Hello, 

I would like to take an advise. 

I work on heavy timber(wood framing) constructions now and try to make optimal spans for columns in the building.

Who already has expirience in that, could you say what beams(dimensions) should I use for floring if I would like to make 20' spans between colums? 

Is it possible at all? 

If not, is it possible to make 15' spans?

I know what beams to use for 10' spans, but I feel that it is possible to make it larger. Isn't it? 

I understand that the best option would be to calculate the load, but I think there are some standarts in Heavy Timber or wood framing in general, which can help without calculation. Please notice, there are 2 floors and a flat roof. 

I am looking forward to your advise. 

Thank you very much.