The Dome: A Sturdy Bubble of Wooden Triangles

The geodesic dome, invented by Buck minster Fuller in 1951, ingeniously com bines equal-sided isosceles triangles into a pattern of hexagons and pentagons to form a hemisphere that's larger and stronger than any conventional structure that can be built with the same quantity of identical materials.

A dome like the one shown easily built of 1-by-1 wooden struts stapled together, is cheap, strong, attractive and versatile. It can span up to 30 ft. without internal bracing, making it ideal for almost any back yard shelter calling for light, airy, uninterrupted interior space. It makes a fine cover for a swimming pool to keep out airborne debris and to warm-the water by trapping solar heat. A door or window can be created simply by hinging one of the dome’s triangles; to keep the structure strong, never hinge two adjacent triangles.

This particular dome is a fair-weather structure, difficult to leak-proof but easy to disassemble for off-season storage. Building it involves three simple, repetitive operations: cutting the struts, assembling them into triangles and attaching the triangles to one another. Cutting the struts to the right length is a matter of applying the table at right; mitering strut ends to the correct angles is easy to do with a homemade jig.

The angles given for the strut ends will result in triangles with slight gaps at the corners opening to the inside of the tri angle frame. This assures that the tips of the struts will meet and the outside dimensions of the triangles will be exact.

Before assembling the dome, prepare its cover by wrapping each triangle with a flexible covering or attaching a triangular piece of plywood or solid plastic. Use flexible, ultraviolet-resistant plastic on light-trapping domes for pools and gar dens, colored plastic for a shade house. Plastic screening keeps bugs out and wire mesh keeps birds out—or in.

Plastic-sheathed domes can be partly weatherproofed by sealing all joints with plastic tape, but will still leak around windows and doors. As plastic or other covering deteriorates, replace it by re moving and recovering affected frames.

In windy locations, cut 3” hard- board reinforcement disks with a hole saw and screw them to the struts where the points of triangles meet, using one 1” wood screw per strut.

86 A homemade hemisphere. The dome shown here is composed of two sizes of triangular wood en frames made from straight, knot-free 1-by-1s. It is covered with clear plastic and has hinged vents and a door opening. Seen from above, the dome is a pattern of pentagons formed from short triangles (gray), and hexagons formed from tall triangles (white). Each kind of triangle has two legs of equal length and a base of a different length. The bases are the heavy lines of the inset; the legs converge at the centers of the hexagons and pentagons. The lengths of the legs and bases vary with the size of the dome but the angles at which they meet (Step 1) are always the same.

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Finding the Lengths of Struts for a Dome: Diameter of dome; Height; Tall triangle struts base, leg; Short triangle struts leg base;

Domes cut to order.

Cutting and Assembling the Framework

1. A jig for struts. Miter 1-by-1lumber to the angles indicated in the inset above and to the lengths determined by the table (above, top) with a radial arm saw, a table saw or with a circular saw used in the homemade jig shown above at left. To make the jig, bracket a 1-by-1 with 1-by-4s nailed on a sheet of plywood; remove the 1-by-1. Nail a 1-by-2 fence across the 1-by-4s at the angle of the first cut you will make. Guide the saw along the fence to cut a kerf through the 1-by-4s, then measure back from the kerf to position a stop-block. Saw all the struts that require cuts at that angle, then move the fence, cut a new kerf and reset the stop-block as needed for other struts. Mark the strut ends with their angles.

2. Assembling the triangles. To form each of the 30 short and 45 tall triangles required, lay out three struts as shown above, hold two tips together and drive three staples across the joint with a heavy-duty staple gun. Similar fasten the third strut, then turn the triangle over and triple-staple each joint from the other side. Paint the triangles.

88 3. Covering the triangles. Lay a triangle on a sheet of plastic, fold the plastic up over one strut and staple it near a corner. Stretch the plastic slightly along the strut to a second corner and staple it. Repeat for the other two struts; avoid leaving wrinkles at the corners. Then gently stretch the plastic and staple it to the rest of each strut, starting at the middle and working to the ends. Trim off excess plastic.

To cover a triangle with thin plywood or other solid material, lay the triangle on the material and trace around the edge. Cut the material along the traced lines and fasten it to the triangle with weatherproof staples, nails or screws.

4. Assembling the first course. At a level site, hold two tall triangles edge to edge with their bases oriented as shown. Align the corners and staple the two inside edges together every 4 to 6”. Attach a third tall triangle to the right side of the second, oriented as shown in the inset. Continuing to the right, similarly attach three short triangles with the bases oriented as indicated in the inset. While helpers hold the triangles upright, add four more sets of tall and short triangles to the first set to form a circular fence leaning inward, with its plastic-covered side outward; staple the last triangle to the first.

Measure along the ground from the middle of the base of a short triangle to the point opposite it where the corners of three tall triangles meet near ground level. Make similar measurements in different directions and adjust the assembly of triangles to make all the measurements equal.

5. Staking down the dome. Drive a 2-foot-long 2-by-2 wooden stake treated with a preservative into the ground alongside the middle of the base strut of a short triangle — one of the five points at which the dome’s base sits firmly on the ground. Secure the stake to the strut with a 3” wood screw. Similarly stake down the struts of the other four short triangles.

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6. Finishing the dome. Following the pattern in the inset, install additional courses of triangles. Use a helper to hand in triangles, to help position them and to hold a block of wood opposite the staple gun to assure that the staples penetrate well. Have two others help keep the sides of the dome upright until you have completed the second course. When the sides of the dome rise too high to pass triangles over, make an opening in the dome by removing a tall base-down triangle from the first course. In stalling the last few triangles may require you and your helper to stand on stepladders. If the last pair of triangles does not fit, release the dome from the stakes to fit the triangles in.

7. Making a door. Reattach with hinges the tall triangle you removed during construction. Reinforce with vinyl tape the opening edges of the door and the edges of the adjacent triangles that form the unhinged side of the doorjamb. Screw strips of wood to the jamb to form a door stop. Latch the door with hooks and eyes.

Similarly make hinged windows. Alternatively, door and window openings can be made simply by removing individual frames.