I recently purchased a 1910 Victorian in Montana. The house is brick on a granite block foundation with a full semi-finished basement with garage under the house. The walls are mostly lathe and plaster on the first floor, which is 90% original.
The house is heated with gas-fired water radiators and provides excellent heat. The house sits with full southern exposure on one side and great east and west exposure in the front and back.
Recently we've had a week of very low temperatures (-20s) with it only getting to 0 or the teens during the day (don't worry, I'm an East Coaster and this weather is great. Yesterday it was 16 and I was doing yard work in a t-shirt. Back east I'd freeze to near-death at 40 degres!)
Coming with that I ended up with ice dams in one of the new additions to the home. On the second floor what was formerly the attic has been expanded with new gable roof and drywall on the inside. There is still the "old" attic area as well as the two new gable attic areas that increased the living space. The entire attic is very well insulated. All the new additional areas have been corebonded with insulation at the lover levels. There is 12" to 16" of blown in insulation on the attic floor.
Yesterday water was leaking down to the living space on the second floor. I went into the attic and noticed the entire inside of the roof structure was wet and dripping. I did my research and discovered it was due to ice dams. A contractor came over and went through the attic with me and confirmed the attic is well insulated. Too well insulated it seems as it is air tight and there is no air flow.
There is a ridgeline vent that is in good condition and is not blocked.
However there are no soffit vents and they likely could not be installed. The areas where they would need to be installed are blocked by the corebond. It would require a major reworking to get them installed in there.
Short of soffit vents are there other options? One of the new gable additions faces East. The second one (and the one with the major leak problem) faces South.
The attic is very warm - liveable warm. It's not flowing from below due to the great insulation on the attic floor and the fact that the builders added 5/8" thick drywall on the 2d floor ceilings. All seams and joints from the 2d floor to the attic are either covered in insulation or have been sealed with that yellow spray stuff. Heat transfer from the 2d floor to the attic is minimal at best.
The heat is coming from the full southern exposure. 70% of the roof area gets full sun. 30% is on the back half and is the older part of the house that does not have the new addition. No ice dam problems there that I'm aware of.
So long post and short question:
Will gable vents help the situation at all? The contractor who came by is looking into some options for me. The two additions that were built have cedar shakes on the sides of them. The roof is newish and asphalt.
We are thinking that a gable vent on the east side and then one on the southern side would help with air flow. Right now there is none. I ensured the ridge line vent was free and clear along its entire length but there is no fresh air coming in from anywhere.
ETA: the roof pitch is very steep. There are overhangs extending past the heated living areas that are about 1' to 1.5"
I tried to attach a photo but am getting an error that it isn't a valid image file, even though it is.