Can a drone inspect chimneys, valleys and flashings?

Brickwork condition, pointing, spalling, haunching around the pots, pot condition and alignment, any cracking, and how the stack meets the roof. Stacks are exposed on every side and take weather from all directions, which is why they feature so heavily in leak diagnosis.

A stack leaning or with washed-out haunching is a safety matter as well as a weathertightness one.

Lining condition, whether debris or growth is restricting flow, whether coverings at the edges have slipped, and whether the valley has adequate capacity for what drains into it. Blocked valleys push water sideways beneath the coverings, which produces leaks well away from the valley itself.

Hidden and box gutter valleys are exactly the places nobody sees from the ground.

Whether lead or other metalwork has lifted at the top edge, corroded, split, or been formed badly — too short an upstand, insufficient lap, cement fillets in place of proper detailing. All of these are visible at close range.

What is not visible is the depth of the chase or the state of the fixing within the brickwork, which sometimes matters and needs physical inspection.

Detail failures are usually repairable locally, which is good news: a re-formed flashing or re-bedded valley edge costs far less than any covering renewal. Identifying them early is what keeps them local.

Where imagery and internal evidence agree, the repair can be specified with confidence.

Chimneys, valleys and flashings fail gradually, and the early stages — a slightly lifted flashing edge, a valley starting to silt up — rarely produce a leak straight away. Recording their condition before that happens is what allows a small repair rather than an emergency one.

Because these junctions concentrate water from a wider area of roof, a defect here tends to progress faster than a similar defect on an open slope, which is the practical reason they are worth checking on a schedule rather than waiting for a symptom.