Door sills, also referred to as saddles or thresholds, lie along the bottom section of a door frame. It acts to support the bottom portion of the frame. Manufacturers make thresholds from a variety of materials including marble, stone, aluminium, vinyl and wood. Modern homes usually have door sills made from materials that do not rot whereas older homes have wooden door sills. Wooden door sills rot from constant exposure to wet and changing weather conditions. Replacement becomes necessary when the wood rots and exposes the wooden framework under the sill to the elements. This exposure can cause mould and mildew growth or rot to other wood structures located under the door sill.
Equip a circular saw with a carbide tip blade. The purpose for using a carbide blade is because you may cut through unseen nails or screws.
Set the saw blade depth to 6 mm (1/4 inch) and cut through the door sill as close as possible to the doorjamb on both sides of the sill. Increase the blade depth by 6 mm (1/4 inch) and cut along the same cutting path. Continue to increase the saw blade depth by 6 mm (1/4 inch) until you cut through the sill.
Place a flat pry bar at the bottom of the door sill and strike with a hammer to wedge the bar under the sill. Lift away the sill.
Chip away remaining pieces of the sill with a hammer and chisel.
Sand the area lightly with medium grit sandpaper to remove splinters and the rough texture. Fill gouges with an epoxy based putty. Allow the putty to dry and then sand flush with the existing surface.
Measure the opening and purchase a new door sill in the exact size. Choose a door sill made from a material that will not rot such as stone, aluminium or composite materials.
Apply a thick bead of construction adhesive to the underside of the new door sill and position in place. Press down on the sill firmly to set the adhesive.
Place galvanised screws through the pre-drilled holes in the sill and tighten with a power screwdriver if applicable. Door sill materials such as stone, marble and some composite materials do not require screws to hold them in place, construction adhesive will hold the sill.
Apply silicone caulk into the gaps around the door sill.
Wear safety glasses and gloves when removing door sills.