This extension set adds a 110 x 100cm tier to the matching grow rack. Every tier raises the height by 40.5cm. Inside you get the frame for one 110 x 100cm ebb and flow tray and four uprights. It uses 25 x 25 x 1.5mm aluminium tube with steel-reinforced corners, rated to 70kg per square metre.
There is no real limit to how high you go, beyond your ceiling. Each new tier multiplies your growing area on the same patch of floor. The frame supports also carry the lighting for the tier below. That keeps lamps tight to a canopy of leafy greens or herbs. Tray not included.