Third in a series of timber framing joint articles by Jack Sobon, author of a great book on timber framing. His diagrams make understanding even complicated joints easy.
Personally I find the sill and floor joints to be some of the most interesting. Sadly they are almost always hidden from view once the timber frame building is fully standing.
Just as the plates and tie beams hold together the upper part of the timber frame, the sills tie the posts at the foundation level. Though not subjected to the same stresses as tie beams above, sillskeep the bottom of the building from spreading. Many old structureswhose sillsaredecayed are noticeably wider at the bottom. Sills also distribute column loads over the foundation, act as bond beams to hold together the top of the stonework and stiffen and support walls and the first floor. … (found at scribd.com)