Our Concrete Hobbit Home Dome Technology Explained
This is a very brief explanation of the technology we use to build concrete domes. Concrete domes can be made in various shapes and sizes. Some are high, some low. Some are simple circles, others are ellipses, peanut shapes, or a series of various rooms connected by tunnels.
Below is a basic description of the process we take to build a simple circular concrete dome shells often used for our custom hobbit homes. More complex shapes use the same technology and construction steps. This is the best way to build a concrete dome because it eliminates condensation, maximizes energy savings, and is unbelievably strong.
Our 4 Step Hobbit Dome Building Process
Spraying 3” of dense closed-cell foam on the inside of the form provides a moisture-resistant R-60 insulation barrier. Most conventional buildings leak heat through the uninsulated studs, which are 15-20% of the area of a wall. With this technology, our concrete domes really only lose significant heat through doors and windows. More insulation than the 3” can be used, but it’s not worth the extra money for a tiny fractional improvement. If the building is underground, then the earth on top and sides of the building also reduces the heat loss because the frigid air never touches the building.
Rebar hangars are embedded in the last layer of foam, and rebar is tied off to the hangars. The latitudinal and longitudinal rebar strengthens the concrete in all directions of tensile forces. It is not shown in this image, but extra rebar is installed around all door and window openings according to specifications by engineering. Forces are magnified around openings. Rebar sizes and spacing are matched to the project design specifications. The rebar does not touch the foam and gets completely encapsulated in the concrete layer of the dome.
A high strength shotcrete mix is sprayed layer by layer to a thickness of 3” minimum. Larger domes have more inches of concrete and larger diameter rebar, all of which are specified by our engineers during the design phase of your project. This technology requires a special pump and nozzle to apply the mix – it is not the same equipment used by typical shotcrete or gunite installers who build custom swimming pools. The result is one of a kind. The thermal mass of the concrete backed up with insulation provides strength and energy efficiency unmatched by conventional buildings.
The concrete dome interior is somewhat rough when sprayed. Possible finishes are to leave it natural (reduces some echo), a trowel is smoother (for appearance, not strength), or to hide it with interior finish options. All conduit for electrical and plumbing needs is set within the floor and walls during the dome shell construction process. Walls can be framed in wood or metal studs and finished with drywall or any other wall/ceiling covering desired.