Residential Dome Designs

DOME MAGAZINE:  Spring 1991, Vol. 3 | No. 4

Why would you ever opt to consider such a radical design for a home?

This question has been asked on many occasions since I first entered the area of spherical housing in 1975. I must admit that I was originally a longtime fan of Buckminster Fuller, but the energy crunch was on in the mid-seventies, and this looked like a viable answer to the, then, high costs and projected higher costs of home heating and cooling.

 This discourse will generally cover our experience of dome manufacturing and constructing in the vigorous climates of the Midwest and Canada, but is not limited to that area, since we have provided double-walled, super-energy efficient domes in all areas of the United States, including the southwest Texas desert (Midland) as well as Alaska.

Energy Structure, Inc. Objectives

This experience has been more than satisfying in terms of results. We were able to achieve our stated goal, which at that time was to provide less expensive housing that embodied the maximum of energy savings. That stated goal, ten years ago, is still applicable today.

First, to achieve a lower building cost by the use of standard building materials. Standard building material costs would be less because of the volume of their use  (in conventional homes). This material use, rather than unconventional and more expensive, exotic materials (plastics, metal sheets, etc.) means lower building costs. The dome concept itself uses less material because of its basic design.

Second, the use of the double-walled energy strut allowed for two six” bats of un-faced fiberglass insulation, another low-cost standard building material, maximizing the R factor to a nominal 42 at a very low cost per square foot without substantially increasing the cost of the structure. Since the ratio of dome surface area to floor space is substantially less than the grid house, the savings in energy costs have proven to be substantial.

Best of all, these past sixteen years have been a constant learning experience, an experience that was a direct result of hands-on operations. Working directly with owner-builders and building contractors, along with architects and engineers, has provided valuable information that is simply not available through conventional educational channels (books, trade schools and architectural courses, etc.).

The Need for Conservation      

We have been deeply disappointed in our government’s refusal to recognize the need for energy conservation during the past ten years – specifically, by the killing off of all the energy incentives that were available for energy saving practices at the beginning of the decade and the canceling of all alternative energy research and development programs that were in full force at that time. This, no doubt, was as a result of pressure from the oil lobby. It is doubly disappointing because that apathy toward energy conservation was passed on to the housing industry in general.

Today, and in the future, because of ever-increasing energy costs, the homeowner must pay dearly for this deliberate destruction of energy-saving options. Many of the problems that have occurred with dome systems during the past fifteen years can be directly traced to a lack of information on the basic operation of the structure itself. Trying to match conventional, rectangular grid housing practices with dome construction in many areas of design simply does not work, particularly in the areas of foundations, insulation, and dome mechanics (ventilation, heating and cooling).

The Basic Laws of Physics

It is always a disappointment to see basic laws of physics denied or ignored. We will explore the fundamentals of dome mechanics later in this article. First, let’s look at the dome structure itself. There are several designs for the geodesic dome that are available from a number of manufacturers. Generally, they are categorized into two basic systems. One is the hub and strut system, and the other is the panelized system. Let me explain.

We will try to base our observations on an objective plane and to cover some of the advantages and disadvantages of each design. All of these designs represent major advancements in the area of housing. Either type of dome system, if done well, represents major benefits to the dome homeowner.

Basic Dome Systems

The hub and strut system consists of dimension lumber (2 x 6) with connecting hardware attached to the struts. The struts are connected to metal  hubs and can be assembled with a 1/2” socket and a 3/8” ratchet. The exterior skin, usually CDX plywood, is nailed to the struts after the framework is in place. This is the relatively easy part of the dome building schedule, as the average 1200-square-foot dome shell can be erected in less than a day with three or four semiskilled workers. The exterior panels are precut and can be nailed in place in another two days. There is no heavy lifting, as the parts are light enough for one person to lift in place. All parts are color coded for easy identification.

The panelized system consists of triangular panels that are factory manufactured using 2 x 4 or 2 x 6 framing members with the exterior plywood in place. The insulation factor is controlled by the thickness of the strut wall. So in the panel system, the insulation is limited to 3 1/2” with the 2 x 4 framework and 5 1/2” with the 2 x 6 framework. In certain areas of the country, these wall thicknesses provide adequate insulation factors. Since the panels are assembled in the factory, it is usually necessary to have a crane available to lift the panels in place. The dome shell can be erected in two or three days or less.

Dome Strength

Let’s look at the structural strength of the geodesic dome. Manufacturers of both hub and strut, and panelized systems, by and large, have done the testing and engineering necessary to determine the ultimate loads that their particular design will sustain. These test results prove, without exception, that the geodesic dome structure far exceeds the capabilities of conventional housing to withstand snow loads, wind loads and particularly, seismatic stresses. But who considers buying a home because it is strong and safe? Probably not many, unless they live in the path of a hurricane or over an earthquake-causing fault. Sadly, the housing industry, in general, is only interested in minimum safety standards.

The geodesic dome consists of triangles, the strongest of all geometric building forms. When incorporated into the sphere, the structure becomes far stronger and safer than conventional housing. If you believe that earthquakes do not cause deaths but that buildings do, you must consider dome system homes.  So much for design strength.

What Makes Domes Tick

Let’s examine some of the features that make domes tick. While it is true that a dome functions environmentally well because it has natural circulation due to its openness, it is also true that this natural circulation feature does not play the best under actual living conditions.

When warm air is introduced at the lower level of the dome, the natural law of convection comes into play. Warm air rises. In practice, the actual living conditions of a dome, what happens? If nothing is done with that warmed air at the dome top, the upper rooms of the dome become uncomfortably warm. If nothing is done to relieve this situation, the extra BTUs from the collected warmed air at the dome top are bled out through the wall/roof and are lost through a second law of applied physics, that of conduction. When enough BTUs are lost to cool the air, natural circulation comes into play, and the cooled air is returned to the lower levels, again by the laws of convection. It must then follow that the natural air circulation has two drawbacks.

First, the upper levels are uncomfortably warm compared to the lower levels. Second, the extra BTUs that have collected at the dome top are conducted out through the wall/ceiling and are lost, and no benefit is obtained from them.