By default, grids cells are measured from the start and end points of the curtain wall unit baseline. The width of the grid frame is not considered in calculating the size of the cell. For example, if you draw a curtain wall unit with a 14' baseline and a 1' frame on the left and right, and you specify a fixed number of vertical cells, the cells do not appear equal in size. The first and last cells appear smaller because they include the frame. To make the cells equal in size, offset the start and end of the grid by the width of the frame.
Specifying grid offset directions
- Click
. 
- Expand Architectural Objects, and expand Curtain Wall Unit Styles.
- Select a curtain wall unit style.
- Click the Design Rules tab.
- In the left pane, select Divisions under Element Definitions.
- Select a Division definition or create a new one.
- Specify an offset for the grid:
If you want to specify the distance between … Then … the start point of the curtain wall baseline and the start of the first cell in a horizontal grid enter a value for Start Offset. the end point of the curtain wall baseline and the end of the last cell in a horizontal grid enter a value for End Offset. the floor line of the curtain wall and the start of the first cell in a vertical grid enter a value for Bottom Offset. the roof line of the curtain wall and the end of the top cell in a vertical grid enter a value for Top Offset. - Click OK.