Hi. I hope you folks can help me. I have an old stone house and the interior of the structure is timber framed.

It is a georgian style house with a center hallway/stairwell that runs from front to back and there's one room on either side of the hall.

The summer beam runs through the entire house unbroken - parallel with the front of the house, and perpendicular to the center hallway/stairwell. The joists for the floor in each of the rooms run perpendicular to the summer beam, tying into it with mortise and tennon joints.(I have not ever seen the top of these joints so it's possible that they are dovetail tennons) On either side of the hallway/stairwell, there are larger joists (4 x 8) that tie into the summer beam (the walls on either side of the hallway rest atop these larger joists), and between these Large joists there are beams tied into them using through tennons that support the flooring of the hallway.

It is with one of the larger joists that I am having a problem. It has cracked at one of the through tennons and the doorway above has sagged as a result. How do I replace this beam? What species of wood should I use and does anyone have any suggestions on how to support the wall above while I remove the damaged timber?

Or could you recommend a guild member from the Philadelphia/Lancaster area?

Thanks for any help or direction that you can give.