Ice Dams
December 21 2020 Case Study Residential
Several factors contributed to problem roofing area in the photo below. Even though the shingles were in good condition and installed properly, leaks were occurring in the winter months due to ice dams. To remedy the situation, the homeowner installed an electrical device called snow and ice melting cables.
Snow and ice melting cables are not recommended in the Cincinnati/Northern Kentucky area for the following reasons:
1. Electrical Cables do not prevent an ice dam from occurring. They are a reactive measure that does not address the cause of the ice dam formation, usually an inefficient attic insulation system.
2. They are not energy efficient. A poor attic insulation system (or thermal boundary) allows heat to escape into the unheated attic space, increasing a homeowner’s gas and electric usage. Installing heating cables will further increase the energy usage while attic insulation will decrease usage and eliminate the ice dam.
3. Ice melting cables are dangerous to install on a roof covered with ice and can be a fire hazard.
Most ice dam formations are easy to eliminate by insulating the attic space to R-49. The illustration below shows what happens when melting snow above heated areas of the roof reach the cooler (unheated) roof sections. It is worth noting than the outside temperature must be below freezing for an ice dam to form.
The cause of ice dams are sometimes a little more difficult to pinpoint and can occur on homes that appear to be well insulated and ventilated. The following conditions can also cause ice dams in the Cincinnati/Northern Kentucky area:
1. Displaced insulation from other Contractors
2. Inefficient Ductwork causing hot air to leak into attic space
3. Bathroom vent improperly installed, allowing hot air into attic space
4. Cathedral Ceilings
5. Large roof areas emptying into a small gutter
6. Solariums or Three Season Rooms
Displaced Insulation
An ice dam was occurring in this home shortly after another contractor installed two new speakers in the attic. After an inspection of the roof system of this home (pictured below), displaced insulation was found to be the cause of the heat loss/ice dam. More insulation was evenly applied and the ice dam was eliminated.
A new cable connection was installed in the attic pictured below. The contractor did a poor job cleaning up and left failed to reinstall much of the attic insulation. As a result, the heat loss caused an ice dam. The end result included drywall and gutter damage. This could have been avoided if the thermal boundary was not compromised.
Inefficient Duct Work
The ice dam in this home was not caused by inefficient attic insulation but by leaking duct work. Ducts that are located within a roof system must be air tight. Two problems occur when hot air escapes into a cold attic space – Ice Dams and Condensation. Good attic ventilation can minimize the negative effects of leaking duct work as it relates to ice dams but the ducts should be inspected and repaired. A furnace pumping hot air into the attic space will warm the attic and cause an ice dam. Attic temperatures need to be within 10% of the exterior temperature during the winter months. If this is achieved it is improbable that an ice dam will occur. (Condensation is discussed in other areas of our website.)
Bathroom Vent causing Ice Dam/Condensation
Bathroom vents that exhaust directly into an attic space can cause ice dams and Condensation when they introduce warm moist air into a cold attic. Problems are magnified when improperly installed bathroom exhaust fans are left running for long periods of time, dumping heated interior air into the attic. Bathroom Exhaust fans should always be vented to the exterior of the house and not into the attic. The best way exhaust them is through the roof with a louver. The illustration above shows the proper way to install a bathroom exhaust system.
Cathedral Ceilings
Cathedral ceilings are known for their charm and beauty to most homeowners. However, if they are not properly designed, they can cause problems such as ice dams and energy loss. Cathedral ceilings need to be constructed with 2″ x 12″ rafters in order to achieve a minimum of R-30 insulation. When they are framed with smaller 2″ x 6″ rafters the amount of insulation that can be properly installed between the drywall and roof sheathing decreases to R-19. Batt Insulation installed over cathedral ceilings often contains an opening that allows heat to escape. Ice and Water shield should always be installed on roofs with cathedral ceilings as a preventative measure.
Large Roof Areas emptying into a Small Gutter
Even roof systems with good attic insulation will allow some heat to escape the interior living spaces. When a large roof area drains into a small gutter, problems can occur. These problems are minimized when melting snow and ice drains into a larger (longer) gutter. Ice and water shield should always be installed in these problem areas to prevent interior leakage.
Solariums or Three Season Rooms
The photos above are from an unheated solarium with no attic insulation. This room was not designed for use in the winter months. A SPACE HEATER was used by the homeowner to make the solarium more comfortable during the winter. Heat is able to escape when the space heater is in use since there was no attic insulation installed. The homeowner experienced an ice dam when the melted snow reached the overhang (as seen by the stains on the exterior siding). Attic insulation was added to the solarium to eliminate the heat loss and the resulting ice dam formation.
