The walls of old farmhouses were at least always halfway dry as long as vine or fruit trees on the house walls prospered. We already know that a vine/tree will dry the ground searching for water, so... put that green on the wall and let it pull water from there!
Climbing plants tend to have a drying effect on foundation walls, which in earlier times was a commonly used technique for the greening of buildings. For example, a single grapevine has to absorb and evaporate 500 liters of water to produce 1 kg of dry matter (which equates to about 2 kg of wood or 10 kg of fruit)! The widely branching surface roots will suck up all the rainwater first, while the deeper roots search for any lower lying soil water. If an area is drying out, the roots will atrophy there, and other roots will grow towards the nearest available moisture source.
