Ventilation is the part of a roofing job nobody asks about and everybody should. It costs relatively little to do correctly during a replacement and it is expensive to fix later, and it directly affects how long the roof above it lasts.
What bad ventilation does
It cooks your shingles from underneath. An under-ventilated attic in an Oklahoma July gets extraordinarily hot. That heat ages the shingles from the back side, where no warranty is looking, and a roof that should give you twenty-five years gives you fifteen.
It raises your cooling bill. A superheated attic radiates into the living space below all afternoon and evening, and your air conditioner fights it.
It puts moisture in your structure. Warm moist air from the house rises into the attic. Without a path out it condenses on the underside of the decking, and over enough winters that means damp sheathing, degraded insulation, and mold.
Balanced means intake and exhaust
This is the part that gets done wrong most often. Ventilation needs intake low, at the soffits, and exhaust high, at or near the ridge. Air enters at the eaves, moves up under the decking, and leaves at the top.
Exhaust without intake does not work. A ridge vent on a house with blocked or painted-over soffit vents cannot pull air from anywhere, so it either does nothing or pulls conditioned air out of your house. This is extremely common and homeowners almost never know.
Mixing exhaust types causes a related problem. A ridge vent combined with powered fans or box vents can short circuit, pulling air from the other opening instead of from the soffits, so the far end of the attic gets no airflow at all.
What we do
During any replacement we look at what intake actually exists, not just what is installed. Blocked soffits, insulation pushed into the eaves, and painted-over vents are all common. We size the intake and exhaust to the attic and correct the imbalance while the roof is open, which is by far the cheapest time to do it.
Common questions
How do I know if my attic is under-ventilated?+
Common signs are an attic that is brutally hot in summer, high cooling bills, rust on nails or fasteners in the attic, damp or discolored sheathing, and shingles that aged faster than they should have.
Is a ridge vent enough on its own?+
Only if there is matching intake at the soffits. A ridge vent with blocked or missing soffit intake has nowhere to pull air from and does very little. Balance is the whole point.
Should I add a powered attic fan?+
Usually not. Powered fans can depressurize the attic and pull conditioned air out of your house, which costs you money, and they can short circuit a ridge vent. Balanced passive ventilation is generally the better answer.
Can ventilation be fixed without replacing the roof?+
Some of it, yes, particularly intake at the soffits. Exhaust changes at the ridge are far cheaper to do while the roof is already open, which is why we address it during a replacement.