How long should a roof last?

Natural slate can remain serviceable for a very long time. Clay and concrete tiles are also durable. What wears out sooner is everything doing the holding and the sealing: nails, battens, underlay, mortar bedding at ridges and verges, and the flashings at every junction.

That is why a roof can look reasonable from the ground and still be close to the end of its useful life — and equally why a tired-looking roof sometimes has years left in it.

Fixing condition, because corroded nails release coverings one at a time across the whole roof. Batten and underlay condition, because they are the second line of defence. Detailing, because ridge, verge, valley and chimney junctions concentrate water. Exposure, because a roof taking sustained driven rain on one elevation ages unevenly.

Maintenance history matters too. A roof whose gutters and valleys have been kept clear has been protected from the most common cause of premature failure.

Figures quoted for materials describe the material under correct installation and reasonable maintenance. They say nothing about your fixings, your underlay, or how the details were formed on your roof. Two identical roofs built the same year can be decades apart in condition.

So a figure quoted for your roof by someone who has not seen it is a guess. What is worth having instead is a description of condition and what is likely to fail first.

An inspection that reports on fixings, bedding, flashings, valleys and drainage, with the roof space examined where it can be reached. Dated imagery of each elevation gives you a baseline you can compare against in a few years, which is what turns guesswork into planning.

Where the covering is sound but details are failing, targeted repairs may add many years. Where fixings are failing across the roof, renewal is a planned decision to budget for rather than an emergency to be surprised by.

The expensive version of roof ownership is discovering the position when water comes through a ceiling. The cheaper version is knowing the condition, keeping the drainage clear, repairing details as they fail, and budgeting for renewal when the evidence says it is due.

That is the practical value of knowing your roof's condition: it converts an unknown liability into a plan.