Original fabric

Over time, the original fabric and structure of a building may deteriorate or the building may become unstable. The ground beneath a building may rise (heave) or fall (subsidence) and may also distort horizontally. This can cause cracks and distortion and may make the building unsafe.

Timbers shrink by about 15mm along their length in 100 years, so the end bearing of rafters and joists must be checked.

Signs that the ground may have moved under a building include an uneven roof line, structural cracks in the wall, and sagging or slanting windows or brickwork. Traditional underpinning involves spreading the load of the building by strengthening the foundations, but is often not necessary and is rarely the best solution.

When an extension or new building is constructed next to an existing building, there will inevitably be ground movement, and this must be allowed for. In the case of an old building with a stable structure, but which cannot take additional load, an inner timber frame may be tied to the existing framework. The space between the new and original frameworks allows for insulation of the walls.

Old lime mortars and timber-framing allowed seasonal movement of buildings. Modern cements are so hard that they cannot accommodate movement and can lead to more problems for a building.