Building Leaks: Not Always the Obvious
You might not have any claims dealing with ice damming on your desk right now. However, winter will be here before we know it.
Ice dams are often the cause of costly damage to roofing systems and interior finishes, particularly in mountain environments. Even when ice dams are thought to be the obvious cause of damage, it is worthwhile to investigate other less obvious factors that may be contributing to building damage.
When dealing with claims involving ice dams, first make sure you have a fundamental understanding of them. There are many variables affecting ice dam formation, so we will only cover the basics.
Ice dams form when snow on a roof melts and later refreezes. The melting is caused by heat from the building, ambient temperature or solar heat. These factors may work alone or in combination. The melted snow refreezes when it reaches the cold roof eave or drip edge and/or when the temperature or solar heat suddenly decreases (such as at nighttime in the mountains). This process repeats itself, and the ice dam will grow larger. Water from the ice dam may back up underneath roofing materials and cause costly damage from roof leaks. The illustration shows an example of a typical ice dam.
If ice dams are present, it is easy to presume they are the cause of roof leaks or other damage. While this is often the case, you may want to investigate other factors.
We recently investigated a log home in the mountains that had interior water stains. Ice dams were present on the home, and they were thought to be the cause of the damage. Our initial investigation included an assessment of the damage, noting locations of the water stains as well as roofing damaged by ice dam removal.
The damaged roofing provided insight by exposing ice and water membrane that had been placed underneath the roofing. Ice and water membrane provides a waterproof seal (even sealing itself around nails driven through it). This meant that any water backed up from ice dams could not have caused the interior water stains. Further, some of the water stains were located at the gable end walls, where ice damming would not have occurred.
No vapor retarder had been installed between the warm living areas and the cold attic. In addition, the spaces where the walls meet the roof eaves and floor lacked adequate insulation. Consequently, humidity (normal amounts that occur in any occupied home) could migrate to and freeze in the walls or attic. In warm weather, this moisture melted, causing the water staining.
Since no vapor retarder was installed and insulation was inadequate in some areas, the water stains were the fault of either insufficient design, poor construction or both. A vapor retarder installed in combination with proper venting and insulation would have greatly reduced the amount of moisture migrating to the attic and walls and prevented the water stains. Although the ice dams were not to blame in this case, proper venting would also reduce them and potential liability from falling ice.