Classic doors require headroom of 300mm, and side room of 70mm or 90mm.
Compact doors require 205mm headroom and 70mm side room
The bottom lath will hand down into the opening, so will reduce the drive through height by 77mm or 55mm respectively.
If the door is installed between the opening the drive through widen will be reduced by twice the guide width, and the drive through height will be reduced by the headroom requirement and the bottom lath size.
Where will my door fit?
Internal Face Fix
Where there is sufficient side and headroom, the guide rail and roller assembly would be installed directly to the inside of the garage opening. This is recommended for most installations.
Installed between the opening and is good where there is limited side or headroom inside the garage. This will reduce drive through height noticeably.
External Face Fix
Fitted to the external face of the garage, useful where there is not enough space to install on the inside face, but where maximum drive though space is required.