Grandio Greenhouse Extension KitDESCRIPTION Kits can be used to expand to all 2015 and newer Grandio greenhouse models. Roof window is included. see detail below Element This 4 foot extension will add 24 square feet to your favorite growing space 10mm Polycarbonate panel and 1 Roof window included. Ascent 4' Extension: this will add 32 square feet to your favorite growing space. 6mm Polycarbonate panel and 1 roof window included 8' Extension: this will add 64 square feet to your