Install the Frame
Exterior shutters are often mounted on a three-sided frame so that there is no frame piece along the window sill. This type of design is neater and allows rainwater to run off the sill easily to prevent problems with rot or mildew. Because exterior shutters are exposed to the elements, make sure you choose hardwearing or factory-coated materials.
Construct the frame as specified, unless it is supplied ready-made. Position the frame at the front of the recess (Image 1). Check the fit.
Use a level to check that the frame is square (Image 2). If shimming is required, get help holding the frame while you make any adjustments.
Mark the predrilled hole positions on the wall (Image 3). If holes are not predrilled, then attach each piece at the top, bottom and center.
Remove the frame and drill the pilot holes using a suitable bit (Image 4). Plug the holes if necessary, then reposition the frame and attach it in place. Do not over tighten the screws, you might distort the frame.