What does a survey of a stone roof look for?

The outside check works over each slope one course at a time. We look for slabs that have slipped, split or lost their face, and for the gaps and stains that show where water has been finding a way in. A slab that has crept down a few centimetres tells us its peg or nail has let go. A run of slabs dipping in a line suggests the batten under them has softened.

Edges and junctions get close attention. The verge is the finished edge at a gable end, the eaves are the bottom edge, and the ridge is the top. Each should sit firm and be bedded properly. We also note earlier repairs, because blobs of cement or hard mortar can show where somebody once tried to stop a leak in a hurry. A picture is taken of each fault, so the quote can point at evidence you have looked at yourself.

A great deal of the real evidence sits on the underside. From the loft we examine the back of the covering, the rafters and the battens for daylight, damp staining and soft or rotten timber. Daylight showing through the underside means a gap in the covering. A damp patch low on a rafter points to water that may have been running for years. Pressing a batten tells us at once whether it can still be trusted, and a probe into a doubtful rafter foot shows how far any softness runs.

The loft also shows whether an underlay is present, what state it is in and how the roof is ventilated. An old roof may have none, with the stone alone keeping out the weather, and that changes which repairs make sense. Our guide on repair, re-lay or replace a Horsham stone roof explains how these findings turn into a verdict.

Leaks on a stone roof often begin at a detail rather than in the middle of a slope. We inspect the lead flashings at chimneys and abutments, which are the strips of lead turned into the masonry where the roof butts against a chimney or gable. We inspect valleys, the lines where two slopes meet and water runs between them, and any lead soakers, the small folded sheets tucked beneath the slabs. Once a flashing lifts or splits, water finds its way behind the slabs.

Mortar comes next. A loose or crumbling ridge bed, or a hip held by old mortar alone, may need rebedding. The 2014 revision of BS 5534 expects a mechanical fixing at ridges and hips as well as the mortar bed. BSI adds that the standard might not suit certain old roofs laid with traditional or reclaimed materials, so we judge what suits the roof in front of us. Our guide on lime mortar on old roofs explains why the bedding matters.

On bats, GOV.UK is clear that every species, with its breeding sites and resting places, is fully protected by law, and re-covering a roof is among the jobs capable of disturbing them. Signs of roosting are noted in the loft and reported to you before any work is planned.

Access is the other practical point. The survey is done from ladders and from inside the loft, and a heavy stone roof is never walked across carelessly, because a slab can crack under a footfall. Where a complete inspection would need scaffold, the quote says so. Photographs are taken from places we can reach safely. Should water be coming in during the visit, stopping that comes ahead of everything else on the list, and the survey carries on once the immediate trouble is dealt with. The weather on the day can shape how much of the outside is seen close up.

Following the visit you receive photographs of your own roof, each fault shown as we found it, and, with it, a written quote carrying one overall price for the work recommended. The verdict leads: repair, re-lay or replace, and why. If the fault is small, the advice is to keep the fix small too.

You can also pay for an independent survey for a second view. Checkatrade lists £300 to £500 for a roof survey and around £210 for a drone survey, plus VAT, which can make sense if you are mid-purchase or need a record for the council. Keep the photographs, since they are the best evidence for a conservation officer or an insurer, and store copies somewhere other than your phone. Ask us to talk you through any picture that is unclear. Our Horsham stone roofing page and our answer on how long a Horsham stone roof lasts show what happens next.