Check what you already have
Many soffits are already vented, and some that look vented are not. From the ground, look for perforated vinyl or aluminum panels, a slotted strip down the middle of the soffit, or small round plug vents. If you see any, the question is whether they work.
The attic answers that. On a bright day, switch off the attic light and look along the eaves. Daylight at the bottom of the rafter bays means the intake is open. No light usually means insulation packed down onto the soffit, solid wood blocking between the rafter tails above the wall, or perforated panels fastened over the original solid plywood. That last one is common after re-siding: from outside it looks fully vented while letting almost no air in.
Each of those needs its own fix. New vents cut beneath a blocked airway buy nothing.
Cut-in vents, a continuous strip, or vented panels
Individual cut-in vents are what this estimate prices: louvered 16 by 4 inch vents, each screwed over an opening cut slightly smaller than its flange. They suit a sound wood or plywood soffit. Air enters at points rather than along the whole eave, so where blocking divides the soffit into separate bays, each bay needs its own vent.
Continuous strip vent runs the full length of the eave. Two parallel saw cuts remove a narrow band of soffit board and a slotted aluminum strip covers the gap. It gives more open area per foot than spaced vents and feeds every rafter bay, which is why it is the usual partner for a ridge vent. It is priced by the linear foot, so it does not map onto the vent count in this calculator.
Fully vented soffit panels replace the soffit covering altogether. That is soffit replacement, as is a new wood soffit: usually a siding or carpentry job priced per foot of eave, and the right call when the existing wood is rotten. Any solid board left behind new panels has to be cut out or vented, or the perforations vent nothing.
Half the job is inside the attic
A soffit vent only lets air into the eave. To do any good the air has to slip over the top of the wall, run up the underside of the roof deck and leave at the ridge. On many houses insulation fills exactly that gap, because it was blown right out to where the rafters come down onto the wall.
Baffles, also sold as rafter vents or vent chutes, keep that path open. Each is a foam, plastic or cardboard channel stapled to the underside of the deck in one rafter bay, running from above the soffit to past the top of the insulation. Insulation sits under it and air runs over it. The estimate allows an hour for pulling insulation back, but baffles are not a priced line, and fitting one in every bay of a low-pitched roof means working on your stomach in the tightest corner of the attic. Expect a separate price if the eaves are packed.
Solid blocking between the rafter tails has to be drilled through, or swapped for screened vent blocks, before a vent below it will draw. That carpentry is a common reason two quotes for the same number of vents land far apart.
How many vents, and why it depends on the roof vents
Intake is sized against exhaust, not on its own. The building code, IRC R806.2, asks for 1 sq ft of net free ventilating area per 150 sq ft of attic floor, reducible to 1 per 300 under certain conditions. Normal practice splits that between soffit intake and high exhaust, with intake at least equal to exhaust. Net free area is what is left open after the louvers and screen, far less than the size of the vent face, so count from the figure printed on the packaging. The roof ventilation calculator turns your attic floor area into a soffit vent count.
Too little intake is the more harmful mistake. A ridge vent or attic fan that cannot draw from the soffits pulls air up from the house instead, through ceiling light fittings and the attic hatch, carrying moisture onto the cold underside of the deck. If a roofer proposes more exhaust without asking about your soffits, ask why. Types of roof vents covers how each exhaust vent pairs with soffit intake.
What the price covers, and what a quote should show
The estimate covers 20 vents, galvanized screws, a tube of sealant and 6 person-hours at a $72 hourly crew rate. That labor, $367 to $497, is the larger share because every vent means moving the ladder, marking against the rafter bays, cutting overhead and fastening with the louvers facing the right way.
Not included: baffles, opening up blocking, painting, second-story eaves that need more than a ladder, and repairs to soft wood found at the cut. Rot in a soffit usually means water getting in from an overflowing gutter or missing drip edge, which is worth fixing first.
A useful quote names the vent and its net free area, gives the count and positions, says whether the attic side will be checked and cleared, and mentions the exhaust the vents are meant to feed. A bare vent count with no word about the attic prices only the cutting.