In this video, This Old House general contractor Tom Silva shows how to prevent water from leaking in behind vinyl siding.
Steps:
1. Inspect the area above the leak, including both indoors and out.
2. Check to be sure weep holes are open along bottom of window openings.
3. Use a caulking gun to apply a continuous bead of silicone sealant along the vertical seams between the vinyl J-channels and the exterior window casings.