The short answer
After six decades the weak points are rarely the tiles themselves. The old felt beneath them goes brittle, ridge and hip bedding crumbles, battens soften where moisture has got in, and flashings loosen. A survey separates a roof that needs a repair from one that needs stripping and re-covering.
The estate went up between 1957 and 1965, so most roofs here have had a long life already. The question to ask is not how old a roof is but how much of it is still doing its job.
Q1.1What fails first under the tiles?
Under the tiles, the original felt is the first part to give out. It was never meant to be seen again, and after sixty years of heat in the loft it can crack like old paper. Water then runs through a damaged tile and finds nothing to stop it. Ridges follow: the mortar that held the tiles has weathered away, and BS 5534 now expects them to be fixed mechanically as well as bedded. Around chimneys, mortar fillets and lead flashings dry out and pull free.
Q1.2Should the slope be patched or stripped?
Where the tiles are sound and the felt is damaged in only a few places, a local repair makes sense, because it is the least work that still cures the fault. If the felt is perished over most of a slope, patching just moves the leak. In that case the right answer is to strip the slope, fit new underlay and battens, and put the sound tiles back, topping up with matching ones. Our roof repairs page sets out what that looks like.
A roof built to the standards of the early 1960s will also have less insulation than a house built today. If a full re-cover is planned, it is the moment to ask what the roof will need under Part L, because it changes what building control expects.
We also look at the loft hatch and the eaves, because blocked eaves ventilation is a common reason for condensation that is mistaken for a leak. A roof that cannot breathe stains the underside of the felt and the timbers, and that can look worse than the fault really is.