Hygrothermal performance of cold ventilated attics above different horizontal ceiling constructions – Field survey

To save energy ceilings towards a ventilated cold attic space are normally insulated. In Denmark the insulation
material thickness and type varies but the common used insulation material type is mineral wool or cellulosebased
insulation. Furthermore, some attics have vapour barriers, whereas others do not or only have poorly
sealed vapour barriers. The effect of these variations on the humidity conditions in cold ventilated attics was
investigated in preparation for evaluating the existing recommendations on when and how to add additional
insulation to ventilated attics to reduce energy consumption. The investigation has been done by examining and
measuring the relative humidity and temperature for at least one year in 34 attics in inhabited single-family
houses. In addition, outdoor and indoor temperatures and relative humidity were measured. The results were
divided into different groups based on the vapour barrier type, amount of insulation, and insulation material
type. Most of the attics were ventilated according to the Danish recommendations. Contrary to the expectations,
the thickness of insulation material had no effect on the temperature or relative humidity in the attic. The type of
insulation material or the presence of a vapour barrier also did not have any noticeable effect. Apparently, the air
change rate (ACH) is more important than the investigated parameters. Combined with previously published
results from controlled full-scale experiments, the results from this study are valuable input to new recommendations
on how to apply additional insulation in existing ventilated attics