Dear сolleagues,

I would like to take an advise about wood framing. 

I work on heavy timber 4(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 in advance.