How To Insulate Non Vented Roof

Nail 1 furring along every rafter side against the roof deck.

How to insulate non vented roof. 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. Rigid foam insulation installed above the roof assembly can create an energy smart roof. Foam insulation can play an important role in both vented and un vented roof assemblies.

Spray foam with air permeable insulation. 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. 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.

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. 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. The vented roof also gives a path for moisture in the air whether from outside or inside the home to escape the roof structure. 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.

Air can move through the attic space freely and the floor of the attic is insulated to thermally separate the. As we note in our blog post yes unvented roof assemblies can be insulated with fiberglass a wufi post the building code written for the foam industry does ask for air impermeable insulation or foam. The typical vented roof has a vent at the lower eave and a vent at the higher. 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.

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. With rigid foam above the sheathing and cellulose in the rafter cavities this roof is about r 63. Because today we as an industry are insulating below the vented cavity as standard practice the building itself is no longer heating the cavity.