Todd Miller - Roofing Expert

Snow, Ice Dams, and Metal Roofing

I was looking recently at my website statistics and one thing popped up clearly – folks are really searching for information on roof ice dams and also metal roofing as a possible solution to ice damming. This has been a tough winter with snow and ice in areas of the country that do not normally get snow and ice. This poses a unique problem because, while there are ways to help make a home be resistant to ice damming, if you do not normally get much ice and snow, you don’t build your home to handle it well. Of course, oftentimes weather patterns repeat themselves for a few years so the folks getting ice and snow this year can quite possibly expect it in future years as well.
So, let’s take a look at ice damming on roofs …

There are two primary reasons why ice damming occurs on roofs. They are as follows:

  1. Heat from inside the house escapes into the attic and then reaches the roof, causing “hot spots” that melt the snow. This melted snow then runs down the roof until it hits cold areas of the roof at the eave overhangs where it re-freezes. This leads to a gradual build-up of ice on the bottom edges of the roof. This situation is most prevalent when outside temperatures stay cold and there is no sun to cause melting over the entire roof rather than just the aforementioned “hot spots”. This phenomenon, of course, describes winter in many areas.
  2. Converging snowloads on the roof, often at valleys in the roof, cause “packing” where the snow cannot slide off the roof. Eventually as this snow packs tighter and tighter, ice is formed.

When analyzing a problem, I always like to first look at what can be done to permanently fix the situation rather than just try to relieve the symptoms. So, in the two above scenarios, what is a permanent fix? Read on!

  1. Eliminating “hot spots” on a roof which lead to ice dams is best done by increasing insulation on the attic floor and also increasing ventilation in the attic. Insulation helps hold heat inside the home where you want it. Ventilation helps keep the attic as cold as possible. To avoid ice dams, ideally, you’d like your attic to be the same temperature as outside. The key to ventilation is having good intake vents and also good exhaust vents. Intake and exhaust vents need to be well balanced in terms of the air that can flow through them. They also should be positioned in a way which continually “bathes” the entire underside of the roof deck with fresh cold air from outside, eliminating “hot spots”.The issue with all of this is that some homes really are not constructed well for ventilation. That is when building a roof over the existing roof, creating a new vented chamber, can be very wise. This is also called a “cold roof”. It is not a cheap or easy fix but it is a very good, permanent fix. A product like Green American Home’s ThermaDeck can help make this method be even more effective by combining ventilation with insulation and reflectivity.A true bonus of increasing home insulation and ventilation is that these things also help reduce air conditioning loads in the summer. So, particularly for homeowners in temperate climates, these solutions to ice dams can help reduce summer energy costs as well.
  2. If ice dams are being caused by roof geometry (“shape” or “footprint”) and the resulting converging snow masses, it is difficult to arrive at a permanent fix shy of major changes to the home’s design. In this case, adding things like snowguards on the roof, uphill a bit from the trouble areas, can help hold snow and prevent it from sliding so quickly. If you can hold the snowload until it melts naturally, then you can avoid the converging snowloads and the resulting ice dams.

The next question then becomes, what if these permanent fixes cannot be made or, in the case of roof shape, do not have adequate effect? In that case, there are systems which can be added to your roof that will help in melting unavoidable ice dams. Some of these systems lay on top of the roof, such as “heat tape” and are easily added to any existing roof. Other systems become more permanent and integral to the structure and actually are placed under the roof system or under the roof deck in the areas where ice dams occur, heating the roof surface and preventing the ice creation and accumulation.

The next question that folks ask a lot of times is whether metal roofing avoids ice dams. Companies like Classic Metal Roofing Systems and Kassel & Irons produce attractive residential metal roofing systems and sometimes make the claim that their systems can help minimize ice dams. The fact is, metal roofing can help but it is by no means a cure-all for ice dams.

Metal roofs tend to shed snow more quickly than most other roofing materials. This is because they have a fairly smooth top surface and also because, when the sun does appear on winter days, heat from the sun passes through the snowload, hits the metal, and is reflected back outside. It then starts to melt the bottom of the snow on the roof over the entire roof not just over the heated areas. Once that snow melts a bit, it gets slippery and tends to slide off the roof, much like snow off of the hood of your car once the engine warms up.

However, metal roofing does not necessarily help prevent ice dams from converging snow and, if the sun doesn’t come out, snow can hang around on metal roofing for a long time just as it does on other roofing materials. So, that brings us back to not wanting to ignore the possibility of permanent solutions to ice damming even on homes where metal roofing is being installed. One benefit of metal roofing, if ice dams do occur, is that typically due to the interlocking nature of the panels, the strength of the metal, and the underlayments used beneath the metal panels, there is less chance of the melted snow and ice working their way into the homes, its walls, or its overhangs, than there can be with other roofing materials. So, even though ice dams may occur, they will be less damaging.

If you have a particularly stubborn ice dam situation, feel free to email me at Send me pictures or roof diagrams if you can including details on your home’s construction and ventilation, and I will do my best to offer solid solutions.