Green oak has a much higher moisture content than seasoned timber, this moisture is gradually lost over time causing the wood to shrink, particularly in the first few years.   Shrinkage is one factor that is guaranteed when using green oak.   The natural seasoning process does not weaken the structure, but makes the oak harder and stronger as it dries. In fact, oak is high density and has a strength/weight ratio superior to steel, giving it great load-bearing capabilities.
Oak shrinks in width, not length, so there is no risk of a tennon slipping out of a mortice. Cracks and splits have very little effect on the structural integrity of the frame. As the grading system limits the angle at which the grain runs along a piece of oak, the splits which open up along the grain as the fibres dry and separate do not traverse the beam’s grain and therefore do not weaken it
Another part of the appeal of oak is that is does not need to be “finished” – externally the sunlight weathers to a beautiful silvery grey.  However, if you wish to retain the rich colour of green oak for your particular build, then that is possible by using wax oil treatments (although this can be a labour of love!).  Internally, oxidation makes the green oak a honeyed colour over time, bringing a warm ambience to your home.