts for the door (2 A elements and 4 B elements)are left out. The will be filled in later to make the door frame.
Frame for the door
The door is filled in next. I have no exact guide for this. The main thing when adding struts to the dome is this:
Whatever you do, try to make triangles. This is what gives the dome its strength. Around the door additional bracing was added to compensate the weakness caused by the door. Then a frame was built that will hold the door.
At this point the dome is at final strength. If you feel confident about your work, you can test the strength of the dome. I am 75kg, and my frame hardly budged when I hang from it. Funny thing is, all struts are only held in place with 1 screw yet, not 2. This is how strong these domes are.
Step 7: A Nice Door
Next step is to make a door that will neatly fit the frame. How this door will look depends on how you reinforced the door in your frame. Only important thing here is to also include one or two triangles in your door frame to give it strength.
First start off by making a square frame for the door that neatly fits in the dome. Mount it in the dome with hinges and check clearances. When you are satisfied with your door clearance, measure and make a diagonal strut for in the door frame. Then, make a frame to fill the bottom portion of the door. Finally, mount the latch to the door frame and test it.
Step 8: Windows That Open
The simplest way to add a window to a geodesic dome is to make a triangular frame that will fit within a piece of the dome. The easiest place to pick is one of the 5 triangles connecting to the crown (top 5 triangles). These are all type B struts (900mm) and has 3 60 degree angles.
Measure the inside of the struts where you want to place your window. Subtract 1cm (1/2") from this length to give the frame some clearance. Also subtract the width of your timber from this length to allow for overlap. Then cut 3 pieces of wood at a 30 degree angle at the required length. Then fasten all 3 pieces together to make a triangular frame. If you did well, the frame should neatly fit the hole.
Put 2 hinges on one side of the frame. Take the window frame to the hole you want to place it in and use a pencil to mark where the hinges will need to be. Then take the hinge pin out and mount the 2 loose sides of the hinges to the frame. At this point you will notice that the window will not actually open. The corners of the window frame collide with the struts of the dome.
Take the window frame out and at both corners on the hinge side, use a saw to cut the sides of the window frame, at a roughly 30 degree angle. Fit the frame again and see where it collides and take wood of the frame where necessary. When you are statisfied that the window frame is clear of the struts, put it in place.
Step 9: Preserving the Frame
There is not that much to this step. Sand the corners of the frame (to prevent them from puncturing the foil), sand the frame is you want to do it properly, then paint the frame with the paint of your choice. In my case, I used a transparent chestnut brown paint. Paint 2 coat, and let it dry. I used around 1,5 litres of paint for my frame.
Please do bear in mind that painting this takes around 10 hours, it is not large, but it is all beams and has a lot of surface area.
Step 10: Wraping the Frame
It's time to wrap the greenhouse in foil. Now not any clear foil works well. It is best to buy special greenhouse foil. Greenhouse foil as UV stabilizers in it, meaning that it will endure sunlight. Other foils without this stabilizer will quickly yellow or damage due to sunlight.
Initially I bought 2,5m by 6,5m, thinking it would be enough. I did some maths in my head, and immediately realized that that was way too little. I then bought another piece of 2,5m by 6,5m. If you buy 4m by 6,5m, it should be enough to cover the dome.
For covering, follow a few simple rules.
- Always start at the bottom;
- Tension the foil one square or triangle at a time;
- Overlap from top to bottom to make the water flow off;
- Don't mount edges of the foil until everything is in place. Else overlapping will be impossible;
- Try to fold the foil at the struts, rather than cutting. Every cut is a potential leak.
Use staples to temporarily mount the foil to the struts of the dome.
Don't staple down the window foil yet. If it is mounted here, there will be no overlap with the frame and it would leak. In the next step, slats will be mounted make the window frame overlap with the dome frame.
Step 11: Finishing the Greenhouse
The last step is making the dome more water resistant. This is done by:
- Taping the edges.
- mounting slats over all vertical edges.
All of the slats need the same coat of paint the dome had, maybe even better. The slats will be in direct contact with the weather outside. Painting itself is pretty straight forward, just keep in mind that painting 20x 2.1 meter slats will take hours. Two coats should be enough.
Cut one slat into two pieces that will fit on the edge of the window. Try to the slats sticking out as much as possible. Then, wrap the piece of foil for the window around the slats and staple it to the bottom and side of the window frame.
Take a roll of clear tape and tape all the edges of the greenhouse. The staples will have left small holes, that allow water into the greenhouse. By taping them over, water will have a hard time getting in. The tiny amount that does make it through, will not cause havoc.
Last step is to mount the slats over all vertical (or not horizontal) edges. Count the number of edges (both long, short and the spacer) that are steep enough so it will not catch water, and cut the slats to the same length as the struts. Paint the edges after cutting, so the wood is completely sealed. Then, using either a nailgun, hammer and nails or screw, mount the slats to the struts.
After the first rain came, I quickly found that the roof over the door had a too shallow angle. Water pooled in the foil. To remedy this, another strut was mounted under the middle of the roof over the door. This prevents the foil from sagging and stops water from pooling there.
Step 12: Whats Next
This dome was made for some hydroponics experiments I had planned. Last year Hydroponics caught my attention, and ever since I have been working on it. I have made a first revision of a Arduino Mega 2560 based hydroponics controller (photo), which I will probably not share because I think it is too complicated and too expensive to make. I will try to make a smaller, Arduino Uno based controller that is in the price range a hydroponics controller should be in.
Now for the sad part, I will not be using this greenhouse myself. I am moving, and I can't take this greenhouse with me. I move to an apartment with a nice big balcony, so I will be doing a smaller version of my hydroponics experiments there. My parents will use this greenhouse, so maybe, if they do something nice with it, an update will come showing you how it is being used.
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