Effective Ice Dam Prevention: Two-Family Residence
The conversion of a church into two side-by-side townhouses was done with little regard for heat loss into the attics. The level of insulation on the attic floor provided about an R-15 at best. The result was significant heat transfer through the attic floor-plane that caused rapid snow melt and subsequent ice dams. Adequate ventilation existed and met code requirements, but needed to be complimented with a sound thermal (and air) boundary between the attic and conditioned space below in order to help prevent snow melt.
Energy Egghead air-sealed the attic floor and applied cellulose insulation to provide an R-value of 60. Brick walls with an original plaster & lathe interior made it impossible to insulate the sides of the building without gutting the interior. Thus, adding extra R-value in the attic made economic sense in addition to stopping ice dams and making the occupants more comfortable.
The picture above shows no icicles over the properly insulated attic on the left, while on the right side, the townhouse without proper attic insulation shows ice dams. Energy Egghead later performed the same sealing and insulation on the right townhouse.