The lines of lower level of snow in the photo are the lines of the wood structure below, in this case wood trusses. Building heat conducts through the wood to melt some of the snow on the roof above. The higher lines of snow are areas where below is attic air. This is typical with all wood stick framed buildings. There is a huge advantage to continuous, unbroken insulation layer. This is easily achievable by using Structural Insulated Panels (SIPs) to build new buildings. Contact us for more information.