In the northern hemisphere the classic earth-sheltered plan exposes the south face entirely and berms the other three walls, so the glazed south wall provides both daylight and passive solar heating. In the southern hemisphere the sunward face is north, and the same wall needs shading in summer and insulating shutters on cold nights.
A south-facing glazed wall is the one open face of a bermed building, giving winter sun to the interior and thermal mass.
The Open Face Is Both The Heater And The Weak Point
Glass lets winter sun in; the earth mass behind and the floor store the heat and give it back at night, as Passive Solar Building Design explains. The same glass loses heat quickly on a cold night and overheats the room in a summer sun, so the open face needs shade overhead in summer and insulation at night. The earth on the other three sides gives the room its steady temperature.
What You Need
- Glazing: salvaged window glass, or glass made by spinning, or oiled linen and animal membrane before glass; see Flat Glass and Window Design.
- A shading overhang over the glazed face for summer sun.
- Insulating shutters or heavy curtains for night.
- A high-mass floor and back wall inside to store the heat.
- Berming and drainage on the other three sides; see Bermed Walls.
Method: Orient, Shade, Store
Step 1: Find true south (north in the southern hemisphere) and set the open face to it.
Step 2: Size the overhang so that high summer sun is shaded and low winter sun enters. This depends on latitude; check the sun angles for your site before building.
Step 3: Put thermal mass in the floor and the back wall where the sun falls.
Step 4: Seal and insulate the frame, and fit shutters.
Step 5: Arrange an air path so that excess heat can leave in summer; see Ventilation and Light.
Common Mistakes
- No summer shade. The room overheats.
- No night insulation. The glass drains the stored heat.
- Glazing facing the wrong way for the hemisphere.
- Glass without a frame that drains. Water sits in the sill.
Safety
Glass breaks and glazing carries earth loads
Do not berm earth against the glazed face, and keep the frame separate from the earth roof load. Handle glass with gloves and eye protection, and set it so a fall does not bring the roof edge with it.
What’s Next
- Learn next: Earth-Covered Roof Living Spaces
- Combine with: Pre-Heated Thermal Mass — storing heat in dense material