What is the four holes?

Refers to stairs, elevator wellheads, reserved holes and manholes.

Four holes refer to four holes in the building, including stairs, elevator wellhead, reserved holes and manhole, which are very important four holes in the building.

In the process of building construction, four openings must be protected, and fences, cover plates and nets should be set up at stairs, elevator entrances and reserved openings. The population, tic-tac-toe frame and portal frame of the building under construction must set up protective sheds that meet the requirements.