The Influence of Wallpaper on the Moisture Performance of Traditional Solid Walls

Wallpaper has been used for centuries to enhance the appearance of internal walls in traditional buildings. While there is evidence that wallpaper can influence the moisture performance of wall assemblies, particularly by delaying drying, limited experimental work has characterised the hygric properties of wallpaper and its role in this process. This paper investigates the vapour permeability and drying behaviour of lime plaster, wallpaper paste, and five wallpaper types to assess their impact on moisture dynamics within wall assemblies. Hygrothermal modelling using the measured material parameters is undertaken, enabling detailed analysis of moisture transport and drying behaviour across the full wall thickness. The findings indicate that the bio-based wallpaper paste and many traditional and non-woven wallpapers do not significantly affect vapour permeability or drying. However, the vinyl-coated wallpaper showed a measurable impact on moisture behaviour, reducing both vapour permeability and drying. Hygrothermal modelling shows that wallpapers with low vapour permeability (high sd value) can increase relative humidity within wall assemblies. This effect is more pronounced in walls with higher baseline moisture content, whether due to substrate properties or environmental exposure, making such walls more vulnerable to potential fabric decay.