The soffit is the finished underside of the roof overhang, the board or panel that closes the gap between the wall and the fascia. On most St. Louis houses it is aluminum or vinyl, and it is either perforated to let air through or left solid. That choice affects how the attic breathes, how the eave holds up to wind and hail, and how the crew reaches the nailing strip on the day the new roof goes on. It belongs in the spec before the order goes in.
Material and spec
A vented soffit panel has small perforations or slots that let outside air enter the attic at the eave. Paired with a ridge vent or another exhaust at the top of the roof, it forms a balanced system where air moves in low and out high. A solid soffit has no openings. If the old soffit was vented and the new one is solid, the attic loses its intake unless another intake is added, and the roof can run hot in summer and hold moisture in winter. The residential code sets attic ventilation as a ratio of attic floor area, commonly one square foot of net free vent area for every 150 square feet of attic floor, with a lower ratio allowed under some conditions. The spec should state the net free vent area the design is meant to deliver, not only the word vented.
Aluminum soffit is the common product. It is light, it takes a factory paint finish, and it can be perforated or solid. It dents under hail and under a ladder, and a dent in a painted panel shows where the paint has broken. Vinyl soffit often costs less per linear foot in quotes and does not need paint, but it moves more with temperature. A vinyl run fastened tight on a cold morning can buckle on a hot afternoon, so the installer should leave the expansion gaps the manufacturer calls for. Vinyl can also crack when it is struck in very cold weather, which is a real risk on a January morning in St. Louis.
Where each one fails
Perforated aluminum fails most often at the fastening. A panel held by too few nails can sag between the fascia and the wall, and the perforations collect insects and dust if the screen behind them is missing or torn. Solid soffit fails when the attic has no other intake, which is a design problem more than a material problem. Vinyl fails at the joints when expansion gaps are closed, and at the corners where a crew has forced a piece into a space that was measured wrong.
Both materials depend on the nailer behind them. The soffit is fastened to a board or to the framing at the wall and the fascia, and rot in that board lets the panel pull away. A soffit replaced over soft wood will sag again within a few seasons, so the crew should look at the nailer before the new panel goes up. That check belongs in the same walk where the rafter tails and the fascia are examined.
What St. Louis asks of an eave
The local conditions show up on a St. Louis eave every year. Freeze and thaw cycles push water into the seams of the fascia and the soffit, and that water is what rots the nailer. Spring hail and summer straight-line wind lift the edge of a loose panel and tear it off the fascia. Heavy summer sun fades a painted panel, and it fades faster on a south or west face. In winter, ice damming at the eave can back water up under the shingles and into the soffit area if the vent path is blocked by insulation or by a frozen vent screen.
The attic is where the soffit spec connects to the rest of the roof. Air that enters at the soffit has to reach the ridge without passing through insulation that has been pushed against the eave. If insulation sits in the soffit path, the ventilation the spec promises will not happen. Ask the roofer whether insulation baffles at the eave are in the scope or whether they are left to the homeowner.
What it costs
Soffit is priced by the linear foot, and the difference between vented and solid panels is usually small compared with the cost of the fascia, the nailer repair and the trim pieces that go with it. The bigger cost difference comes from replacing a whole eave versus patching one section. A run that has to be removed to reach a rotted nailer adds labor no matter which panel goes back up. Ask for the soffit as its own line, with the material, the finish, whether it is vented or solid, and the net free vent area. Then compare those details across bids, not the price per foot alone.
What to ask
Ask each roofer whether the soffit is vented or solid, and what the attic intake will be after the work. Ask for the material and the finish, and ask whether the finish carries a stated warranty from its maker, without treating a verbal promise as a warranty. Ask how the panels will be fastened, how many nails go in each piece, and whether the nailer will be inspected or replaced if it is soft. Ask how expansion gaps will be handled on vinyl and whether the insulation at the eave will be checked for blockage.
Ask for the soffit detail in writing before you sign. A written scope that names the panel, the vent type, the nailer treatment and the expansion allowance gives you something to check on the day the crew leaves. Keys Roofing puts a written scope with photos and measurements in the homeowner's hands, and the soffit belongs on that page. If you want to talk through the detail before you choose, the office number is (314) 220-2333.