Photo: DTU Civil Engineering

We need to understand the air humidity in cold attics better

Monday 07 Mar 16
Increased insulation of our homes is linked to a higher risk of mold and other moisture damage in the attic. On this basis, DTU Civil Engineering presents results from a two-year long study that questions whether cold attics facing north are actually fit for the Danish climate.

Increased insulation of our homes means cold attics get even colder. Leakages in vapour barriers that insulate the houses result in warm, moist air getting into the cold attic where it condenses and thus creates moisture. This condensation creates a breeding ground for mould growth and other moisture related problems.

In 2012 researchers from DTU Civil Engineering wondered if the increased use of insulation in our apartment buildings has made attics more susceptible to mould and moisture problems than before.

In cooperation with Byg-Erfa and with funding from The Landowners' Investment Foundation the researchers conducted an experiment where they equipped a 12 meter long container with eight different types of attics. Some of the rooms were designed with ventilation, some with pressure compensation, while others had no pressure equalization or ventilation.

Surprising results gave rise to a new trial stage

"In the study we made some artificial, controlled leakages in the vapour barrier, so that air could rise up to the attics. The experiment ran for 14 months, and when we had collected our data, we opened the attics from outside. We were very surprised to see that the room that followed our usual building style – the ventilated room – was the one where we found the most mould," explains Søren Peter Bjarløv, Associate Professor at DTU Civil Engineering’s Section for Building Design.

The results from the trial surprised the researchers so much that they decided to launch a second phase of the project, where they examined several variations of insulated attics. This stage is still ongoing and will be completed in early 2017 and is also funded by The Landowners' Investment Foundation.

"Overall the measurement results, at least indirectly, questioned whether cold, north-facing and well-insulated attics actually are fit for the Danish climate. This type of attic experiences particularly high levels of relative humidity. It must be said that this type of attic represent a worst-case scenario, but they are found in Danish homes," says Hans Peter Bjarløv.

Computer simulations will provide better understanding of climate impacts

Using CFD simulations (Computational Fluid Dynamics) the research team works to examine how wind, temperature and ventilation design affects the flow conditions in the cold attics.

"We hope that the results from the simulations will show us what type of air currents that exist for a given, representative type of weather. That way we get a better understanding of why cold, north-facing attics experience such high levels of relative humidity, "explains Søren Peter Bjarløv and stresses that the conclusions are temporary. A final assessment will be made in 2017, when the final conclusions from the research in moisture in cold attics are ready.

The preliminary results of the research was presented at a symposium on February 22 at DTU.