Last weekend, I had the pleasure of meeting Lloyd Turner and seeing his beautiful home in Boulder Creek, CA. Here refers to design as "soap bubble" architecture, where the inside edges are straight and the outside is round - this is one of nature's inherently strong and efficient shapes. It is also important to note the rooms/bubbles are torispheres, not hemispheres (i.e. domes) - unlike a dome, a torisphere's walls do not arch in until they are close to the ceiling giving you full use of the floor plan below.From the outside, only the top of partially buried domes emerge from the earth like they were grown there. Inside the rooms are warm and comfortable. A wood burning stove kept the house warm, while skylights provide plenty of light. Built in 1982, the house is in as good of condition as the day it was built thanks to its strong foundation, subterranean drainage system, and inherently strong design. Lloyd also had to design the operable skylights, round egress windows, and more.
Lloyd's construction technique:
Unlike Monolithic Dome or other air-form techniques that require extremely strong membranes, high powered fans, and airlocks, Lloyd's design uses simple Tyvek fabric and inflated with a fan - no airlock is needed for this low pressure air form. Instead he applies increasing thick layers of polyurethane foam - allowing each layer to start to set up and create the structure as he goes. In this construction photo - the first layer of foam is applied so thin the shadows of the tree branches can be seen through it. By the time he got to end he could start the next layer and within 4 layers he was able to get to 4" of foam. With 4" of foam the form is much stronger and it can hold the weight of 3/4" of shotcrete without deforming and the same layer process is continued, with a day between layers, until 2" of concrete is applied. Thus, Lloyd got the structure to "grow" with ever increasing layers until the structure was 6" of foam and concrete, all with a simple light weight air-form. Tyvek was used because it does not need to be removed after construction (the moisture can escape and it can be stuccoed over) and the gores (see airform panels design link below) can be taped together.
The airform created the concave exterior walls and roof. Temporary 1"x4" boards were used to maintain the proper arch on the top of the straight interior walls. Once the foam was sprayed onto the airform the wood framing was replaced with structural concrete insulated panels (SCIPs) similar to the ones we sell at BuildFast. Then re-bar ribbing was added at the connecting points of the airform and SCIPs to give it extra strength. The metal fiber reinforced shotcrete is then sprayed in successive thin layers to the underside of the foam domes until the required thickness is achieved. It doesn't take any longer to quickly apply several thin layers as it does to apply the full thickness while standing in one spot. Thus a a unique structure that will last for generations was built with a simple low pressure inflated form. For more info on the process check out Flying Concrete's page on the house.
Links with photos, design math, and more:
Update - Lloyd asked me to add one more thing:
If you pour the foundation only (no slab) first, then spray the walls and ceiling - any concrete that falls/bounces off can be covered and incorporated into the slab when it poured at the end. Also to note, the electrical and plumbing were all put into the slab as well. Hope this helps.
