Decide whether your door is to open left or right-handed, and purchase two or three 100mm (4in) hinges and handles accordingly.
Purchase a door that is marginally larger than the available space, as frames are rarely completely square. The new door will need to be trimmed to fit, however, no door should be excessively trimmed as this will weaken its structure, and in the case of flush doors, no more than a couple of millimetres can be removed from any side.
Measure the width of the doorframe at the top and the bottom and subtract 4mm from these measurements to allow a 2mm (<⅛in) on each side. Measure the height at the left and the right and subtract 8mm from the height measurement to allow a 2mm (<⅛in) gap at the top and a 6mm (¼in) gap at the bottom.
Transfer these measurements to the door, ensuring that you plane wood away evenly from opposite sides to maintain the door’s symmetry.
When planing wood from the top and bottom, work inwards from the outer edges to avoid splitting the wood.
Support the door on a couple of wedges and test its fit in the doorframe.
Once the fit looks to be correct, support the door at the right height on wedges, but prop it in an open position. Placing the hinges with their knuckles facing into the room that the door opens towards, mark the top and bottom of both hinges on the edge of the door and the doorframe. Hinges should be recessed equally into the door and the door frame.
The upper hinge should be positioned 175mm (7in) from the top of door and the lower hinge should be placed 250mm (10in) from the bottom. A third, central hinge should be added to heavy hardwood and exterior doors, fire doors and those doors fitted to areas where the interior will be hotter than the exterior, for example on airing cupboards.
Place the door on the floor, latch side downwards. Place each opened hinge in the appropriate place on the upward side and draw accurately around each it, marking its depth too.
With a chisel and hammer, remove this shallow marked area of the door by first cutting around the edge, then making several cuts across the grain such.
Test each opened hinge in its recess to ensure it sits flush and flat. Drill pilot holes, using the hinge as a template, and then attach the hinge to the door with 25mm (1in) screws.
Using wedges, place the door in an open position against the door frame and check the marks made for the hinges. Chisel away the marked areas as before and drill pilot holes.
Screw the door and hinges to the frame using just one screw per hinge, before testing the door function. Make any further adjustments necessary to ensure the door swings freely ; this may involve planing a little more from a ‘sticky’ edge, or positioning a layer of cardboard beneath a hinge if it has been too deeply recessed and the door is straining against it.
Add all remaining screws.