So far this year we haven't had the extreme ice dam situation like we had last year, but it's a good idea to re-visit what an ice dam is, what you can do to prevent an ice dam, and what you can do to prevent damage from occurring to your house because of an ice dam.
What is an Ice Dam:
An ice dam is formed when melting snow on the roof is unable to flow into a gutter and down the downspout because there is ice (and/or debris) blocking the flow of the water. Here's an image that does a good job visually explaining an ice dam:
Preventing an Ice Dam:
There is no way to always 100% prevent an ice dam from forming (unless you remove your gutters), but there are some things you can do to help prevent an ice dam. The first and easiest thing to do is to make sure your gutters are clean. Either install some type of leaf protection or hire someone to clean the gutters for you a couple of times a year. For Leaf Protection, a product I really like is called Leaf Relief. It's affordable, works great, and is suitable to install into existing gutters or new gutters.
The second thing to do is to look at your attic insulation. The main cause of an ice dam is a warm roof. Warm air in your attic is heating up the snow on your roof causing it to melt, but the melting snow has nowhere to go. Attic insulation can help keep your attic and your roof cooler. You want to keep the heated portions of your house separate from your attic. The state of Maryland recommends that you have between R-39 - R-49 worth of attic insulation. Most homes have only about 6 inches of attic insulation, which equates to about R10.
Preventing Damage from an Ice Dam:
The exposure on some homes dictates that there might just not be any way to prevent an ice dam. In those cases, we need to look at how a homeowner can prevent damage from occurring to their house when there is an ice dam. There are 2 main products that Central can install that will help.
Drip Edge - A small L shaped piece of metal flashing. It slips under the last shingle above an eave on one side and then covers the lip of the gutter on the other side. Drip Edge can prevent water from backing up under the last shingle.
Ice and Water Shield - Ice and Water shield is self-adhering rubberized layer of material that is fully water proof. To prevent damage from an ice dam, I&W shield can be installed at the base of the roof along the eaves. Each roll is 3 feet wide, which will give you 3 feet of protection for standing water above your gutters.
Both Drip Edge and Ice and Water Shield are inexpensive products that are easy to install while having a new roof installed. Be sure to ask for these products the next time you get your roof replaced.