Attic ventilation is the least visible part of a roof system and the one most often compromised, usually by accident. In Louisiana, where NOAA’s 1991 to 2020 normals put the August average overnight low at Baton Rouge Ryan Airport at 73.3 degrees and annual base-65 cooling degree days at roughly 2,818, an attic that cannot breathe shortens the life of everything above and below it.
What ventilation is actually for
Two things, and they pull in slightly different directions depending on the season.
In summer, moving air removes heat. An unvented attic under a dark roof in south Louisiana can run well above outdoor ambient on a clear afternoon. That heat radiates down into the insulation and into your ductwork, which is why an AC system in a hot attic works harder for the same result. It also cooks the asphalt in your shingles from below, which accelerates the loss of volatile oils and leads to curling and granule loss years earlier than the warranty anticipates.
In winter and during shoulder seasons, moving air removes moisture. This is the part people underestimate in the South because they associate it with snow country. Every shower, every pot of boiling water, and every gas appliance puts water vapor into the house. That vapor migrates up through ceiling penetrations into the attic. When a cold front drops the roof deck temperature below the dew point of the attic air, the moisture condenses on the underside of the sheathing and on the nail shanks. Do that repeatedly and you get mold on the sheathing, rusted fasteners, and eventually delaminated decking.
Intake and exhaust have to be balanced
This is the concept that gets lost. Ventilation is not a quantity of vents, it is a circuit. Air has to come in low, at the soffits or eaves, and leave high, at or near the ridge. If either half is missing, the other half does very little.
The code reference is the International Residential Code, which Louisiana adopts through the State Uniform Construction Code Council. It sets the baseline at one square foot of net free ventilating area for every 150 square feet of the space being ventilated, reduced to one in 300 where the vent area is split roughly evenly between high and low and the code’s other conditions are met. Net free area is the measurement that matters, and it is not the size of the hole. A soffit vent with a fine insect screen might deliver half the free area its dimensions suggest. Manufacturers publish the figure per unit.
The most frequent real-world failure is blocked intake. A homeowner adds blown insulation, it drifts into the eave cavity, and the soffit vents are buried. The ridge vent at the top now has no supply. Rafter baffles, installed at each bay before insulation goes in, prevent this and cost very little. Any of the roofing contractors in Louisiana you interview should be evaluating intake capacity before they quote you additional exhaust, because adding exhaust to a starved attic does not help.
Blocked intake is the most common version of this, and it is easy to recognize. The air in the attic does not move, it smells like hot dust, and the sheathing above the bathroom reads darker than the rest of the deck. Insulation has drifted over the soffit vents, and the ridge vent has nothing left to pull from.
Mixing exhaust types causes short-circuiting
If a roof has a continuous ridge vent and someone adds a powered attic fan or a set of box vents on the same slope, the fan will frequently draw its air from the nearest opening rather than from the soffits forty feet away. The far corners of the attic stay stagnant. Worse, a powered fan in a leaky attic can depressurize it enough to pull conditioned air up through recessed lights and ceiling gaps, which raises your cooling bill and moves indoor humidity into the attic.
Pick one exhaust strategy per roof plane and let it work. Ridge vent with continuous soffit intake is the simplest and most reliable arrangement for most Louisiana homes.
The unvented alternative
There is a legitimate second approach: seal the attic entirely and bring it inside the thermal envelope, usually with closed-cell spray foam applied to the underside of the roof deck. Done correctly, this eliminates the condensation problem by keeping the deck warm and puts your ductwork in conditioned space, which is a real efficiency gain in our climate.
It is not a casual retrofit. Unvented assemblies have specific code requirements around foam thickness, ignition barriers, and combustion appliance safety, and some shingle manufacturers adjust warranty terms for unvented decks. If a contractor proposes it, ask how they are handling each of those.
Ventilation is now an inspected item
Since August 1, 2025, Act 239 of the 2025 regular session has required parishes and municipalities that issue building permits to inspect roofing work as part of the permitting process, enforcing Chapters 8 and 9 of the International Residential Code for one- and two-family dwellings. Attic ventilation sits in that scope. If your reroof is permitted and inspected, someone other than your contractor is checking that the intake and exhaust math was done. That is a meaningful change from how a lot of reroofs were handled in this state five years ago.
How to tell if yours is failing
Go up on a hot afternoon. If the attic feels dramatically hotter than the outdoor air and there is no perceptible air movement near the ridge, the circuit is not working.
Go up the morning after the first hard cold front. Look for frost or condensation on nail tips and dark staining on the sheathing, particularly near bathroom fans and above the attic hatch.
From the ground, dark streaking concentrated on one slope, shingles that are curling at the edges well before their rated life, or a noticeably wavy roof plane all point back to what is happening underneath
