Bad Goat Designs and Builds Timber Frames, like this Barn.  Timber Frames can often be built in stages.  In this case the main/center bent is assembled, and all the joinery has been added for the futured addition of a shed roof bent off each side of the main frame.  That is why there are oak splines protruding from both sides of this frame.  This frame is 16×24 as is, with the option to add 2 shed roofs of 12×24 off each side.