There are lots of different ways to insulate this type of roof but one of the best methods calls for the installation of rigid foam insulation above the roof sheathing.
Rigid foam insulation roof application.
This section outlines the conditions for unvented attic roof assemblies.
Nail it around the edges with roofing nails.
As far as cost and r value goes xps is the middle option of the three.
As the most used insulation type for roofing applications polyiso is a closed cell foam that is created by heating chemicals and synthetic materials into a composite material that cools into rigid foam panels.
Falls in the middle of the three types of rigid foam insulation in both cost and r value used most in walls or below grade applications recyclable and at about r 5 per inch costs around 42 per sq.
For a 1 in thick 4 8 panel comes unfaced or with a number of different plastic facings.
Insulated roof assemblies can be vented or unvented.
There are at least two good reasons why this approach makes more sense than installing the insulation under the roof sheathing.
This is the most easily recognized type of rigid foam insulation thanks to its popular blue green or pink color.
Start at the bottom of the roof and place the first piece of rigid foam insulation against the metal flashing starting at the center line.