When skylights are installed, the area from the roof to the ceiling need to be properly insulated. This insulation is along the for perimeter of the skylight. Skylight shaft walls (the area between the roof to the ceiling around the perimeter of the skylight) should be insulated to the same R-value as other exterior walls if the attic they pass through is not insulated.
One option to consider, especially if several skylights are being installed, is to insulate the entire attic by spray foaming along the underside of the roofline, by installing rigid foam above the roof deck,
Please study the following pictures before reading further instructions
Please note the underlayment in the picture. Also, please not the rigid foam air barrier over the...