As standard our bases have the U-value of 0,78! But we can produce them with even lower U-values , let us know what you need. And for the lids the U-value depends on what kind of material and how thick polycarbonate or how many layers of domes. So just let us know what U-value you need. Here comes our article numbers that can be specified on projects. Firstly our opening system with gas-springs ,fusible link + electrical magnet. All KlarVent in this size with gas-springs as opening system have TWO lids. This is with 300mm high standard base and covered aluminium lids: B1020-30-1-2-11. Then same base with multi-walled polycarbonate as lids. : B1020-30-30-2-11. And when you want a 500mm high base you only change the numbers to: B1020-50-1-2-11 (covered alu-lids). And B1020-50-30-2-11 (daylight lids). And for our special renovation base you just have the numbers: B1020-3R-1-2-11 (covered alu-lids) , or B1020-3R-30-2-11 (daylight lids). And on this size with electric motor as opening system they only have ONE lid. Here are the article numbers with motors and 300mm high base: B1020-30-1-1-31 (covered alu-lid). B1020-30-30-1-31 (daylight lid), if you want dome instead just add "dome" and how many layers. And with 500mm base + motor: B1020-50-1-1-31. (covered alu-lid). B1020-50-30-1-31 (daylight lid). And with our renovation base+ motor: B1020-3R-1-1-31 (covered alu-lid). B1020-3R-30-1-31 (daylight lid).