A course or layer of impervious material which prevents capillary entrance of moisture from the ground or a lower course. Often called damp check. It allows evaporation from the inside of the building.
Design life is an important quantitative measure that defines the quality of the project.
Buildings will not last forever. The owner and designer should establish a reasonable design life for each project. This requires consideration of the economic factors such as initial cost and maintenance costs. The design life will have an impact on the selection of materials, maintenance procedures, and the selected factors of safety. The expected performance is also an important qualitative measure for the design of the project.