Domes evolved in deserts, so we recommend extra protection for snowy/wet climates. There are two main approaches: 1. Build a roofed dome. Search our Projects pages at Earthbag Building.com to see several examples. 2. Build a ferrocement rainscreen on the exterior of the dome. The rainscreen is basically an outer cement shell that’s built on top of the dome with about 1″ space between that allows any water that gets through to escape.
Directions: Add 1/4″ rebar pins 12″ apart on the exterior. Leave about 2” of rebar protruding above the surface. Then bend over the rebar at 90 degrees so about 1” is left protruding. Attach weep screed along the bottom. Plaster the dome before proceeding and add a moisture barrier such as elastomeric paint because cement plaster absorbs moisture. Tie plaster mesh or similar mesh to the rebar with tie wire and then cover with 2-3 coats of cement plaster.
Weep screed: This stucco flashing supports the stucco and allows water to drain out of the wall. Use a screened vent on top of the rainscreen that allows moist air to escape but keeps pests out.
Image source: First Choice Inspect.com