Apartment-type folding doors are constructed in the residential space where we live, so we need to proceed with the construction with the frame of the folding door accordingly. If it is constructed with a folding door that does not fit the construction site, inconvenience may occur. Therefore, the general folding door lower rail and the apartment-type folding door lower rail are manufactured differently from the blueprint.
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The lower rail of the general folding door is made with a total height of 40mm, and the height protruding above the floor surface during construction is about 3~4cm. In that regard, you can feel a great inconvenience in an apartment (residential space) where you live without shoes.If you get caught in the lower rail without shoes on when passing, you may be seriously injured, and it may also be difficult to move large objects to the veranda.​​​

Therefore, the minimum height protruding above the bottom surface was minimized with the minimum slim lower rail to be exposed to about 15 cm.This is also called a slim lower rail or a 23mm lower rail.