The ideal conditions for ice dams are lots of snow and not too cold of temperatures. It needs to be below freezing to form, but the colder it gets the slower the ice dams form. What happens is that the outside edge of the roof is cold, either due to an over hang or just the fact that it is more exposed to the outside air temperature. The snow further up the roof is melted due to some source of heat. Not a big surprise since right below this portion of the roof we like to keep our homes at a livable temperature. This water flows down the path of least resistance and when it hits the edge of the roof, it freezes. Over the period of a couple of hours, days or weeks this melting snow starts to build up to eventually form the ice dams. Dam is a perfect word for it since it ends up big enough to stop the water entirely. Shingles are designed to protect against water flowing down the roof. The ice dam which just formed is essentially puddling the water behind it and pushing it back up the roof. That’s where the problems begin.

Since the ice dams form from melting snow on the roof when the temperatures are below freezing we need to discuss how the heat is transferred to the roof. We will start with a discussion on the three methods of heat transfer: convection, conductance, and radiation.

Convection is generally considered the most effective form of heat transfer. This is when air is allowed to flow freely from inside the house to the attic. In your home, it can occur if there are air leaks into the attic or any cavity that is exposed to the roof deck. The solution to this is to seal up any cracks, hatches, electric outlets or other methods of air flow. The attic is separate from the heated area, so most air flow is stopped, but even a little bit of flow can mean big heat loss to the attic and roof.

Conductance is the next most effective form of heat transfer. This occurs when heat is allowed to flow through materials such as plaster, sheetrock, metal, wood, and insulation. All materials allow some amount of heat to flow through. Metals allow the most heat to be transferred and insulation is designed to allow the least amount of heat transfer. Your best bet to combat conductive heat transfer is to add more, or better, insulation. Sometimes other things in the attic conduct heat. That might include heating ducts or plumbing stacks. These may need some added insulation around them as well.

Radiant heat flow is the least effective. When you’re talking about heat from your home, it is not a big factor, compared to the other two. However, where radiant heat is a problem is when the snow is not distributed evenly over the house. If some of the roofing is exposed on a sunny day, its darker color will absorb more heat from the sun and melt the snow that way. This is usually caused by the elements and there is little to do to directly protect against.

So when it comes to stopping ice dams from being a problem, the solutions are what are referred to as the big three: venting, insulating and waterproofing.

Venting keeps the attic close to the outside air temperature. What this does is keep the snow from melting at times when the temperature is a few degrees below freezing. If the snow is not allowed to melt and flow down to the edge to freeze again, we have prevented the ice dam from forming. This is effective because it uses convection, the most effective form of heat flow, to keep the attic close to the outside air temperature.

Insulating keeps the heat from passing through the building materials. Currently, spray foam insulation is considered the best insulation. There are two main reasons for that. First, for its thickness it out performs other materials. Second, when installed, it forms an airtight seal, stopping almost all air from getting into the attic. There are still many advantages to going with other types of insulation such as fiberglass. In fact, many people spray a couple inches of foam and cover it with an appropriate amount of fiberglass insulation. Foam options can be costly, however, just adding some insulation to your home may help prevent ice dams.

If your roof was redone it the last 20 years, or so, you probably have some form of ice specific waterproofing. This is typically in the form of a membrane which is laid down along the outside edge of your home and up the valleys. This membrane is meant to glue itself to the decking and around each nail that is put through it. It does a good job at stopping water, even if ice dams form. But as many with ice dams can attest to, it is not perfect.

Ice dams form during specific winter conditions and are not completely preventable. To mitigate the potential negative outcomes, contact Les Jones Roofing to discuss your options. We’re here to help.

Les Jones Roofing

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Les Jones Roofing

952-881-2241(O)