Wall Moisture Ingress Tomography

Water slows WiFi far more than dry wood or drywall does. Signals that cross a damp patch arrive a little late and a little weak; signals that miss it do not change at all. Comparing many crossing paths draws a picture of exactly where the wall is getting wet — days to weeks before your eyes could.

In the physics: Water (eps_r~80) vs dry drywall/timber (eps_r~2-4): even a few percent volumetric moisture raises the local permittivity, which (a) slows propagation through the wall — increasing the excess delay of transmitted/reflected multipath taps by tens of ps-to-ns, and (b) increases sigma, attenuating specific paths. Paths that geometrically intersect the wet zone change; others do not, giving spatial selectivity.