Retiling a pitched roof is the commonest large job on a British house, and it usually happens for a reason owners do not expect. The tiles are frequently fine. What has failed is the underlay beneath them, or the nails holding slates, or the battens, and those are only reachable by taking the covering off, which is why a roof can need stripping while every tile on it is sound.
Why a sound covering still gets stripped
Under a tiled roof from the middle of the last century is bitumen felt, which perishes, tears at the eaves and stops being a secondary barrier. Under a slate roof the slates were nailed, and the nails corrode long before the slate does, which is what nail sickness means and why slates start slipping in ones and twos. In both cases the covering is intact and the layer doing the real work is not, so the tiles come off, the underlay and battens are renewed, and the sound tiles go back on.
Reusing the covering, and when it works
Sound clay or concrete tiles and good slates can be reclaimed and relaid, which saves the material cost and adds sorting and handling labour. Expect a breakage allowance, because some will not survive removal. Reusing works best on plain tiles and slates and worst on old interlocking concrete tiles, whose profiles have changed over the decades so replacements for breakages are hard to match. Where reuse is proposed, ask what the allowance is and who pays if it is exceeded.
How long the work takes
A straightforward two storey semi is commonly around a week of working days, plus scaffold erection before and dismantling after. Add days for complex detail: valleys, dormers, chimneys and leadwork are slow. Add days for weather, since nobody strips a roof into a forecast of heavy rain and a part stripped roof is covered every night. A programme that promises a complete re-roof in two days is describing a different job than the one being sold.
Questions people ask about pitched roofing
Can a roof be retiled in sections?
Yes, and on a large or complicated roof it is normal, because it limits how much is open at once. It does mean the scaffold stays longer, which is a cost.
Is reslating cheaper than retiling?
Usually the reverse. Natural slate costs more per square metre than concrete tile and takes longer to lay, and reclaimed slate is priced as a material in its own right.
What happens if it rains mid job?
The exposed area is sheeted at the end of each working period and work stops. It is one of the reasons a fixed completion date on a roofing job is a hope rather than a commitment.