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Geodesic Dome Notes & Calculator

written by Rene K. Mueller, Copyright (c) 2005, 2006, 2007, last updated Sun, September 22, 2013

Real Life Application

I considered the geodesic dome for doing a temporary building or habitat. Using a set of struts, build by wooden roof laths (very cheap and easy to get here in Switzerland), and building a 5-6m diameter dome for myself to live in it. I merely doing the skeleton of the dome (no faces), and put then a cover over it (shape not yet determined).

Options

Following options for a shelter are considered for me, I target diameter from 6m to 8m, for now I focused only on the Icosahedron based domes:


2V 4/8 Icosahedron Dome
2V 4/8 Dome with

  • llath 3m long lath (A+B)
  • 5.62m diameter
  • 35 laths

For my personal taste it's too edgy, and won't really consider it.


3V 4/9 Icosahedron Dome
3V 4/9 Dome with

  • 5.39m diameter
  • llath 2m long lath (B+C)
  • 60 laths

This option looks better, and I have been pondering on it with an additional wall, e.g. lattice wall from the yurt, yet the stability of the wall in this case isn't secured.


3V 5/9 Icosahedron Dome
3V 5/9 Dome with

  • 6.13m diameter
  • llath 2.5m long lath (B+C)
  • 83 laths

Very good head space, yet, the base line isn't straight, and some levelers are required.


4V 4/8 Icosahedron Dome
4V 4/8 Dome with

  • 6.3m diameter, llath 1.82m (D+D) bamboo with lhole 2-3cm
    • with total height of 3.1m it would be optionally to make another level, e.g. at 1.8m height for beds
  • 7.10m diameter, llath 2.10m (D+D) bamboo with lhole 2-3cm
    • with total height of 3.65m it would be suitable to make another level, at 2m height.
  • 8.05m diameter, llath 2.40m (D+D) bamboo with lhole 2-3cm
    • with total height of 4m it would be very obvious to make another level, at 2m height.
  • 125 laths

This I personally consider most nice as it's more smooth and less edgy, yet, the overhead for 250 struts becomes significantly now. In late winter/spring 2007 I started to build a 6.3m diameter 4V 4/8 dome with bamboo struts, consider to read my diary.

Connectors


Strut Connector
There are flat steel connectors with the form like:

With screws for wood and M10 screw the total cost per strut is about CHF 2.10 - 3.00, which brings the cost quite up, e.g. 4V 4/8 dome 7m diameter costs about CHF 510 or 330.

Thinking of using bamboo (with variable diameter naturally) is another option, costs apprx. CHF 0.35 per 182cm bamboo (@250 pieces) from a wholesale garden company.


Pipe Connector

In case of round profile struts (such as bamboo) another approach is to use a soft pipe as connector, like LD-PE and squeeze the one end. For variable diameter such as bamboo (or everything naturally grown) the half pipe is more suitable, adapting to variable diameter, using cable binder like this:


LDPE half-pipe with 1 cable binder (1)
2007/01/22 10:02
 
LDPE half-pipe with 1 cable binder (2)
2007/01/22 10:02
 
2007/01/22 10:08
 

The estimated costs are low, for half-pipe only few cents, and one screw per connection (not strut) plus the cable binder also a few cents. This approach with a LDPE pipe is suitable for lightweight tent-like setups, not recommended when the dome is covered with solid cardboard or alike.

Separate Functions

Some dome critics describe the problems to insulate the dome because of the many junctions and seams. An architect who worked on domes recommended to me to separate the functions:

  1. static
  2. thermal insulation
  3. water/weather insulation

then each part can be secured individually.

The problem only arises when all functions are targeted to be resolved with one solution, e.g. the static also must provide also water insulation and this is difficult.

Since I focus on "temporary buildings", buildings which can be put up and taken down within a short period of time such as 2-3 hours, this has to be kept in mind.

Cover


I haven't yet thought about it in all details, so far two approaches I consider:

  • water-resistant fabric stripes/leaf-like segments over the dome: cheap fabric, but might such cover hides the beauty of the dome then outside.
  • wood or cardboard triangle faces to cover entire dome, and use shingles to protects against rain leaking the many strut junction, but this would run against "temporary" building as it wouldn't be such one anymore.

So, the synthetic fabric for the cover seems my option, yet, the beauty of the architecture is covered and vanishes; also a complicated folding or sew pattern is required to have the cover fit closely.

If I use a rectangular blanket, then I require d * π / 2 side length.

4/8 Sphere Cover Calculator

This approach provides leaf-like composition to have a half-sphere roof canvas.

Symbols & Formulas:


α = 0 .. 90 cα = rα * 2 * π h = r * 2 * π / 4
rα = cos( α ) * r cαs = cα / nleaves y = h * ( α / 90 )

Edit the diameter d, and amount of segments nleaves, and the canvas lanes wide wcanvas which is used to patch together a leaf, and then press "calculate".

d = m, nleaves = , wcanvas = m, show segment(s),

The given canvas lane widths allows you to sew them together. In order to get a more exact shape, enter a smaller wcanvas and select "show one segment".


