When installing windows, I like to pad up the opening with a scrap 1/2″ x 5 1/2″ clapboard to create an outward pitch on the rough window sill. This does require planning ahead at the framing stage to allow for the additional 1/2″ that the clapboard will take up. This gives me the peace of mind that if water penetrates, it will flow back out to the exterior down the water-resistive barrier to safety and not to the interior finishes of the building.
