Find Where the Draft or Moisture Is Entering
A draft at a window does not always come through the same place. Air can move around the sash, through worn weatherstripping or through perimeter gaps between the frame and the wall.
The first step is to identify the likely path before adding more sealant. A failed glass seal, rotted frame or damaged window unit will not be corrected by caulking the perimeter, so weatherproofing should stay focused on gaps and seals that are actually repairable.
Exterior Sealant and Perimeter Joints
Exterior joints around the window need to shed water while accommodating normal movement between different materials. Cracked or separated sealant can allow water and air to reach the opening.
Old failed caulk may need to be removed so new material can bond properly instead of being layered over a loose surface. The adjacent siding, trim and flashing should also be considered if the gap appears to be part of a larger exterior-envelope problem.
Interior Gaps, Weatherstripping and When Replacement Is Better
Interior weatherstripping helps control air movement around operable sashes when the window itself is still functional. Small gaps at trim transitions can also be addressed where appropriate.
If the frame is rotted, the sash is damaged or the insulated glass has failed, weatherproofing alone may not solve the problem. Window Frame Repair, General Window Repair or full Window Installation & Replacement should be used when the defect goes beyond sealing the existing unit.