Ice dams often form on the roof following a heavy snowstorm and the onset of low temperatures. Ice dams form when the snow at the peak of the roof melts, which causes the melted water run down the slope of the roof until it refreezes as it reaches the colder surfaces at the eaves (the edges, or overhangs of the roof.) of the roof.
Ice dams can cause a very costly water damage to your roof deck, attic space, insulation, interior walls and ceilings. When an ice dam forms at the eave of your roof, it blocks off water and causes it to rise up underneath the roof shingles thereby penetrating inside your home. The water will generally rise up faster on the roofs with lower roof slope. The damage caused by ice dam built up can be very costly. You may be required to replace wet insulation, damaged dry walls and ceilings, remove mold, and replace rotten wood in your home. It is obviously, much easier, and far less costly to stop ice dams before they happen!
How do ice dams form?
Before you can prevent ice dams from forming on your roof, you need to understand the mechanism behind the ice dam formation. In the winter, your roof gets covered with snow, which is pretty normal. Ideally, this snow would eventually evaporate in the sun, as often happens in the case of roofs of abandoned homes and empty buildings.
Whenever there is snow accumulated on your roof, warm air from inside of your home rises up into the attic space. Once in the attic, the warm air continuous to rise up until it reaches the top or peak of the roof. It is then that the roof surface starts to warm up, which also starts melting of the snow on top of the roof. The water formed by the melting of the snow runs down the surface of the roof underneath the snow-pack. When the melted water reaches that colder area of the roof, it refreezes forming a wall of ice.
This wall of ice is called an ice dam. The ice dam traps melted water, and eventually, it causes the melted water to rise up underneath the shingles, which allows it to get inside your house and cause extensive water damage to your property. This damage may not be immediately apparent as water gets absorbed by insulation in your attic space, insulation in between the wall cavities, and finally, dry walls, plaster and ceilings.
The insulation that has been exposed to water gets wet and can no longer insulate your home properly. Any wet insulation needs to be replaced. The damages to dry walls, and rotten wood will also require replacing. If you do not take prompt measures, then a mold growth can occur behind your walls without you even knowing about it!
How to Stop Ice Dams
Because it is the warm air that makes its way into the attic space and causes the snow on top of the roof to melt, we need to find a way to insulate the attic space and keep it cool in order to stop ice dams from forming. The goal is to have a cool attic space with the temperature at or below 30° F.
There are two ways to keep your attic space cool; insulation, and ventilation. You will find that most older homes do not have sufficient levels of insulation. Many of the older homes do not have an adequate ventilation, either.
Attic insulation requirements
For most homes located within a snow belt zone, a minimum attic insulation level equivalent of R – 49 is required in order to provide sufficient level of installation for your home. Most homes built before the 1980s will not have sufficient levels of attic insulation, nor will they have sufficient levels of wall insulation for that matter.
Maintaining sufficient levels of insulation in your home is not only helpful for the ice dam prevention, but it is also great for attaining higher level of energy efficiency in your home. By properly insulating your home you will decrease your heating and cooling costs, which in turn will lower your home’s carbon footprint and help you save money off your utility bill.
Before you head out to buy more insulation for your attic, you will need to find out the existing / present R – value level of insulation in your attic. You will then need to measure the surface area of your attic so that you can estimate the additional level of installation required for your attic.
How to measure attic insulation
You can measure the thickness of your attic floor insulation with a simple ruler. For example, If you find that you have 8 inches of existing fiberglass blanket insulation covering your attic floor, then multiply it by 3.14 to derive its are value.
By multiplying 8 inches of fiberglass blankets times 3.14, we get approximately R – 25 value. It means that will will have to add another 7 to 8 inches of insulation to bring in up to the required R -49 insulation value.
Sealing off the air leaks in the Attic
Aside from additional insulation, you will want to identify and seal off any holes, air leaks and drafts in the attic. Once you find the air leaks, you can seal them off with caulk, spray foam, or weather stripping.
Beefing up your inadequate attic insulation
When adding any necessary extra insulation to your attic floor, you will want to make sure stay away from the the outer edges / walls of the roof because you could inadvertently cover soffit vents locates at the eaves of the roof. The soffit vents serve the function of pulling the cold a air inside your attic. You will Therefore want to keep your soffit vents uncovered. Another reason why you want to keep the insulation blankets away from the edges and interior walls of the roof in your attic, is because it actually helps to keep them warmer, which helps prevent ice dams from forming on the eaves of the roof. Not covering the very edges of the interior roof walls will also help prevent moisture from getting trapped and thereby causing condensation to form inside the attic. We do not want any of that!
If your home has the so called soffit vents (small openings underneath the overhangs of the roof) that help bring the cold air inside the attic, and the ridge vent that circulates warmer air out of the attic, then you are in good shape. If your attic does not have soffit vents, that it is likely that there are gable vents, the window like openings on both sides of the gable walls of the attic. It may be necessary to expand the size of the gable vents in order to provide sufficient levels of attic insulation. As a rule of thumb, there should be a 1 square foot of ventilation in the attic for every 150 square feet of the attic floor. You will find that most older homes do not have that, and it may therefore be necessary for you to bring up the level of attic insulation to sufficient level. Expanding the size of the gable vents may be an easy way to do it.
How Do I keep my Attic Space Cool, if I have a heating furnace installed in the attic?
If you have some sort of a heating unit or a gas furnace producing the heat in your attic, then you you will need to install power vents to rid your attic of warm air produced by heating unit. It will also be necessary to properly insulate the heating unit to reduce the amount of heat it passes into the attic space. If you choose to install a power ventilation to cool off your attic, you will also need to make sure that there is a sufficient intake of cold air from the outside. You could have a power exhaust vent installed on one side of the gable wall in your attic, while having an equally sized intake gable vent on the opposite side of the attic gable wall.
Other options for dealing with the Ice Dams
Ice Melting Cables
There are some special ice-melt cables you can install on top of the shingles at eaves of your roof. Needless to say, these special ice-melting cables will have to be properly grounded and turned on manually after a heavy snowfall. You will have to remember to turn them off once the snow clears, or they will burn out.
You can also use the snow rakes to help you get rid of the snow at the eaves of your roof after a snowstorm. Be very careful if you have to use a ladder to reach the roof. You will want to make sure that your ladder is properly placed and secured before climbing it.
Modern Standing-seam metal roofs our specially coated to help the snow fall of the roof before it has a chance to accumulate. There many metal roofs installed in the “snow country” – New Hampshire, Maine and Vermont, because metal roofing can be a great way to virtually eliminate ice dams from forming on your roof in the first place. Be extra careful if you want to use snow rakes to remove the snow from your metal roof. There is a high chance of scratching and damaging the paint finish of your metal roof.