Ice Dams are caused by irregular melting of snow from the rooftop. “Hotspots” as they are called, cause fast melting in some areas on a roof. These melting spots cause a water flow to the edge of the roof. Like a bridge freezes before a roadway, the runoff refreezes in a blockage over the eave of the roof. It would seem that a flat area on the edge of a roof would aggravate such an occurrence, however the cause of the ice dam should be the object of discussion and not the result.
Hotspots cause the ice dams. The answer for an asphalt shingled roof is to ensure proper intake and exhaust ventilation. Asphalt roofs readily transfer heat through the roof and in the winter, the hotspots result from this heat transfer from the interior of attic. Another cause is the rapid heating of areas from the sun. As soon as a given area is exposed from interior heat melt, the sun causes the rapid melting in some hotspots. The above description is true for asphalt shingle roofs.
Hotspots do not occur in the same concentrated way they do on asphalt rooftops. Slate by comparison, is much thicker and resistant to immediate heat transfer. Slate systems can be compared to asphalt systems in an analogy that compares frying pans on a small stove burner. If a thin metal pan is over heated on a small burner, the result will be a burn directly over the burner below. A heavy cast iron pan however, placed over the same burner will heat in a more uniform fashion, transferring heat to the outer edges of the heavy pan. Slate roofs are like heavy cast iron skillets and they transfer heat slowly. It is more rare to find a damaging ice dam on a well serviced slate roof in the Delaware Valley. Slate roofs do not contribute to the rapid heating of snow as do the Asphalt roofs.
A damaging ice dam over a Yankee Gutter is usually the result of the replacement of a natural roof with an Asphalt roof. This mix can cause trouble. The old systems that are restored properly usually perform well through all weather conditions. So it is to the credit of the old world craftsmen that knew what worked and employed sensible systems. Newer methods are a strange mix of products pushed into the marketplace and the modern thinking based upon new age construction methods. Old home have their special needs and staying with proven systems provides true return on investment.
The Yankee Gutter is a puzzling thing to many who look upon it. Many of these systems have been retrofitted with new linings, such as rubber and modified bitumen, but these systems were originally designed for metal linings. It is not a rare occurrence to see a center spout added because the old Yankee Gutter has sagged in the middle. The wood often is not rotting and some can be salvaged in a Yankee Gutter rebuild. The nails often will rust on poorly maintained Yankee Gutters. The nails begin the give way and the structure of the Yankee Gutter sags. In this scenario, the entire area that is sagging has to be removed and reconstructed. Most Yankee Gutters have an interior grade that maintains the slope of the gutter, while the soffit and cornice below is for show. Many Yankee Gutters have supports below that are either faux or functional. The difference can usually be observed in the size and style of the details. Brackets are usually larger on the vertical than twelve inches. Dentil Blocks & Corbels are used under these eaves for appearance and sometimes for structure. Sometimes the details must be reconstructed. The cause of the failure of these systems, like the cause of ice dams from above, is often the the shoddy repairs with new age products like asphalt tar, rubber linings, and quick fix methods that do not work. Once a Yankee has sagged, it is doomed and the home may suffer structural damage from continued neglect. |
