Find every rafterthrough the roof.

Stud finders, tapping, and probing are unreliable on slate — the covering is dense and there’s an air gap underneath. The free Rafter Finder app uses your phone’s sensors to find rafter and batten nails through thin slate, without taking tiles off. Scan along the batten (usually about a third of the way up the slate) to pick up the batten or rafter nail.

Not reliably. Most stud finders are made for walls. On a roof the air gap between the covering and the rafter throws them off. Rafter Finder is made for this job.

Yes, on thin coverings like natural slate and similar thin products. Phone only, works offline, free forever. If you need every roof covering — thicker tiles, concrete, stone, multi-layer — that’s what Pro & Sled is for.

Indicator 1 shows a LIVE reading. You’re looking for the local high. Always scan along the batten (usually about a third of the way up a slate) to find the batten or rafter nail. Two or three local highs in a vertical line — that’s the rafter.

Indicator 2 is a confidence indicator. Scan the area first so it can record the data, then the confidence bar hits 100% when it finds that area’s local high. Best when you already know roughly where the nail is and want to pin it down.

Calibration tells the app where the sensor is in your phone, so it can show the sensor’s position on screen while you scan.

Pro is for every roof covering. You get a dedicated sensor and a wheeled phone sled, 150× better resolution* than phone-only sensing, deeper nail detection, simpler calibration, and an AR overlay of the rafters. Planned at £329 a year with hardware included. Still in development — register interest if you want it. The free app remains best for thin coverings like slate. (*Targeting 166× — currently in development.)

Yes. On thin coverings like slate, scan from outside with the free app. On thicker roofs, Pro is meant to work from outside on every covering type. Magnets can still help the free app on some thicker jobs if you place them once from below, then scan outside.