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Last Updated: 16 February 2021

2.1.8 - Open a hole in the basement roof slab for the stair

A.- Interference Condition

To operate the stair, you need to open a rectangular hole in the roof slab, long enough for someone going up not to bump his head, as shown in Fig.2.1.8.3.
To open a hole in the roof slab of the basement,  you will add an interference condition between the stair and the slab.

With the interference condition, you can Add or Subtract other objects to a slab. The Subtract option removes the mass element from the slab.

Stair that is applied as interference condition in roof slab, can be edited like any other object using grips, or on properties palette. If you edit stair, and change width, height, headroom height, etc, the roof slab updates accordingly.

When you add an inerference condition between the stair and and the roof slab, a box is cut around the stair, based on the stair's specified headroom height and side clearances.

The length of the hole is set in the Properties Palette (Fig. 2.1.8.1) of the stair, in the category Advanced > Interference > Headroom height.
The Headroom height defines the clear height between beam and slab at the edge of the hole (Fig.2.1.8.1).

To open a hole in the basement roof slab for the stair:

• For your own convenience hide the wall (bg), to have a better 3d view of stair and slab (Fig.2.1.8.1).
• Double-click the stair to open the properties palette (Fig.2.1.8.1).
• Click the Design tab, expand Advanced, and expand Interference.
• Specify the height above the threads for the interference condition. At this stair, for Headroom height enter the value 2.10 (as shown in section at Fig.2.1.8.3).
• Click Esc, to remove the selection of stair.
• Select the slab, on the roof of the basement, to intersect.
  On Ribbon > click Slab tab > on Modify panel select Interferencee Condition drop-down > and then select Add icon . 
• At the prompt: Select Object to Add: select the stair, and press Enter.
• At the prompt: Enter Shrinkwrap effect: select Subtractive and press ENTER.
• Press the ENTER button again to end the command execution.

The result is as shown in Fig. 2.1.8.2.

Save this drawing under the name h21190_basement in the folder customDwg\basement you have created. It's full path will be:
C:\ACA\myProjects\house21_190\customDrawings\basement\h21190_basement.
You will use this drawing in chapter 5, to create the construct drawings of the basement.

To remove the hole in the basement roof slab:

• Select the slab, in the roof of the basement, from which to remove the interference condition.
• On Ribbon > click Slab tab > on Modify panel select Interferencee Condition drop-down > and then select Remove icon . 
• At the prompt: Select Object to Remove: select the stair, and press Enter.
• Press Esc to end the command execution.

The next lesson is 2.2. The Ground Floor plan