The walls can be curved or straight, domed with earth or topped with conventional roofs. Curved walls provide good lateral stability, forming round rooms and/ or domed ceilings like an igloo. Buildings with straight walls longer than 5 m (16.4 ft) in length need either intersecting walls or bracing buttresses or piers added. International standards exist for bracing wall size and spacing for earthen construction in different types of seismic risk areas, most notably the performance-based standards of New Zealand recommended by the ASTM International in their Standard Guide for Design of Earthen Wall Building Systems E2392 / E2392M – 10e1). Until more complete structural testing is available to correlate earthbag bracing need and performance to adobe, cement-stabilized buttresses and mortar anchors to hold barbed wire at stress points can be used for public buildings in high seismic risk areas.