By looking from the inside of the sub-floor, I have been able to see that a pvc exterior door has been installed not directly onto the brickwork, which is rather old and crumbly, but onto a length of timber. Further, on the exterior, the rendering has been taken right down to ground level, beyond the dampcourse. A surveyor recommended that the render be cut back above the dampcourse, but this presents the problem of a chunk of wood being exposed to the elements. Presumably the timber should be replaced with brick, but is this possible to do with the door still in situ?
Usually, yes, but as you pull the timber out, chock the frame up with something suitable ( bricks ) at reular intervals. When you start laying the bricks in the hole properly, take out the "chocks" one at a time as you get to them. This will ensure your frame does not drop as you work.