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Hot-box measurements to investigate the internal convection of highly insulated loose-fill insulation roof structures

Research output: Contribution to journalArticleScientificpeer-review


Original languageEnglish
Article number109934
Number of pages10
JournalEnergy and Buildings
Publication statusPublished - 1 Jun 2020
Publication typeA1 Journal article-refereed


The purpose of this study was to investigate how internal convection in loose-fill insulations affects the insulation properties of highly insulated roof structures. This study consists of laboratory measurements of roof structures insulated by two different blown-in insulations. The measurements are repeated with two temperature differences and air velocities for 300 mm and 600 mm thick insulation layers both with and without trusses, making a total of 24 case studies. The measurements were conducted with equipment using the calibrated hot-box method. The results of the tests show that internal convection can reduce insulation capacity significantly, especially with low-density loose-fill insulations, such as blown-in glass wool. A critical evaluation should be performed as to whether international standards and national building regulations take internal convection into account adequately. According to this study, 5 should be used as a critical modified Rayleigh number for horizontal roof structures with an open upper surface when used insulation material is loose-fill glass wool or wood fibre insulation as in this study.


  • Calibrated hot-box, Heat transfer, Internal convection, Laboratory measurements, Roof structures, Thermal insulation, Thermal transmittance

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Field of science, Statistics Finland

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