People often ask for a patch because they hope it is the cheaper route. Sometimes it is. Sometimes it only moves the leak a metre along the slope, and the second visit costs more than doing the job properly in the first place.
Q2.1Which faults can be mended without re-tiling?
Two or three cracked tiles, a short length of damaged ridge, lead that has peeled back at a chimney or a valley full of moss can each be dealt with locally. If the battens are firm and the underlay behind them is intact, swapping individual tiles and refixing the ridge is sound, lasting work. We propose just enough work to cure the fault, and the quote says so.
Q2.2How do I know it is time to strip the slope?
Tiles can last a long time, but the fixings behind them often do not. Nails corrode, battens soften and underlay turns brittle. Once that has spread across a slope, new tiles on old battens are a false economy. Strip back the slope, put new battens and underlay on, and lay the good tiles again with a few matching extras. Concrete tiles are often put at around 30 to 60 years, clay longer, though a lifespan is a range for a decent roof and never a promise.
Extensions follow the same reasoning. A porch or kitchen roof that keeps leaking is often better renewed than patched yet again, and our flat roofing page explains the choices.
If a stripped roof turns out to belong to a listed building, the work is agreed with the council first, and nothing is thrown away that can be reused. Old tiles that are still sound often go back on the slope facing the lane, where they are seen, while newer matching ones go on the back. Sorting them on the ground, by size and by weathering, takes time, and it is the part of the job that decides how the finished roof looks from the road.