What is an ice dam?
An ice dam is a ridge of ice that forms at the edge of a roof and prevents melting snow (water) from draining off the roof. The water that backs up behind the dam can leak into a home and cause damage to walls, ceilings, insulation, and other areas.
What are the main factors that cause ice dams?
The main reason for having an ice dam problem is non-uniform roof surface temperature. Heat loss from a house, snow-covered roofs and outside temperatures are the perfect storm for ice dams. There are two main reasons that you could end up with an ice dam problem on your roof and they are improper attic insulation and ventilation.
If inadequate insulation is your problem, you need to make sure that it is at least R-30 (R-Value is a measure of insulation’s ability to resist heat traveling through it) attic insulation between the ceiling joists and no un-insulated gaps. Installing additional insulation on the attic floor or having insulation blow in should be top on your priority list. Also, weather-stripping attic stairways or hatchways will increase your insulation.
The value of ventilation will become apparent is there is still heat leakage in your attic after optimal insulation is added. Without adequate ventilation, heat will build up regardless of the amount of insulation. If you use the rule of thumb that you need 1 square foot of venting for every 150 feet of attic area, you will master your ventilation problem. If you live in an older home, it’s unlikely your vents are adequate. If your older home has gable vents, you may be able to replace them with larger ones to solve the problem. One of the best solutions for ventilation is adding vents in your soffits and a ridge vent. If you do this when cold air enters the soffit vents is till rise along the inside of your roof and exit through your ridge vent, it will in turn will cool your roof and remove any moisture at the same time. This will take some carpentry skills, but is not a really tough job unless you have difficulty getting to either the inside or outside of the windows.
Other sources of heat in the attic space include chimneys. Frequent use of wood stoves and fireplaces allow heat to be transferred from the chimney into the attic space. Inadequately insulated or leaky duct work in the attic space will also be a source of heat.
What causes different roof surface temperatures?
Since most ice dams form at the edge of the roof, there is obviously a heat source warming the roof elsewhere. This heat is primarily coming from the house. In rare instances solar heat gain may cause these temperature differences. Heat from your house travels to your roof surface in three ways:
- Conduction –heat energy traveling through a solid mass
- Convection –the rising heat above the solid mass
- Radiation –electromagnetic heat waves
A good example of these three ways is thinking of heating of a cast iron frying pan. The heat moves from the bottom of the pan to the handle by conduction. If you put your hand above the frying pan, you will feel the heat from it rising and that is heat transfer by convection. Heat is also transferred from the hot pan to your hand by electromagnetic waves and this is heat radiation Another example of heat radiation is when you stand outside on a bright sunny day and you feel the heat from the sun. You need to make sure that heat conduction, convection & radiation are all working properly in order to avoid having an ice dam problem.
Beware of warning signs an ice dam may be imminent?
- Large icicles hanging from your home or gutters during cold-snaps following snow storms are an indication that internal heat is melting the snow from beneath the roof deck
- You have water dripping down or ice forming on the exterior surface of your home
- Ice is developing along the overhangs of your roof or gutters
Lindus Construction / Midwest LeafGuard is a full service contractor specializing in LeafGuard Gutters, GAF Asphalt Roofing, SeasonGuard Windows/Siding/Insulation, Metal Roofing, Decking, New Construction & Home Remodeling. Call us at 1-800-873-1451 or check us out on the web at http://lindusconstruction.com. Tune into WCCO 830 every Saturday at 9am for our Home Improvement Show with Denny Long & Andy Lindus.