First determine whether the moisture is rainwater

Not every wet threshold is an exterior leak. Identify the timing and water characteristics before opening the assembly.

• Wind-driven rain: appears during storms, often from a particular direction.
• Snow or ice melt: follows accumulation against the sill, storm door or landing.
• Condensation: forms when warm, humid indoor air meets cold glass, metal or another cold surface.
• Cleaning or household water: may be isolated and unrelated to exterior conditions.
• Plumbing or wall leakage: may continue without rain or appear above and beside the opening.

Ask when the moisture first appeared, which way the wind was blowing, whether a storm door was closed and whether the homeowner wiped the area before photographs were taken.

Water location and likely source

A contractor’s top-to-bottom diagnostic process

1. Document the site before disturbing it

Photograph stains, wet flooring, swollen trim and exterior conditions. Record recent rain, wind direction, temperature, snow, roof runoff and irrigation. Use a moisture meter where appropriate and map readings beyond the visibly wet area.

2. Inspect above the door

Check roof edges, gutters, porch roofs, head flashing, siding joints, masonry and penetrations above the opening. Water can enter at the head, travel down a jamb cavity and appear at the sill. Repairing the bottom will not stop an upper-wall source.

3. Check exterior drainage

The porch, stoop or landing should direct water away rather than hold it against the threshold. Look for reverse slope, settled concrete, snow traps, mulch, caulk dams and a storm-door channel that overflows toward the entry.

4. Inspect the sweep and sill contact

Look for torn, wrinkled or missing sweep components. Check contact across the entire threshold. A sill that is humped or depressed beyond the sweep’s range can leave gaps even when the center appears tight.

5. Check corner seal pads

On applicable inswing systems, corner pads bridge the lower transition among vertical weatherstrip, sill and door bottom. Therma-Tru identifies missing pads as a potential source of air leakage; incorrect lower-corner sealing can also contribute to water intrusion under exposure.

6. Inspect jamb-to-sill joints

The joint where each jamb meets the sill must remain sealed. Therma-Tru’s troubleshooting guidance calls for restoring the seal at this location with the specified type of compatible sealant and reinstalling the weatherstrip and corner pad correctly.

7. Check frame alignment

Inspect reveals and weatherstrip contact. A sagging slab, twisted jamb or unlevel sill can create a leak path. Confirm plumb, level, square and plane before attempting to solve the issue with additional seals.

8. Inspect perimeter sealant and flashing

Look for cracked, missing or detached sealant at brickmould and cladding transitions. Determine whether head flashing and the water-resistive barrier direct water outward in a layered sequence. Surface caulk cannot replace missing flashing behind the trim.

9. Investigate the sill pan and subfloor

When evidence points below the unit, trim or the door may need to be removed to inspect the concealed condition. A sill pan is intended to collect incidental water and direct it outward. The sill also needs a level, solid bearing surface and the specified seal beneath the system.

10. Test methodically

Controlled water testing should begin low and move upward one area at a time, allowing enough time to observe each step. Do not flood the entire facade with a high-pressure nozzle; that can force water through joints beyond normal exposure and destroy the ability to identify the source.

What a sill pan does—and does not do

A properly integrated sill pan provides a secondary drainage path beneath the door unit. It helps manage water that reaches behind the frame or sill and directs it toward the exterior.

A sill pan is not permission to ignore the primary seals. It must be sized, joined, sloped or supported as designed, sealed to adjacent materials and integrated with flashing. Its exterior drainage path must remain open. Incorrect sealant placement can defeat the system.

Sill adjustment vs. sill repair

An adjustable sill cap can improve contact with the door sweep when the assembly is otherwise sound. Therma-Tru describes testing contact with a dollar bill: it should pull out with resistance but without tearing at each adjustment point.

Adjustment is not a repair for a cracked, bowed, corroded, loose or unsupported threshold. Raising the cap aggressively may make the door hard to close while leaving the underlying water path untouched.

Quad Cities exposure and wind-driven rain

Wind can push water upward and sideways through weaknesses that remain dry during gentle rain. A west- or north-facing Davenport entry without a deep porch may experience very different exposure from a protected Bettendorf doorway.

Document the direction that triggers the leak. Also check gutters, downspouts, roof valleys and nearby walls. The door may be where water becomes visible, not where it first enters.

Repair decision table

When the frame should be replaced

Complete replacement becomes reasonable when water has softened lower jambs, damaged the sill, rotted the subfloor, distorted the frame or revealed a fundamentally poor installation. Reusing compromised components transfers known risk into the repaired opening.

Review when to replace an exterior door frame before committing to a slab-only repair.

Protect the interior and exterior finish

Water diagnosis can become destructive if trim is removed without a restoration plan. Photograph casing and siding, score paint joints, protect flooring and define which finishes will be repaired. After the source is corrected, allow wet materials to dry and replace damaged porous materials as appropriate before closing the assembly.

A neat caulk bead is not proof of a durable repair. The best-looking result is a properly layered system with restrained, compatible exposed sealant.

Common leak-diagnosis mistakes

• Caulking the first wet joint. Water may be traveling from above or behind the frame.
• Blocking the sill’s drainage path. More sealant can trap water inside the assembly.
• Testing with excessive pressure. A hard spray can create leaks that normal weather does not.
• Ignoring landing slope and roof runoff. The door cannot manage unlimited exterior water.
• Adjusting the threshold beyond its range. This can damage the sweep and operation.
• Closing wet materials inside the repair. Correct the source, evaluate damage and allow proper drying.

The bottom line

Water under a front door requires a path-based diagnosis. Inspect from the roof and wall down to the sweep and subfloor, then verify the suspected source with controlled testing.

The ruthless rule is simple: never use surface caulk to hide a water-management problem you have not traced. Stop the source, preserve drainage and rebuild damaged layers correctly.

Frequently asked questions