In which sequence should you flash a door or window?

The correct approach to flashing a door or window is to start at the sill, followed by the jambs, and then the head. This sequence is important for effectively directing water away from the structure.

Beginning with the sill allows any water that might leak in around the bottom of the door or window to flow away from the building rather than being trapped. Once the sill is properly flashed, proceeding to the jambs ensures that the sides are sealed against moisture. Finally, finishing with the head ensures that any water coming down from the top of the window or door can drain away without bypassing the other flashing.

This method is crucial as it follows the principles of proper water management, ensuring that the most vulnerable areas—the sill and joints between the window frame and wall—are protected first, which effectively reduces the risk of leaks and water damage.