How To Insulate Non Vented Roof

Rigid foam insulation installed above the roof assembly can create an energy smart roof.

How to insulate non vented roof.

Air can move through the attic space freely and the floor of the attic is insulated to thermally separate the. 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. Cut and insert 1 or thicker high r foam insulation sheets r 8 per inch against the furring giving a 1 or greater air path between the insulation and the roof deck under the cathedral ceiling. In an un vented roof foam can serve as the air barrier and vapor retarder and prevent moisture from getting in to the roof cavities.

A layer of spray polyurethane foam can be installed against the underside of the roof sheathing with the rest of the rafter cavity filled with air permeable insulation. The typical vented roof has a vent at the lower eave and a vent at the higher. Because today we as an industry are insulating below the vented cavity as standard practice the building itself is no longer heating the cavity. The three layers of foam help to seal air leaks but to make this assembly perform well you need to incorporate some unconventional details.

In this energy smart homes article senior editor martin holladay explains how to insulate a vented low slope shed roof using a combination of intake vents and cupolas. Foam insulation can play an important role in both vented and un vented roof assemblies. Preventing moisture is essential for having a properly functioning un vented roof. In a vented roof foam can seal the openings and serve as an air barrier and a vapor retarder in addition to its insulating function.

Nail 1 furring along every rafter side against the roof deck. The vented roof also gives a path for moisture in the air whether from outside or inside the home to escape the roof structure. If you re considering re roofing it might be wise to remove the existing insulation boxes from above the rafter beams and either install sips and leave the roof unvented or install ventilation baffles and a new roof deck and then insulate between the rafters with strapping and drwall. Vented roofs provide the capacity for moisture to be removed from the underside of roof sheathing via convection currents in the vent cavity.

You must meet the same minimum code requirements for the spray foam layer and the total assembly as for the rigid foam plus air permeable insulation approach. Because of limited space between the roof sheathing and ceiling joists a low slope shed roof can be difficult to insulate properly. Using intello plus with thermal insulation provides the necessary air and vapor barrier needed to prevent structural damage.