In this video, This Old House general contractor Tom Silva shows how to prevent water from leaking in behind vinyl siding.
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.