Michael Choffin
01-10-2014, 04:45 PM
I have recently completed an inspection on a two-story home with a mansard roof. The mansard is on the front of the house and extends to the floor line of the second-floor. During my inspection, the house had ice dams on the roof, mostly on the mansard section.
The attic is well insulation (six-inch blown cellulose and un-faced batts placed over the blown at a 90% angle); however, the attic has the furnace/A/C unit that provides conditioned air to the second floor. I’m assuming that heat radiating from the furnace, is part of the ice dam problem. The ducts (also in the attic) are circular sheet metal with insulated flexible duct as the outer sleeve. The ducts may be leaking, raising the temperature within the attic.
Since it’s a mansard, the front of the roofing system has no soffits; hence, no place to install vents to ventilate the attic area on that side. Since there are not vents, the insulation has been pushed to the edge of the attic. There is light black discoloration on the underside of the roof deck about four feet up from edge (mansard side).
I understand how the ice dams form. The attic HVAC unit and ducts probably contribute to the problem with heat radiation. The lack of ventilation through the mansard side probably also contributes to the issue.
Would it help if rigid insulation was applied to the roof deck on the mansard side ? The insulation would “shield” the deck from the “warm” attic air and radiation from the furnace.
The attic is well insulation (six-inch blown cellulose and un-faced batts placed over the blown at a 90% angle); however, the attic has the furnace/A/C unit that provides conditioned air to the second floor. I’m assuming that heat radiating from the furnace, is part of the ice dam problem. The ducts (also in the attic) are circular sheet metal with insulated flexible duct as the outer sleeve. The ducts may be leaking, raising the temperature within the attic.
Since it’s a mansard, the front of the roofing system has no soffits; hence, no place to install vents to ventilate the attic area on that side. Since there are not vents, the insulation has been pushed to the edge of the attic. There is light black discoloration on the underside of the roof deck about four feet up from edge (mansard side).
I understand how the ice dams form. The attic HVAC unit and ducts probably contribute to the problem with heat radiation. The lack of ventilation through the mansard side probably also contributes to the issue.
Would it help if rigid insulation was applied to the roof deck on the mansard side ? The insulation would “shield” the deck from the “warm” attic air and radiation from the furnace.