Stairs will not directly attach (using the Attach Top/Base command) or join (using the Join geometry command) with wall elements. If you are working with straight stairs, you can use a reference plane aligned with the bottom of the stairs, and attach the stairs to the reference plane. Alternatively, you can directly modify the profile of walls to fit with the stairs.
When looking online for the topic of joining walls to stairs, I found the following pages with additional information:
thks for the information...
actually i'm build modeling for paint area calculation.....
i need to joint stair with wall because... i need to deduct area from side of wall....
if not ... the area calculation will calculate all the wall surface...
u have any method???
p/s: sorry for my bad english language....
You could try editing the profile of the wall to exclude the area of the stairs (from an elevation or section view).