Re: plate without beam Since there are no beams, take this distance from axle to axle. If you are making headings in columns, you can get h=>l/35. I don't know what kind of load it will have on it, but 20 cm is already a minimum thickness and make sure to check for stapling in columns. Remember, stapling is a type of brittle breakage and it happens suddenly, without action. Also, if you are building a high building, consider whether the earthquake forces will be transferred by 20 cm of flooring, and therefore, whether this thickness is sufficient for horizontal forces. Check both options under semi-rigid diaphragm in ideCAD analysis settings.