The short answer
Gently, and in proportion to the fault. A roof on a timber-framed house has moved with the building for centuries, so repairs work best when they follow the existing shape and keep as much of the old covering as is sound. A full strip is a last resort, and is chosen only when the timbers underneath show it is needed.
East Hagbourne was part of Berkshire until the boundary changes of 1974, and it still reads as a Berkshire village in the way its old houses cluster around the Upper Cross, a fifteenth-century stone cross that is listed Grade II*. Many of the houses nearby are timber-framed. The roofs above those frames are as individual as the walls beneath them, with their own lean, their own repairs and their own sags, and each one needs reading before a repair is planned. Two cottages side by side can need quite different treatment because of decisions made by owners a century ago.
Q1.1Why do old roofs sag, and is that a fault?
A dip along a ridge or a wave across a slope is often just age: heavy coverings, softened timbers and decades of settlement. It becomes a fault when the movement is recent, when rafters have split, or when the wall plate beneath has rotted from a leak nobody noticed. Looking at the ridge from the lane tells us part of the story, and a look inside the roof space tells us the rest. Daylight showing between slates or tiles from below is a sign of gaps, while dark, damp-stained rafters point to a slow leak that has been running for some time.
Q1.2When is a patch enough?
When the covering is mostly sound and the failure is local, a patch is the right call. A cracked tile, a lifted piece of lead or a few open joints in a chimney stack can be cured without opening the whole slope. Where battens have rotted across a wide area, patching only postpones the problem, and the honest advice is to re-cover that part properly. Our pitched roofing page explains how that choice is made.
One habit pays off on an old roof. Stand in the lane after the leaves have fallen and again after the worst of winter, and study the slopes through binoculars if you own a pair. Slipped tiles and missing pointing cost far less to deal with in the first month than in the fifth, and photographs taken then give the surveyor a starting record.