Melting and freezing of snow on older townhouses

Paper in proceeding, 2011

The snowy winter 2009/2010 caused many newspaper articles on icicles from buildings and the risk for people walking below. The problem starts with snow melting on the roof from heat loss from the building. This melting water will run down the roof and part of it will freeze on the overhang. The rest of the water will either run off or freeze in gutters and downpipes or give icicles. The paper describes a model for the melting and freezing of snow on the roof. Important parameters are roof length, overhang length, heat resistance of roof and overhang, outdoor and indoor temperature, snow thickness and thermal conductivity. If the snow thickness is above a limit value (snow melting limit) part of the snow will melt. Another interesting limit value is the dripping limit. All the melting water will freeze on the overhang, if the snow thickness is between the two limit values. Only if the snow thickness is above the dripping limit will we get icicles. The model is used on an old town house without much thermal insulation and compared with newer townhouses. A discussion on attic temperatures is included. The results show that better thermal insulation or ventilation with outdoor air is the best way to reduce the risk for icicles.