SR13 A survey of subfloor ground evaporation rates (2007)

Present building controls for subfloor moisture are based mainly on experience, with little explicit knowledge on the amount of ground water which must be disposed of or how this varies. This investigation, which forms part of BRANZ ongoing work on subfloor moisture problems, was undertaken to improve information on subfloor moisture evaporation rates.

This report describes the methods and observations of moisture evaporation rates from subfloor soils under New Zealand houses with suspended floors obtained in surveys from 1982-1984. The measurement in a pilot survey used both soil and free-water lysimeters, and in the main, survey free-water lysimeters only were used.

Measurements were taken in (nominally) 20 houses in each of three main centres - Auckland, Wellington,and Christchurch. They showed evaporation rates averaging about 300, 550, and 300 g/m² day respectively, with no clear seasonal variations.