Insulate Tin Roof Without Decking

T he problem with the insulation against the sheathing expands.

Insulate tin roof without decking.

In this article we are going to explore both financial and technical aspects when it comes to looking for the best method to insulate the metal roofing. If you choose to omit the plywood from a residential construction install a vapor barrier between the purlins and the metal roof or plan to spray closed cell foam insulation between the rafters to eliminate the temperature differential between the air in the building and the metal. In warm climates zones 1 through 4 low density open cell spray foam insulation is the typical choice since it is vapor permeable and will allow drying of the exterior sheathing and roof framing if they happen to get wet via diffusion into the interior of the building. The problem arises with moisture.

First nail 1x2s to the rafter sides up against the roof strapping. You can install fiberglass insulation against the metal roof and prevent moisture problems if you cover it with a vapor barrier. This will provide an air space above the foam insulation to improve ventilation on the underside of the metal roofing. It is possible to insulate from below as you suggest with rigid polystyrene insulation.

The moisture is held in place by the insulation which allows for damage to the framing and other building components. If there is a roof leak the insulation will be damaged by the water leaving you with less insulating value. Some homeowners choose to use unfaced fiberglass insulation batts.