Finding rafters accurately is one of the most important steps when fixing anything to a roof — solar mounts, snow guards, structural anchors. Get it wrong and you risk missed fixings, rework, and wasted time.
Old methods (and why they frustrate installers)
- Loft access: useful when you can get in, but many roofs have limited access, insulation, or no safe walkway under the work.
- Tapping and probing: slow, subjective, and easy to misread on modern coverings.
- Removing tiles or slates: accurate but slow, messy, and often unnecessary.
- Stud finders: made for walls, not roofs — density and air gaps defeat them (see our dedicated guide).
Scan from outside on thin coverings like slate
The free Rafter Finder app uses the sensors already in your phone to detect rafter and batten nails through the covering. On thin coverings — natural slate, Cambrian, many fibre-cement products — you can scan straight off, no extra kit.
Step-by-step with the free app
- Place the phone flat on the tile or slate and wait for Ready / calibration.
- Slide steadily. When the indicator confirms a hit, you’ve found a rafter or batten nail.
- Find two or three hits in a vertical line to mark the rafter centreline.
- Mark, then fix — no tile removal needed just to locate the timber.
When the free app needs magnets
On thicker coverings (heavy slate, plain tiles, interlocking concrete), the rafter nail can sit beyond comfortable phone-sensor range. Place three neodymium magnets evenly spaced along each rafter from the loft (or known structure), then scan from outside. Space them out — don’t stack them. The free app still does the detection; the magnets bring the target closer to the sensor.
When Pro is the better tool
If you work every roof covering — thick concrete, stone, heavy slate, multi-layer — or you want AR rafter overlay and dedicated hardware, Pro & Sled is for that. Free is strong on thin coverings like slate. Pro is for every roof type.
Download the free app or register interest in Pro.