Drips Beneath Window Sills
(1) Except for wall openings located less than 150 mm above ground level, where a concealed flashing is not installed beneath window and door sills, such sills shall be provided with an outward slope and a drip located not less than 25 mm from the wall surface.
Article 22.214.171.124 Ontario Regulation 332/12 Building Code, Information published by oncodes.ca for educational purposes only.
Drip flashings intercept moisture that has entered behind the cladding and direct it to the outside, as well as redirect water flowing down the face of the wall to prevent it from dripping down on the materials below. A drip flashing should be inserted between two different siding materials (for example, siding above stucco) or between different materials and components. To prevent water from entering the joint, a preformed drip should extend from behind the siding out over the stucco to a drip at the outside edge.
Note: Flashing should also be used over windows and doors (drip flashing in this location is also called “head flashing”), unless they are protected by an overhang. This flashing is required where the vertical distance between the window or door and the underside of the overhang is more than one-quarter the horizontal projection of the overhang. For example, flashing is required if the top of a window is more than 300 mm (12 in.) below an eave that projects 1.2 m (4 ft.). Head flashing should extend from the top of the window or door to up and under the sheathing paper or membrane.
Where the sills of windows and doors in exterior walls are not self-flashing, flashing must be installed between the underside of the window or door and the wall below.