Unvented attics in old houses
Attic ventilation as we understand it: intake at the eaves, exhaust at the ridge, balanced so air moves continuously, is a relatively modern idea. Most of the housing in this region predates it, and a great deal of the rest got the minimum a builder could install. In a climate with hot, humid summers, the covering pays for that.
- 1 Ridge caps. Thin, fully exposed, and usually the first course to let go.
- 2 The field. Slate on the older rows, shingle on the rest, each on its own clock.
- 3 Valleys. Two slopes emptying through one line, with litter holding the water there.
- 4 Flashing. Old masonry, and the party wall a rowhouse shares with the house next door.
- 5 The vent boot. A small rubber part with a far shorter life than the roof it sits in.
- 6 Eaves. Where the porch roof ties into the wall, and where backed-up water gets in.
What an unvented attic does to a roof
Trapped heat cooks the shingles from underneath through four months a year, accelerating exactly the aging that the sun is causing from above. It also drives up cooling costs, which is how many homeowners discover the problem without connecting it to the roof. In winter the same lack of airflow lets household moisture condense on the underside of the sheathing, which shows up as staining, rusted nail tips or damp insulation long before it becomes a visible ceiling problem.
On the older stock here the causes are specific and findable: no soffit intake because the eaves were never built with any, insulation blown in over whatever intake existed, bath fans ducted into the attic rather than outside, and finished third floors that removed the attic space altogether.
Replacement day is the cheap moment
Correcting ventilation as a standalone project means working around a finished roof. Correcting it while the deck is open costs a fraction: intake vents cut in, ridge exhaust sized to match, baffles that keep the path clear of insulation, fans ducted properly.
On a house that never had any of it, this is the difference between a new covering reaching its rated life and repeating the last one. Make it an explicit line in the quote: “we reinstall the existing vents” is not a ventilation scope, particularly on a house that had none to begin with.