Trying to draw Bow-roof gothic arch for my greenhouse

thanks. I will check this out when I go home.

I kind of managed to draw it with your helps. But I am having a design issue. I thought I can have a 6.4m wide greenhouse using 5m radius. According to this drawing, the width of the greenhouse will be around 5m (ridge beams still to be added!!!).

I might change the radius.

baris1.skp (183.3 KB)


Good work! I looks like you don’t need me to draw it for you after all. :wink:

In order to have it be 6.4m wide and still use the 5m-long strips, I think you’re going to end up more like your original circular layout than a gothic arch:

@DaveR I don`t think I could do this without your help. I had the basic but my calculation was wrong. I have created my actual jig according to 5m timber. I attached a pen at the end of the timber and draw a circle. That is why I just wanted to dublicate that setup on sketchup.

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@jimhami42 Yes, that is the problem. I don`t really want a circular structure. I think I will shorten the width so that it will look more like gothic arch.

If you have a 1m upright, which you appear to have, you can do a very nice Gothic arch with a 5m Radius on a 5m beam.
If you look here at my rough sketch, the actual curve is less than 5m but gives you 4.6 X 5.6 or there abouts. If you don’t want it so tall, reduce the upstand.

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@Box 4.6m is too narrow for what I need. I am allowed to build a greenhouse upto 465 square meters. My original plan was 72 meters by 6.4 meters.

Now, I think I will go for 76.8 meters by 6 meters. I hope this wont cause any issues.

Can you please share that drawing.

Sorry I misread your dimensions.
I didn’t save it as threw it together as I was having a coffee and now I am on my phone.

I understand why you’d like a 1m vertical part at the base - a green house is likely to have benches of at least plants growing near the side walls so having the wall leaning in too soon seems impracticable.
Since you have to bend the 5m timbers [consistently] and then assemble then into an arc to form the sides of the ‘gothic-arch’, I assume you’ll use a ‘jig’ and clamps etc while the glue sets and things are screwed together etc…
This means the curve need not be a single arc.
You could consider with two arcs or an arc+straight, which then meet at a reduced height and even a greater width, whilst keeping a similar form ? The whole side including the 1m could be made in one piece ??

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@TIG It will be very hard for me to create that jig. I have already created a basic jig which has a radius of 5m.
Also, I am not sure how strong those ones will be.

Just ideas…

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Did you really want 72 meters long?

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Here’s how I ‘drew’ it assuming the fixed jig radius of 5m,
I approximated the 12 segments’ length by dividing 5m long timber into 12 parts.
I then rotate-copied the adjusted first segment so I end up with 12 segments.
The width is then ~4589mm and the height ignoring any 1m ‘plinth’ wall is ~4205mm
The first segment is not quite vertical
The sweep of the segments is 57.24° not 60°.
If a 1m plinth is used the height is ~5.2m.
If the 1m vertical is not used, then the first 1m rise of the arch only leans in by ~105mm so it’s hardly intrusive…

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@Box That looks really artistic but not practical in my case. I can not have central support. What is the length of the arch? Do you not think it will support itself without the center blocks?

I’m no mechanical engineer, but logic tells me over 72 meters you need some support.
The arc works for your sizes, the rest is artistic license.
It’s only one support every 10m.

I worked backwards … a 5m radius will trace out a 5m length at 180/PI degrees = 57.29578 degrees. Using the Arc tool, I created a 57.29578 degree arc from a 5m distance center point using 48 segments.

I essentially arrived with the same results as you did with some extra work :wink:

That’s basically how I drew it yesterday, too. Maybe I’m the only one that can see my post, though. :wink:

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One of the neat things about using a gothic arch for this project is that it’s naturally supportive no matter how long the greenhouse is:

Fixing one end of the arc to the ground and the other to the ridge beam forms a natural parabola which equally distributes the load along the beam. The sides hold the ridge beam all along the length so that no other supports are needed. Note that the example above deviated from the true arch and needs cross braces along the midpoints of the arches.

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I think what it boils down to is, if you have a 72 meter greenhouse design, you need a structural engineer to design it. If you are bending bits of wood and trying to produce drawing to suit then you are asking for trouble.
Is this a commercial undertaking? Are we helping you design hemp houses.?