Earthen walls do well in white areas of BSI's map

Minimal Strength

Where quake forces are likely <0.25 g or less, traditional earthen huts last hundreds of years unless they decay. Use water-resistant base courses and a roof overhang to prevent damage.

Earthen buildings moderate humidity and temperature swings. Techniques include traditional adobe, puddled adobe, cob, rammed earth and compressed blocks as well as most kinds of plastered earthbag. 

Basics:

More wall than window

Firm footing and moisture break

Walls thick enough for the height

Stiffen long walls with buttresses 

Connect walls well under good lintels and bond beam

Basic best techniques for low risk areas (light gray on BSI's map)

Limited Strength

Where quake forces are likely 0.25- 0.6 g, build with soil at least 1,8 MPa (190 psi) strength. Use field tests to check.

Interconnect footings and walls strongly. Keep stub walls less than 1.2 m (4') long. Space intersecting walls or buttresses regularly every 10- 20' (3- 6 m). Check bracing using information from New Zealand's non-engineered building code (NZS 4299).

Construction details for adobe and rammed earth are included in free versions of NZS 4299 online. Details for compressed block walls are included in the 2020 revised NZS 4299.

Use conventional earthbag techniques with strong (2,1 MPa/ 300 psi) soils. For minimum strength soils, earthbag needs splices linking inserted rebar, or improved reinforcement.

Free Low-Cement CE Construction pdf 

Special reinforcement for medium- high seismic risk (dark gray/ black on BSI's map) 

Moderate or High Strength

Brittle wall types like most adobe, compressed block and rammed earth must be intensively reinforced on continuous reinforced concrete footings.

More flexible wall types may use footings of gravel bag with wire binding. These include cob and reinforced ICEB (interconnected compressed earth block) as well as improved earthbag. (Use cob in cool areas to protect its natural fibers).

Earthbag's higher ductility requires  less manufactured reinforcement than other walls, but it needs tubes of strong soil with interconnected steel. Use spot corner reinforced concrete (RC) footings or confining RC grade beams.

Free Standard Grade CE Construction pdf

High Strength CE pdf coming soon.