Assuming I understand... Walls are always determined from their middle point, so if you thicken a wall, it will grow in both directions.
You can set [font=courier new]Preferences - New wall thickness[/font] before you double-click with the room tool to create walls. But that does not work if you want a room with different thickness walls.
What is easier, may be to adjust both thickness and position of each wall afterwards to fit the room. (In your ase, the left wall X values should be some -10 cm compared to the original value.)
That may be true. But a wall can be measured on the outside or on the inside and therefore have different lengths depending on different wall thicknesses. And which direction should an inner wall grow if thickness is increased? Cannot find the thread off-hand, but in the forum somewhere there is a discussion about this where Puybaret explains why. ok