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Doctoral student Klaus Viljanen from the Department of Civil Engineering received one of five awards for best publication for his article Hygrothermal Behavior of Ventilation Cavities in Highly Insulated Envelopes at the Nordic Symposium on Building Physics, held 7­–9 September 2020. A total of 254 scientific articles were presented at the event, which is the largest international conference on building physics.

The article deals with the performance of ventilation cavities in modern wood-clad exterior walls and roof structures that are both highly insulated. Long-term measurements showed that high insulation level can lower the temperature in the ventilation cavity, which increases relative humidity slightly. Wall structures were mainly found to remain within the boundaries of acceptable behaviour, which could be thanks to the thermal insulation properties of wooden cladding.

'The next phase of my thesis work is to dive deeper into the significance of frontage thermal insulation to a structure's moisture performance,' Viljanen says.

The award-winning article found that the greatest challenges to the functioning of ventilation cavities are in roof structures. Roof structures have better thermal insulation than external walls, which combines with external heat transfer by radiation to keep roof structures' ventilation cavities cool during cold seasons. These effects slightly increase the relative humidity of ventilation cavities, which can hinder their performance when factoring in e.g. the structure's built-in moisture. Follow-up research will thus also consider possibilities for improving the thermal and moisture performance of roof structures.