Need to know the U-value by using 100mm thk IKO ALU insulation between roof joists 50×175 felt flat roof + 25mm insulation under side cold deck It’ll achieve around 0.22w/m2k based on the info provided. I’m building a retaining wall and would like to tank the load side. I’m not sure whether to use the IKO Hyload 1000SA or IKO Hyload 2000SA? What is the thinnest insulation board you offer for below under floor heating, whilst meeting the necessary insulation properties. I will be putting it on top of a 100 mm reinforced concrete slab.