On outdoor walls, the higher up you go, the windier the conditions tend to be, and you will get more evaporative drying. To compensate for this additional loss, adjust to run the irrigation longer on the upper zones. You can expect to lose about ½ PSI of pressure per each foot of elevation. This corresponds to about ½ PSI for each tier of the LiveWall system and on very tall walls, booster pumps may be needed to sustain pressure. Plumbing should be sized and engineered accordingly.