A wet patch in the attic after a hard St. Louis storm does not automatically mean the shingles leaked. Rain pushed sideways by wind can enter a gable vent, cross the attic on moving air, and wet rafters, insulation or the ceiling below. The clue is often a wet area near the end wall rather than directly below a roof penetration. Before anyone recommends shingles, flashing or sealant, the vent itself needs to be inspected from both sides.
Storm and hail
A gable vent is the louvered opening high on an exterior end wall. Its job is to let attic air move while keeping ordinary rainfall outside. Most vents accomplish that with angled blades, an insect screen and a frame sealed to the siding, brick or trim. Those parts can perform normally for years and still admit water during a storm that combines heavy rain with wind aimed at that wall.
Wind-driven rain does not fall straight down. It can strike the wall almost horizontally. Water reaches the louvers, splashes against the screen and breaks into small droplets. Air moving through the vent can carry those droplets into the attic. Once inside, the water may run down the back of the wall, follow a brace, drip from a nail or collect on insulation several feet away.
That travel makes the stain misleading. A ceiling mark six feet from the gable wall may still begin at the vent. Wet fiberglass insulation can spread water sideways, and roof framing can redirect it before it drops. A roofer should trace the wet path toward its highest point instead of assuming the opening is directly above the stain.
Hail adds a different question. It can dent a thin aluminum vent, crack a vinyl louver or loosen brittle sealant around the frame. A dent by itself does not establish that water entered. The useful evidence is a split, displaced blade, open frame joint, torn screen, impact opening or a clear water path on the attic side. The surrounding siding and trim should also be checked because water entering above the vent can appear to come through it.
How the source is separated from a roof leak
The first inspection should start in the attic before the wet materials dry completely. A flashlight can reveal dark water tracks, damp dust, wet fastener points and droplets on the back of the vent. The inspector should photograph the vent, the framing below it, the insulation and the route toward the interior stain. A moisture meter can help define the wet area, but it does not identify the entry point by itself.
The roof above the gable still needs attention. Shingles near the rake edge, flashing at any wall transition, ridge cap, nearby pipe penetrations and the roof deck should be checked. If those surfaces are dry while the vent and end-wall framing are wet, the evidence points toward wall entry. If the decking is wet above the vent, the water may be arriving from the roof and merely passing behind it.
A controlled water test can narrow the source when visual evidence is not enough. It should be done in sections, starting low and allowing time between each section. Spraying the entire gable at once proves only that water can get inside somewhere. It does not show whether the opening is a louver, a perimeter joint, cracked siding or flashing higher on the wall.
The direction of the storm matters too. If water appears only when strong wind comes from the direction facing the vent, that pattern is useful. It is not proof on its own, but it tells the inspector where to concentrate. St. Louis thunderstorms can change wind direction quickly, so a vent that stays dry through ordinary rain may leak during one particular front.
The repair depends on how the water entered
There is no single correct repair for every leaking gable vent. If the frame has separated from the wall, it may need to be removed and reset with proper flashing and compatible sealant. If a louver is cracked or bent open, replacement may make more sense than trying to reshape it. If water is being pulled through intact louvers, a baffle on the attic side may reduce direct entry without closing the ventilation opening.
A baffle must be designed so air can still move. Covering the vent with plastic or plywood may stop rain, but it also removes part of the attic ventilation system. That can leave warm, moist air trapped against the roof deck. During the St. Louis freeze thaw cycle, moisture can condense on cold sheathing, frost over, thaw and create staining that looks like another leak.
The vent also should not be changed in isolation. Some attics use gable vents as the primary exhaust. Others have ridge vents, roof vents or powered fans. Mixing intake and exhaust paths can short-circuit airflow, pulling air from one upper vent to another instead of from the soffits across the roof deck. Before reducing or removing a gable vent, the roofer should identify the attic's intake area, exhaust area and actual airflow path.
Ice damming at the eave is a separate problem. It begins lower on the roof when heat loss melts snow and the water freezes again near the cold edge. A gable vent repair will not correct missing soffit intake, air leakage from the house or inadequate insulation at the eave. If the attic shows both gable water entry and frost near the roof deck, those conditions should be documented separately.
What it costs
The price depends less on the size of the vent than on access and wall construction. A small vent above a one-story roof may be reached and reset without much staging. A vent high over a steep roof, masonry wall or narrow side yard can require additional equipment and labor. Interior baffles, damaged sheathing, wet insulation and finish repairs are separate parts of the work.
A written price should say whether the contractor is sealing the existing frame, removing and reinstalling it, replacing the vent, adding a baffle or repairing surrounding trim. It should identify the vent material and the wall surface. It should also state whether wet insulation removal and replacement are included.
Be cautious with a quote that lists only caulk. Exterior sealant has a proper use at selected joints, but it is not a substitute for flashing or a sound vent frame. St. Louis heat, winter cold and repeated freeze thaw movement can open a poorly prepared bead. The proposal should explain what failed and how the repair addresses that path.
If the work includes structural sheathing, framing or a substantial exterior alteration, ask which municipal permit desk has authority over the address. St. Louis County contains many separate municipalities, and requirements are not identical from one desk to the next. The contractor should verify the applicable requirement rather than treating the county as one permit jurisdiction.
What to ask
- Where is the highest visible point of moisture?
- Is the roof deck above the vent wet or dry?
- Did water pass through the louvers, around the frame or from higher on the wall?
- Is the vent cracked, displaced or merely dented?
- Will the proposed repair change the attic's intake or exhaust balance?
- Does the scope include wet insulation and damaged interior material?
- What wall and vent materials will be removed and reinstalled?
- Who will confirm whether the municipality requires a permit?
Ask for photographs that connect the exterior condition to the interior water path. A close picture of a dent is not enough. Useful documentation includes the full gable, the vent perimeter, individual openings, the attic side, wet framing and moisture readings at identified locations. Keys Roofing can document observed damage and provide the homeowner with a written scope, photos and measurements. The homeowner remains responsible for any communication with an insurer.
Call Keys Roofing at (314) 220-2333 if rain appeared near a gable wall and you need the roof, vent and attic checked as separate possible sources. Leave wet insulation undisturbed until the entry path has been photographed, unless moving it is necessary to prevent further interior damage or address an electrical hazard.