A ridge vent with nothing feeding it
A ridge vent is the easiest upgrade to sell during a re-roof, and on a great many houses here it was added to a roof that has no way to let air in. A vent with nothing feeding it does not do nothing. It does something worse.
- 1 The ridge. One ridge over two households, and one of them pays to replace it.
- 2 The field. The part everyone looks at, and rarely the part that actually failed.
- 3 Valleys. Most of them were cut in later, when the house was divided into flats.
- 4 The chimney. Often two of them, and often neither one carries anything any more.
- 5 Penetrations. Two kitchens and two bathrooms mean twice the holes on the same roof.
- 6 The overhang. Where heat from a flat you do not control comes back down as ice.
Ventilation is a pair, not a part
Air has to enter low and leave high. The intake is at the soffit, along the eave; the exhaust is at the ridge. Remove either one and the system does not half-work, it stops working.
On this housing the intake is the half that is usually missing. Many of these houses were built with closed soffits and no vents at all, and on the ones that had them, insulation blown in later has buried them.
What an unfed ridge vent actually does
Air still leaves through it, because warm air rises and the opening is there. It simply comes from somewhere else — through every gap between the living space and the attic: the hatch, the light fixtures, the plumbing chases, the top of the partition walls.
So the vent pulls heated indoor air up into the roof, which is precisely the condition that makes ice at the eaves. The upgrade sold to protect the roof is feeding the problem it was meant to prevent.
How to check, and what to ask
From the ground, look along the underside of the overhang. Continuous perforated soffit or individual vents mean intake exists, at least in principle. A solid painted board means it does not.
From inside, look where the roof meets the outside wall at the eave. If insulation is packed tight into that corner, the intake is blocked even if the vents are there.
And in the quote: is intake being added or cleared, and is the exhaust sized to match it? A quote that lists a ridge vent and says nothing about the soffit has named half a system.