Large daily temperature fluctuations above and below 32° F can be very stressful to roofing systems, especially when accompanied by heavy snow or ice buildup. Roof surfaces with southern exposures that see daytime warming from the sun are particularly vulnerable. The water from daytime snow and ice melt is absorbed by some roofing material (especially concrete and wood), and then refreezes during colder night temperatures. Water expands about 9% when it freezes, creating stresses within each roofing piece and  where ice damming occurs, pooled water can back up under the roof covering and underlayment, causing leaks, or refreezing to evidentially loosen fasteners and/or even fracture rigid roofing materials especially those containing a composite of various differing materials. This ongoing movement of materials and components relative to the roof deck and house structure will contribute to a shortened roof life.

        Roofing materials vary in their ability to retain snow without large scale and sudden release on to cars, shrubs and people below, so care should be taken in using roofing materials (like metal) with poor insulating qualities on more steeply sloped roofs, unless snow/ice stops or baffles are installed.

        In extreme snow areas it can be necessary to shovel the roof to loosen and/or remove snow and ice during the winter months.

       New home designers address these concerns by complying with local building codes  that specify expected snow loads for specific locations. The primary concern is to have roofing, framing and foundation components that will withstand the total weight of the intended roofing material plus the added weight of snow and/or ice. Therefore, for new construction, as long as the specified roof (or a lighter one) is installed, there should be no danger of overloading the building structure.

       The same considerations prevail for reroofing, as long as the existing roof covering material weight is not exceeded. Care should be taken, however, if a heavier than original weight material is considered (i.e., replacing cedar/wood with concrete).  Additionally, some older homes have more than one layer of existing roofing, adding to concerns for the use of heavy materials or necessitating the removal of the existing roof (generally an excellent idea anyway).  View a summary of roofing material weights.