How do you fix roof ventilation problems you have already found?
Short answer. Match the fix to the problem: blocked or missing intake calls for opening soffits and adding baffles, mixed exhaust types call for removing all but one, too little exhaust calls for a ridge vent or more high vents, and bath fans dumping into the attic need ducts run outside. Sealing ceiling air leaks comes first in every case.
Problem: intake is blocked or missing
- Signs: insulation packed to the deck at the eaves, solid soffit, no daylight at the eaves.
- Fix: vented soffit panels, openings cut in the wood behind them, baffles in each bay. Where there is no soffit, an edge intake vent at the roof's lower edge.
Problem: mixed exhaust
- Signs: a ridge vent plus box vents, a turbine or a power fan; gable louvers open alongside a ridge vent.
- Fix: keep one exhaust type. Deck and shingle over the others, and close gable louvers from inside.
Problem: too little exhaust
- Signs: heat that lingers long after sunset, stains near the ridge, a short ridge vent.
- Fix: lengthen the ridge vent slot within the setbacks, or add box vents high on the slopes if there is no usable ridge.
Problem: moisture sources
- Signs: mold around one fan, damp insulation, rusty nails in one area.
- Fix: duct bath and kitchen fans outdoors with insulated duct and proper caps.
Problem: air leaking up from the house
- Signs: dirty insulation over top plates and fixtures, a drafty hatch.
- Fix: seal penetrations and weatherstrip the hatch before adding vents.
Timing
Intake and moisture fixes can be done anytime. Exhaust changes are cheapest during a replacement. See ridge vent vs box vents and roof ventilation basics.