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Evolution of sub-floor moisture management requirements in UK, USA and New Zealand 1600s to 1969

Nigel Isaacs (School of Architecture, Victoria University of Wellington, Wellington, New Zealand)

International Journal of Building Pathology and Adaptation

ISSN: 2398-4708

Article publication date: 21 June 2019

Issue publication date: 31 July 2019




The purpose of this paper is to review the historic development of the requirements for sub-floor (also known as “basementless space” or “crawl space”) moisture management in the USA, UK and New Zealand (NZ) from 1600s to 1969.


The review of 171 documents, including legislation, research papers, books and magazines, identified three time periods where the focus differed: 1849, removal of impure air; 1850–1929, the use of ground cover and thorough ventilation; and 1930–1969, the development of standards.


Published moisture management guidance has been found from 1683, but until the 1920s, it was based on the provision of “adequate” ventilation and, in the UK, the use of impermeable ground cover. Specific ventilation area calculations have been available from 1898 in the UK, 1922 in the USA and 1924 in NZ. These are based on the area of ventilation per unit floor area, area of ventilation per unit length of perimeter wall, or a combination of both. However, it was not until 1937 in the USA, 1944 in NZ and after the period covered by this paper in the UK, that numerical values were enforced in codes. Vents requirements started at 1 in. of vent per square foot of floor area (0.7 per cent but first published in the USA with a misplaced decimal point as 7 per cent). The average vent area was 0.69 per cent in USA for 19 cases, 0.54 per cent in NZ for 7 cases and 0.13 per cent in UK for 3 cases. The lower UK vent area requirements were probably due to the use of ground covers such as asphalt or concrete in 1854, compared with in 1908 in NZ and in 1947 in USA. The use of roll ground cover (e.g. plastic film) was first promoted in 1949 in USA and 1960 in NZ.

Practical implications

Common themes found in the evolution of sub-floor moisture management include a lack of documented research until the 1940s, a lack of climate or site-based requirements and different paths to code requirements in the three countries. Unlike many building code requirements, a lack of sub-floor moisture management seldom leads to catastrophic failure and consequent political pressure for immediate change. From the first published use of performance-based “adequate” ventilation to the first numerical or “deemed to satisfy” solutions, it took 240 years. The lessons from this process may provide guidance on improving modern building codes.


This is the first time such an evaluation has been undertaken for the three countries.



The work of Bill Rose on the development of US requirements is gratefully acknowledged. This paper could not have been written without the support of Fulbright NZ Scholarship October 2016 to February 2017, and that of Victoria University of Wellington and the Bartlett, University College London for Research and Study leave in 2015.


Isaacs, N. (2019), "Evolution of sub-floor moisture management requirements in UK, USA and New Zealand 1600s to 1969", International Journal of Building Pathology and Adaptation, Vol. 37 No. 4, pp. 366-394.



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