Earth Bermed Houses

Had a chat with my friend Terry about his plans to buy property near Barry's Bay and build an earth-bermed house.  An earth bermed house is a type of efficient house design that takes advantage of passive solar for most of the heating requirements.  It also has natural cooling from its defining feature: earth-covered walls either from digging into the side of a hill or berming up soil around the structure.



We discussed the different earth-house options available to someone who doesn't want to waste money on energy bills (especially when those bills will rise indefinitely).  He told me about a concrete dome structure, a concrete block option and an earth ship.  The concrete dome option uses rebar and sprayed concrete (See shotcrete).  It can withstand a lot of weight and provides a waterproof barrier but it is expensive.

The concrete block option is something I hadn't heard of before.  You stack concrete blocks staggered, with no mortar.  Then you paste on a mixture of cement with fibreglass strands to hold it all together.  This has been used successfully in industrial applications (See surface bonded concrete).

The third option is the Earthship, which involves pounding dirt into old tires and arranging them in "U" formations (one for each room) facing South.  A wall of windows allows the sun to heat the floors and walls, releasing that energy throught the night.

Each of these options capture and store the sun's energy using thermal mass.  Any object has thermal mass, but cement has the most.  People have used containers of water, sand-filled crates or walls, slate, stone, masonry or brick to hold thermal energy.  The amount of thermal mass you need can be figured using a formula found in many books on Solar Homes.  It is very important to use the correct "window to mass" ratio or your home will be too hot or not hot enough.

Several mistakes have been made with passive solar houses and many improvements have been discovered.  One common mistake was not putting insulation between the cement and the earth thus allowing an infinite heat sink.  It would just keep absorbing all the sunlight energy it was given.  Other problems were caused by that wall of windows - too much window and not enough mass to absorb the energy.  This produced over-heated homes.

One doesn't have to live underground though to obtain an efficient house.  See my post on the German Passive House.