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Void conditions and potential for mould growth in insulated and uninsulated suspended timber ground floors

Sofie Pelsmakers (Arkitektskolen Aarhus, Aarhus, Denmark)
Evy Vereecken (Faculteit Ingenieurswetenschappen, Katholieke Universiteit Leuven, Leuven, Belgium)
Miimu Airaksinen (Suomen Rakennusinsinoorien Liitto, Helsinki, Finland)
Cliff C.A. Elwell (University College London Energy Institute, London, UK)

International Journal of Building Pathology and Adaptation

ISSN: 2398-4708

Article publication date: 19 October 2018

Issue publication date: 31 July 2019




Millions of properties have suspended timber ground floors globally, with around ten million in the UK alone. However, it is unknown what the floor void conditions are, nor the effect of insulating such floors. Upgrading floors changes the void conditions, which might increase or decrease moisture build-up and mould and fungal growth. The purpose of this paper is to provide a review of the current global evidence and present the results of in situ monitoring of 15 UK floor voids.


An extensive literature review on the moisture behaviour in both uninsulated and insulated suspended timber crawl spaces is supplemented with primary data of a monitoring campaign during different periods between 2012 and 2015. Air temperature and relative humidity sensors were placed in different floor void locations. Where possible, crawl spaces were visually inspected.


Comparison of void conditions to mould growth thresholds highlights that a large number of monitored floor voids might exceed the critical ranges for mould growth, leading to potential occupant health impacts if mould spores transfer into living spaces above. A direct comparison could not be made between insulated and uninsulated floors in the sample due to non-random sampling and because the insulated floors included historically damp floors. The study also highlighted that long-term monitoring over all seasons and high-resolution monitoring and inspection are required; conditions in one location are not representative of conditions in other locations.


This study presents the largest UK sample of monitored floors, evaluated using a review of current evidence and comparison with literature thresholds.



This research was part-funded by the EPSRC Centre for Doctoral Training in Energy Demand (LoLo), grant numbers EP/L01517X/1 and EP/H009612/1 while the corresponding author was at UCL. The authors are also very grateful for the support of the Belgian Chair Charity Fund administered by the Embassy of Belgium in London. These financial supports are gratefully acknowledged. The authors are grateful to the homeowners for access to the case study house and to the following organisations: Salford City West Housing Association, Carbon Co-op, NBT and Downs Energy for insulating Floor 8.


Pelsmakers, S., Vereecken, E., Airaksinen, M. and Elwell, C.C.A. (2019), "Void conditions and potential for mould growth in insulated and uninsulated suspended timber ground floors", International Journal of Building Pathology and Adaptation, Vol. 37 No. 4, pp. 395-425.



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