Because the floor was due to be replaced and lowered 8 inches, it was imperative to deepen and strengthen the footings, which were mostly only two or three bricks deep. They were built down a metre by digging a trench in sections around the house. New bricks were laid almost direct onto the clay, on a thin layer of limecrete.
Most of the oak sole plates supporting the walls, laid onto the old brick footings, were rotten. They were replaced with the same wood, oak.
To do this, the specialist builders we contracted jacked up the walls of the house section by section, about 12 feet longitudinally at a time, using steel girders on steel props. The girders were put through holes – made as small as possible – in the walls just below first floor level, so that the beams that support the first floor could rest on them. The walls were hardly lifted; rather, the plan was to take the weight off the old sole plates and footings, build the new footings, re-using as many of the old bricks as possible, and raise the wall just enough to extract the the old timbers and insert new oak. Girders were also put through to support the old sole plates while the new, deeper, brick footings were being built.
With the timber frames and infill panels of the ground floor effectively hanging from the beams above, mortices were cut into the new green oak sole plates to take the tenons of the original oak studs. The props were lowered, the studs connected with the sole plates, the sole plates transferred their weight to the new footings and oak dowels were inserted to lock the studs to the plates. Then the team moved on to the next section. No concrete underpinnings were used. The footings and the sole plates will be continue to flex with the building.
Sadly, a few sections of wattle and daub fell out as the walls were lifted, including two complete panels. But the clay was collected and re-used and the panels were remade with hazel sticks and new clay daub mixed with the old material (see wattle and daub post). This seemed a small price to pay for a long-lasting repair of the whole building with new sole plates and footings. There are practical limits to how far one can preserve every bit of old material when working to preserve an ancient building. But the basic intention is to keep as much as possible.