<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META http-equiv=Content-Type content="text/html; charset=iso-8859-1"> <META content="MSHTML 6.00.2900.2963" name=GENERATOR> <STYLE></STYLE> </HEAD> <BODY bgColor=#ffffff> <DIV><FONT face=Arial size=2>Hello Andrew,</FONT></DIV> <DIV><FONT face=Arial size=2></FONT> </DIV> <DIV><FONT face=Arial size=2>Unless you are examining convection patterns, thermal stratification or other air movement in detail, I don't think you need to be worried about the exact geometry of your stairs. However, It might be a nice idea to include a cube (or 'wedge') of roughly the same mass and surface area as your stairs in the zone you'll create to represent your stairwell. This is simply a matter of creating the vertices you want inside the zone concerned and creating surfaces to represent a closed cube/wedge 'staircase' inside your zone.</FONT></DIV> <DIV><FONT face=Arial size=2></FONT> </DIV> <DIV><FONT face=Arial size=2>You can't have 'holes' in your zones' peripheries. You will have to create a 'fictive' material and construction. This fictive material must have very low density, specific heat, and absorbtion. It must have high permeability, IR emissivity....  It should be transparent too. As if it isn't there.</FONT></DIV> <DIV><FONT face=Arial size=2></FONT> </DIV> <DIV><FONT face=Arial size=2>The construction you create using the fictive material will make up the surface between the 1st floor and the ground floor - your 'hole'.</FONT></DIV> <DIV><FONT face=Arial size=2></FONT> </DIV> <DIV><FONT face=Arial size=2>Olli</FONT></DIV></BODY></HTML>