New guidelines for use of convection barrier in roofs
Buildings that are designed to meet high energy-performance requirements, e.g. passive houses, require well-insulated building envelopes, with increased insulation thicknesses for roof, wall and floor structures. Increased insulation thicknesses may lead to increased risk of mould growth and moisture damage. One reason for this is increased risk of natural convection in the insulated cavities causing moisture redistribution of, for example built-in-moisture in the timber frame. Natural convection inside highly insulated structures also significantly increase the heat transmission of roof structures.
In order to reduce the risk for natural convection, introduction of a vapour open convection barrier is recommended when the insulation thickness exceeds 200 mm, also for pitched roof structures.
Gullbrekken, L, Uvsløkk, S, Kvande, T & Time, B: Hot-Box measurements of highly insulated wall, roof and floor structures. Journal of Building Physics 2017, Vol. 41(1), p. 58-77; doi:10.1177/1744259116669516, ISSN 1744-2583
Gullbrekken, L: Climate adaptation of pitched wooden roofs. Doctoral theses at NTNU, 2018:124, Norwegian University of Science and Technology, Faculty of Engineering, Department of Civil and Environmental Engineering. ISBN: 978-82-326-3038-7