Eyebrow vents, soffit vents, and ice dams
Location: Idaho Panhandle. So ice dams are an issue.
Looking at a roof with no soffit venting, eyebrow vents and significant ice dams.
I don’t know if there is ridge vent, but there are gable vents.
My initial reaction is to recommend the install of soffit venting in each rafter bay, and baffling inside. I think the roof pitch is enough to give space to do that.
Thinking out loud, will the eyebrow vents interfere with draw through the soffit vents, providing a closer and clearer air flow source?
Kind of depends where the eyebrow vents are located.
More insulation, more venting are the enemy of ice dams.
The details matter. overhang, free space between rafters......
If anyone disagrees, please comment.
Ice Damming is caused by thawing snow which refreezes at the eaves. This occurs at the eave of a roof because the upper 2/3's portion of the roof is warm enough to allow thawing while the eave portion remains cold so the water flowing to it refreezes.
Venting keeps the whole roof cold in winter and less warm in summer.
Soffit vents are paired with ridge vents. Soffit vents create air flow to the ridge vents.
End gable vents are also in pairs to create air flow through the attic/ air space below roof and above ceiling.
Ice damming occurs when the area directly below the roof - unconditioned space - is not properly insulated - wrong or no insulation - and/ or the insulation blocks air flow between soffit vents and ridge vent.
My understanding is that adding soffit vents in your situation will not help since you have gable vents and therefore, most likely, no ridge vent. You should be able to see the ridge vent from outside if it's there.