Half Sphere Surface

Which requires apprx. canvas.


Leaf composition: interior & rain canvas

Note: Since the calculator for now provides just 4/8 cover, I recommend:

  • 4/9 sphere: reduce it accordingly at the bottom
  • 5/9 sphere: add rectangular lane/stripe, in which you sew a cord which is used to make the bottom of the 1/9 of a 5/9 sphere fit closely (with wrinkels)

If you made experiences yourself with 5/9 sphere with leaf-like cover approach, drop me an email.

Sewing the Cover

In order to sew these leaf-like sphere surface together as rain cover, the water leak is particular to be avoided and so special care of how to sew the seams together:


Options of Seam Sewing

In case of the wigwam a combination of two of the options might be used:

  • overlay horizontal canvas stripes or lanes to compose a part of a roof leaf or segment
  • use either one-fold or two-fold to patch the leaves / segments together

Consider to seal the stitching holes from sewing with silicon or good clear tape for canvas (with threads) and preferable use water-resistant sewing thread as well.

4V 4/8 Geodesic Dome Model with Cover


4V 4/8 Geodesic Dome with leaf-like segment composed cover
As a test I did a cover for the previously build 4V 4/8 geodesic dome, d = 76 cm, nleaves = 6.

Step by step of the making of:


Getting the numbers from the 4/8 sphere cover calculator
2006/02/22 10:55
 
4V 4/8 Geodesic Dome Model
2006/02/22 10:56
 
Left-over from the yurt cover, PE (180g/m2)
2006/02/22 10:57
 
Marking the widths
2006/02/22 11:08
 

Cutting and folding half, leave some extra space for seam (two fold)
2006/02/22 11:10
 
Leaf/segment template finished with extra width for seam
2006/02/22 11:11
 
Marking other leaves/segments
2006/02/22 11:12
 
And so on ...
2006/02/22 11:16
 

Finished all 6 leaves/segments
2006/02/22 11:29
 
Using "two fold" to sew leaves/segments together
2006/02/22 11:50
 
Note that the top ending I didn't sew, it's too narrow
2006/02/22 11:50
 
Quick test if it roughly fits ...
2006/02/22 11:52
 

Adding more leaves/segments ...
2006/02/22 12:01
 
And so on ...
2006/02/22 12:18
 
Leaf composed 4/8 sphere cover finished
2006/02/22 12:23
 
4/8 sphere cover (side view)
2006/02/22 12:23
 

4/8 sphere cover (top view)
2006/02/22 12:24
 
Interior view of 4V 4/8 geodesic dome with cover (1)
2006/02/22 12:26
 
Interior view of 4V 4/8 geodesic dome with cover (2)
2006/02/22 12:26
 
Interior view of 4V 4/8 geodesic dome with cover (3)
2006/02/22 12:26
 

Interior view of 4V 4/8 geodesic dome with cover (4)
2006/02/22 12:27
 

As I experienced with this test for the 4V model, the top ending is hard to sew as the "two fold" seam is moderately thick, but overlaying 6 of them is too hard to sew, therefore I did leave it open. For a real life application a (clear) top cover would be build, e.g. a frame along the "top" 5 sided polygon of the 4V dome to hold the top cover.

Maybe I will extend the 4V Model further and test some ideas, let's see.

Windows & Door

A special consideration is the door, the triangle usually are too small to climb in (such as in case of a 3V 5/8), so a special strut combination might be use to extend a location to become the door, still triangular but large enough so one can enter the dome.

For now I consider to make the top most strut star covered by transparent plastic, and overlap the other cover, maybe use a four cords to fix the (square) sky cover, like in case of a yurt. Additional windows I will consider, but not yet sure about the weather/rain insulation of such. See my diary for the decision I actually made meanwhile.

Interior & Floor

Alike a yurt I will put a bright interior cotton cover as first layer, this way the construction is seen from the inside. Additionally putting in a wooden floor composed by laths or larger wooden plates.


Floor Examples

2nd Floor

With high ceiling making a 2nd floor for beds is an interesting option, in particular in the winter-time when the heat from the stove rises.


2nd Floor Options in Dome
A few options I quickly drew, keeping the circular shape of the dome for the 2nd floor as well:

  • "1/4 moon": 2 pieces and 5 columns, best light distribution from the skylight.
  • "3/4 moon": 1 or 2 pieces, 4 columns
  • "4/4 moon": 1-4 pieces, 4 columns
  • "eclipse": 1 or 4 pieces, 4+ columns, the light from the skylight reaches both levels, the 2nd floor and also the base.

Links

See also my notes on tipi and yurt.


(End of Article)

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