A ridge vent with no intake does nothing at all.

Intake and exhaust — the whole idea in one paragraph

A roof ventilates by moving air through the attic: cool air enters low at the soffit, warms, rises, and leaves high at the ridge. It is a chimney, and like a chimney it needs an opening at both ends.

Exhaust without intake is the single most common mistake we find. A ridge vent cut into a roof with blocked or absent soffit vents has nothing to draw from, so it pulls the easiest air available — conditioned air from inside your house, through every ceiling gap. You paid to heat that air, and now it is carrying household humidity into a cold attic.

What bad ventilation actually does

It cooks the shingles from underneath

An unventilated attic in a Maryland July runs far hotter than the outside air. Shingles age from heat, and they age from both sides. This is how a thirty-year shingle becomes an eighteen-year shingle.

It causes ice dams

Warm attic air melts snow on the upper roof. The water runs down to the cold overhang, refreezes, and builds a dam that forces meltwater back up under the shingles. Ice dams are almost always a ventilation and insulation problem wearing a roofing costume.

It grows mould on the sheathing

Humid indoor air with nowhere to go condenses on cold plywood. Black staining on the underside of the roof deck is the signature, and it is visible from inside the attic long before anything shows downstairs.

It can void the shingle warranty

Manufacturer warranties, GAF's included, are written on the assumption the roof is ventilated to code. An inadequately ventilated roof gives the manufacturer a straightforward reason to decline a claim — which people usually discover at the worst moment.

The number, and why we measure rather than count

The building-code rule of thumb is one square foot of net free ventilating area per 300 square feet of attic floor when intake and exhaust are balanced, split roughly half and half between the two.

Net free area is the operative phrase. A vent's opening is not its rating — the mesh and louvres cut it substantially, and a soffit vent painted over three times has a net free area close to zero while still looking like a vent. Counting vents tells you almost nothing. We measure the attic, work out what it needs, and compare that to what is actually open.

The other common fault is mixing exhaust types — a ridge vent plus powered fans plus gable vents on the same attic. They short-circuit each other, pulling from the nearest opening instead of from the soffit, and the attic below stays still.

What we check in your attic

• Soffit vents present, and actually open — not painted, not blocked by insulation
• Baffles at the eaves keeping the intake path clear
• Ridge vent cut to a proper slot width, or just capped over
• Mixed exhaust types fighting each other
• Bathroom and kitchen fans terminating outside, not into the attic
• Black staining or frost on the underside of the sheathing
• Insulation depth and whether it is burying the intake

Straight answers