One of the goals in ecologically sustainable development (ESD) is to reduce energy demand in buildings. Occupant comfort then needs to be achieved with minimum assistance from mechanical systems. Such buildings depend on the effective performance of the building itself to maintain comfort. 'Passive solar' is the best known general design approach achieving these goals. This Note reports on 'climate responsive' design principles in hot arid locations. It considers the approach to, and elements of, low energy design of buildings for comfort where 'passive solar' alone is not the full answer.