Ice dams form after significant snowfall on the roof melts from a heat source, such as warm temperatures or heat loss from an attic and then refreezes. Melting snow runs down the roof, only to be frozen again when the sun goes down and the temperature drops.
The partially melted snow and water pools, then freeze at the eaves of the structure and an ice dam forms with the overflow forming icicles. Since heat entering the attic rises to the peak, the eaves of the structure always remain colder and the ice dam can’t melt to allow water to run off the roof. With repeated thaw-and-re-freeze cycles, the ice dam problem builds, and considerable water is trapped or pooled at the eaves or the base of valleys. While in a liquid state, the water seeps under shingles and tar paper (roofing felt) designed to protect the roof system from water intrusion. Eventually, the water seepage saturates plywood decking around the eaves and it wicks upward until large portions of the decking become water saturated.
As the damp roof decking warms up, the conditions are perfect for microbial growth to occur. Since the roof decking is usually hidden by insulation in the attic, mold growth often goes unnoticed. People may experience allergic reactions or distress depending on their sensitivity to mold. Property owners could notice water collecting on ceilings or running down interior walls causing dampness or discoloration of drywall. In other cases, water could run through wall framing and pool along the edges of or underneath floor finishes and go unnoticed.
Certainly, at the first sign of water on construction components inside the structure, it behooves property owners to conduct a thorough investigation into the source and quantity of water, and take corrective steps (extraction, drying) immediately. Since most property owners lack the expertise and metering equipment necessary to conduct a thorough investigation of moisture intrusion, it’s important to call a professional with the proper equipment that employs certified Mold or Water Restoration Technicians (WRTs). Failure to dry moist building materials can result in secondary damage, such as mold, dry rot or structural damage.
Call SteamMaster at 970-827-5555 for an InfraRed Thermal Imaging Camera Inspection today.
Source: http://www.randrmagonline.com/articles/83597-ice-dams-and-water-damage Jeff Bishop 2007