T-bar Dome

These are #10 X 5/8" Pancake head self-drilling screws. The self-Tapping (drilling ) screws are needed to screw threw the connector washer and t-bar steel strut. Other self-tapping screws can be used and this structure can be built without these connectors . The reducer washers are not something you find in the average hardware store. You will need to find a contractors Electrical Supply Store.

An extra pair of hands is always nice to have. Drywall carpenters work with light gauge steel studs all the time and will always have adjustable C-clamps. When using your self drilling screws you must have the steel clamped tightly together. These C-clamps come in 4" and 6" sizes and with and without feet. Any locking pliers will work. A pair of tin snips (metal cutting scissors) is needed to cut the light gauge T-bar steel. A cordless drill with a magnetic philips head screw tip works well for this project, but any drill motor with a screw tip will work.

The Drywall T-bar ceiling grid can be purchased at the local drywall supply store. It comes in boxes of 4' cross T's and 12' main T's. Once you know the diameter of the geodesic structure you will be building and have calculated the lengths using the cord formulas you can optimize the materials that will work best for your geodesic structure. The 24' T-bar steel geodesic structure optimizes the 4' cross T's with little to no waste.

In this connection system the T-bar struts will come together in the center of the 3" to 1/2" reducer washer. Center your reducer washer at the apex of the strut points. The sides will need to over lap each other so you can connect the two T-bar struts and the connector together with a screw. You will have to cut the corner off at lest one side of the T-bar strut to get the ends to meet in the center.

All your T-bar struts will be cut square or flat on the ends to proper length. During the construction you will cut the 60 degree angle off the corner necessary to create a tight fit and meet in the center of your connection. You will find one screw in the center of your strut will hold securely since all the struts are holding each other in alignment. This is your completed connection on the inside of the geodesic structure.

For the outside connection you will be using a larger reducer washer than you used on the inside. A 4" to 3" works well to center itself over the 18 degree angle that peaks in the center. The screws must penetrate the center of your T-bar and there is no way to clamp this connection for this process. Let the self tapping screw do the work and don't apply a lot of pressure. You will find that spinning the self-tapping screws at high speeds may burn up the cutting tip.

Spherical Geodesic Structures prefers using the 4V (frequency) Icosahedrons geometry to create geodesic structures. Unlike the 3V used by most dome manufactures the 4V has a horizontal flat line (great circle) at the hemisphere. This makes your foundation connection easier using the geodesic triangles. Once your structure is complete you can remove the area you have decided for your door.

The 4 frequency (V) uses smaller triangles than the 3V dome structures. This makes a stronger geodesic structure and also makes the components smaller, easier and safer to handle by one person during construction. Looking up at the center of the hemisphere you see the pentagon point of the five sided Icosahedrons pyramid.

Low cost housing at it's finest. The introduction to geodesic dome building. Light gauge steel T-bar (drywall) ceiling grid geodesic frame. Rigid foam insulation, waterproof stucco exterior and your choice of finished interiors. Ideal for a garage or small home. The material cost starts at under $1200. These are the smallest do-it-yourself geodesic dome kits that Spherical Geodesic Structures offers. All these products can be purchased at your local drywall supply store and fabricated by the owner-builder. These geodesic structures were designed to range under 30' in diameter or 900 square feet of floor space.

You will be starting from the bottom on your frame work with the D lettered struts. These bottom 20 struts will be of different material than the rest of the frame. The same Drywall Supply house will have wall angle that is used with the drywall ceiling grid or they may suggest you use 1 1/2" X 1 1/2" framing angle. These structure do not require to be built on a level surface and can be built on any surface. As you complete each row of triangles you will notice that the structure will begin to level itself and take shape. The bottom D struts will become flat and straight.

In our framing diagram you will notice all the A struts make up the Pentagons. The Icosahedrons geodesic structure uses the same major triangle to create the total geodesic frame. Start from the center of the pentagon where all five A struts meet and follow it down from the A-B-B-A struts to the next corner of the major triangle. Now if you travel horizontal across the A-B-B-A struts you will meet the third corner of the major triangle. Bellow this major triangle you have the same triangle turn upside down. You have five major triangles at the top of your Icosahedrons geodesic frame (the icosa cap). Around the middle of your spherical structure you have ten major triangles facing each other (the diagram below). And to complete the Spherical ball shaped structure you would have five major triangles (the Icosa cap) at the bottom facing up. In the major triangles there is what is called the Frequency ( the total number of struts from the pentagon center to pentagon center). Spherical Geodesic Structures uses the 4V (frequency) Icosahedrons A-B-B-A.

This diagram is to represent a 4' x 8' piece of foam or any other sheet material you wish to use. There are five triangles in the Spherical Geodesic Structures 4V geometry. In our T-bar geodesic frame we have optimized the 4' T-bar strut to build the 24' geodesic structure.

The diagram is showing one of the ways to optimize your sheet goods. You have five triangle combinations; A-A-C, C-C-C, B-C-D, D-D-E, E-E-E. You can save some time and materials by cutting the triangles to align the equilateral sides. The B-C-D triangle can be turned over (reverse) to optimize fabrication. You can glue the two end pieces together to create another triangle.

The cord lengths are calculated by multiplying the formula X the diameter you wish to build.

Example for the 24' diameter Spherical Geodesics Structures 4V dome.

A - 1.52 (30 struts) _____1.52 X 24' = 36.48 -- 36"-1/2"
B - 1.79 (30 struts) _____1.79 X 24' = 24.96 -- 25"
C - 1.76 (90 struts) _____1.76 X 24' = 42.24 -- 42"-1/4"
D - 1.88 (70 struts) _____1.88 X 24' = 45.12 -- 45"
E - 1.95 (30 struts) _____1.95 X 24' = 46.8 -- 46"-3/4"

Your measurements are calculated in decimals. If you round them off to the nearest 1/4" you should be fine. The 24' diameter was chosen because the longest strut is the E strut with a final length of 46-3/4". Using cross T's with a length of 47-1/4" we could not go much longer. The 30' diameter is ideally optimizes 10' strut material and 4' sheet materials. The 39' diameter optimizes 12' long strut materials. Light gauge steel has always been the superior building material over wood. The Spherical Designs Organization offers many prefabricated light gauge steel spherical structures for the owner-builder and general building contractors.