We follow the door installation process that is standard across Europe.
The diagram beside shows the basic requirements to install a door set. Ideally you should put in a subframe made of 30mm softwood or 18mm ply screwed securely to the brickwork. In a new build this enables you to make an accurate opening and be able to plaster up to it. Then you will be able to install these door sets at the last minute, after all decoration has been completed. As the diagram shows you should allow 50mm on the width and 30-40mm on the height (from the finished flooring height).
So if the door is 762mm, the opening is 762+50mm = 812mm
With this subframe in place it allows you to fix the veneered frame in place ideally using corrugated staples using a high powered staple gun. Our preferred subframe material is 18mm plywood which should be full finished wall thickness. These will be hidden once the architrave is on. On the hinge side of the frame, replace a hinge screw with 1 long screw in each of the four hinges. You can also put longer screws through the striking plate. This method of fixing will leave the frame without any noticeable fixing marks. You can see the types of locks and hinges used by clicking the links.