Geodesic Dome Covering Patterns

Geodesic Dome Covering Patterns

The dimensions provided here are for a class-1 frequency-2 icosahedral geodesic dome with a floor diameter of about 201 inches.

The 6-inch seam allowance or "tab" areas (indicated as the region between solid cut lines and dashed edge lines) are wider than the standard tarp grommet seam width. The intention here was to create separate overlapping pieces with 2-inch wide margins for overlap and 4-inch wide margins for error in placement of the grommets. An alternative would be to join the pieces at appropriate edge lines, in which case smaller tabs could be used.

Pentagon Triangle

Pentagon triangle.

This is a basic isosceles triangle pattern used to cover a single triangle within a "pentagon". Note that this pattern will not fit over any of the equalateral triangles which are outside a "pentagon".

(Here "pentagon" refers to a collection of five identical acute-angled isosceles triangles joined along their short edges, such as at the top of an icosahedron or icosahedral geodesic dome. The actual shape is technically not a pentagon because it is three-dimensional, not two-dimensional. Still, the shape reminds one of a pentagon and the name "pentagon" is shorter than "hexahedron with five identical isosceles triangles and one regular pentagon" which is a more accurate description. To see an example of the "pentagon" refered to here, look at the schematic diagram of a frequency-two class-one hemispherical icosahedral geodesic dome and look at the shape created by vertices 1-6.)

This "pentagon" triangle pattern is part of the basis for several other dome cover patterns.

To use this pattern to create the other patterns, measure onto large paper or fabric the inner triangle (drawn with dashed lines) and cut out that triangle. Alternatively, cut out the larger triangle and perforate your pattern along the dashed edge lines to allow for marking through the perforation. To construct a triangle, follow these steps:

• Using a long straight edge or a measuring tape, measure the bottom line segment. The length of the line segment should be equal to the length between bolts on the longer poles of the geodesic dome. For the example shown, the line length is 62 inches.
• Using the endpoints of the first line segment as the centers of imaginary circles, draw circular arcs with a radius equal to the length between bolts of the short poles of the geodesic dome. In this example, the radius is 55 inches. The place where those circular arcs intersect marks the final vertex of the triangle. Draw lines from that intersection to each of the endpoints of the first line segment.

  (To draw a large circle, use a piece of string and a pen: Hold one end of the string to the center of the circle. Measure the string to the desired radius of the circle. At that point, tie a secure knot and place the tip of a pen into the knot. With the string taught, draw the circle. Make sure the pen angle does not change while drawing.)

Equalateral Triangle

Equalateral triangle.

This is a basic triangle pattern used to cover one equalateral triangle outside one of the "pentagons". Note that this pattern will not fit over any of the isosceles triangles which are inside a "pentagon".

As with the "pentagon" triangle, this equalateral pattern is part of the basis for several other dome cover patterns.

The patterns below consist of these basic triangles. Once you have basic triangle patterns, construct other patterns by appropriately placing the basic triangles on a large sheet of fabric and tracing the outline of the basic triangle.

Divided Original Triangle

Divided Original Triangle
(Click image for larger version.)

This is a pattern used to cover an entire divided original triangle. A divided original triangle is one of the complete polygons based on the division of an original triangle in the original platonic polyhedron. In this case, that is one of the original triangles of the icosahedron.

Using five copies of this design one could cover the top two of three tiers of a class-1 frequency-2 icosahedral dome.

Note that this pattern is technically not a triangle -- it is an irregular hexagon made of four triangles: one equalateral (in the center) and three "pentagon" triangles (around the equalateral).

The "divided original triangle" complements the "geodesic strip" pattern. Using five of each of those patterns would cover and entire hemispherical frequency-two class-one icosahedral geodesic dome.

You can easily make an accurate template for this pattern by connecting dome poles in the layout of this pattern. This method reduces accumulated errors that using a ruler would introduce. This method also eliminates the confusion of what size edges to use for dome sizes other than that used in the calculations in this page.

Geodesic Strip

Geodesic Strip
(Click image for larger version.)

This is a basic geodesic strip pattern used to cover part of a line along a geodesic perimeter.

Note that this pattern consists of 4 of the basic triangles: one equalateral (on the left) and three "pentagon" triangles.

The "geodesic strip" complements the "divided original triangle" pattern. Using five of each of those patterns would cover and entire hemispherical frequency-two class-one icosahedral geodesic dome.

You can easily make an accurate template for this pattern by connecting dome poles in the layout of this pattern. This method reduces accumulated errors that using a ruler would introduce. This method also eliminates the confusion of what size edges to use for dome sizes other than that used in the calculations in this page.

Frequency 3 icosahedral symmetry triangle

Freq-3 symmetry triangle
(Click image for larger version.)

This is a symmetry pattern used to cover one of the symmetry triangles of a frequency-3 geodesic.

Note that this pattern consists of nine of two basic triangles: three smaller (at the corners) and six larger triangles (in the center).