When interpreting building or architectural terminology it is important to recognise that they generally talk in overall widths and drops (height). That is opening sizes. For example if they were talking about a 900 mm wide by 2100 mm drop sliding door, they would say it was a 1800 sliding screen door. This then becomes confusing, as you would think based on that description that the overall door required was 1800 mm. This however is not the case as the actual opening size is only 900 mm. Therefore the door required is 900 mm, not 1800 mm.
The same terminology would apply to a door with an opening of 1200 mm. A builder may describe this as a 2400 mm sliding door, this is a correct description of the overall brick to brick opening. It is not however a correct description of the opening size for the security /screen door required.
As you can see, confusion with this terminology to the lay person can be easily misunderstood. A couple of questions to either your builder or designer architect to clarify the actual opening size of the door required can save a considerable amount of confusion.
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