What is the required finished opening measurement for a bifold door?

For a bifold door, the required finished opening measurement is determined by the space needed to accommodate the door panels and their hardware when they are in motion. Choosing to add additional width to the door itself allows for clearance, ensuring that the bifold door can open and close smoothly without obstruction.

When installing bifold doors, it's generally accepted in the carpentry trade that the finished opening should be slightly less than the actual door width. This includes consideration for the thickness of the door panels and the hardware, ensuring that they can fold and stack properly without overlapping or binding.

If the finished opening were greater than the door width, it would lead to insufficient door support and an unsightly gap when the doors are closed. Thus, subtracting the appropriately specified amount ensures a proper fit, allowing for both aesthetic appeal and functional operation of the door. This reasoning confirms that measuring the finished opening as the door width minus 19mm is the accurate approach for bifold door installations.