Ice Dams with New Construction
So, first bit of snow and cold weather (St Paul, MN) and we’ve ice dams. Our house is nearly complete – rocked and primed, most cabinetry and trim installed. Photos: https://www.instagram.com/bamasotan/
The 3rd level (attic) is finished and conditioned. The crawl spaces behind the knee walls are conditions (insulation is against the underside of the roof deck from eve to peak). All HVAC ducting in upper levels is within the insulation envelope. House is currently kept at about 60°f.
Blower door after insulation & prior to sheetrock is 1.8 @ ACH50. (Initial was 4.6 and then they went through finding leaks and said that 1.8 was the best they could do).
Walls – 3″ Closed cell foam + blown fiberglass to fill out the cavity.
Roof – 7″ (R-49) closed cell foam. Some bays are vented (durovent), some are not (hot roof). Roof is mostly truss, some solid rafters then sheathing then cedar shingles directly on sheathing (numerous MN builders have stopped using cedar breather saying that they’ve seen no difference when it is or is not used which I’m guessing is because it doesn’t provide nearly enough air flow to be effective).
Lower edges of roof do have Grace I&W.
Ice dams are on both east and west sides of house. I need to get a drone up to see south and north facing roof segments. About 95+% of other homes in the area are free of ice dams so far this year so our having them is somewhat unusual.
Possible causes? Solutions?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part