Take care of the insulation substance as homogeneous, While in serious apps, rigid materials have joints as well as cracks. So, the U-price is typically bigger than what It might be When the insulation behaved being a homogeneous material. Reference two offers direction on calculating U-values. It may be noticed https://banksy-art36995.pointblog.net/the-2-minute-rule-for-storm-windows-78897982