What Those Pretty Icicles Tell You About Your Roof

Icicles tell us our house is losing heat. Warm air from living spaces finds its way into attic spaces, or through cathedral ceilings, as a result of insufficient insulation and air sealing. Recessed lights, attic hatches and chimneys are often sources of air leakage. This warm air heats up the underside of the roof and melts the snow on the roof above. The melted water migrates down the slope of the roof to a point at the eave overhang where there is no more warm air causing the formation of ice dams and icicles as the water cools and then freezes. If the ice along the roof edge is thick enough, it can force the water behind it up and under the finished roofing into attics, walls and living spaces. Roof valleys are particularly good at building up ice and potentially causing roof leaks.Often the only solution that comes to mind is to get on the roof (dangerous) and hammer out the ice dams, which will, over time, destroy the roofing materials. The bottom line is, if you have ice dams and massive icicles you don’t have a roofing problem as many assume, you have an air sealing, insulation or venting problem – or even some combination of the three. Most often the “go-to” solution is just to treat the symptom. This can be done using an aluminum or copper snow belt – the shiny metal you see applied to the first 2’-3’ of the roof eave. All the symptoms still exist but the ice will form at the metal snow belt and will simply melt and slide off once the temperature rises. This solution seems like an easy fix, but can create hazards when doors or walkways are located below.The formation of ice dams can also be addressed using heating tape that simply keeps the eave of the roof warm and allows the water to drip off instead of forming ice. It also guarantees a higher electric bill. While these solutions do not address the cause of the problem they can treat the symptoms and are often seen as the only practical solution.The other option is to address the cause, which is potentially more labor intensive but will ultimately lead to a more comfortable house and lower energy bills. In a roof with typical, non-cathedral construction, the trick is to insulate the attic floor enough so the temperature inside the attic is about the same as the outside temperature in the winter  – this means your upstairs rooms are not heating the attic space and the underside of the roof. Additionally, you will need to make sure that eave vents are open and there is clear and sufficient airflow from the eave to the ridge or gable vents. The eave area is the most difficult to ventilate and insulate properly. It requires particular attention and care to insulate this space above the exterior walls correctly without blocking the soffit vents.Cathedral ceilings and complex rooflines can present a different set of challenges. These roof designs can be difficult to vent effectively. In some cases, a non-vented roof or vented over-roof may be the best approach. Insulation can be added above the existing roofline when reroofing is involved, leaving interior details and finishes unaffected. When there is no ability to construct a conventionally vented cold attic, add airtight insulation of sufficient thickness and perhaps a small sloped venting space above it to minimize heat loss and reduce the potential for ice dams.Your roof will tell you how well your insulation and ventilation is working. If you have massive ice dams and icicles you are wasting energy, spending more money on heating than you need to, and living in a drafty, uncomfortable house. Take time to address the causes of these symptoms and call us if you would like to work on the cure.For more information, follow these links:http://www.homeenergysaver.lbl.gov/consumer/help-popup/content/~consumer~nrr~ice-dams



This image, courtesy of buildingscience.com, illustrates venting over-roof construction to allow for proper air flow, insulation and prevention of ice dams.

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