Rigid Foam Above The Roof Sheathing

Rigid foam may shrink so some builders are wary of depending on the rigid foam to be your air barrier.

Rigid foam above the roof sheathing. Use rigid foam insulation to cover wider spans of roof sheathing between joists. How to retrofit a roof to a high performance roof with insulating sheathing above the roof deck plus cavity insulation in roof framing remove existing roofing and non adhered roof underlayment. Polyisocyanurate insulation above the sheathing and approximately 91 4 in. To save a step i would recommend using a nailbase panel foam preadhered to osb or sometimes plywood on one side only see photo facing page.

We live in zone 5 suburb of chicago and are hopefully about to put rigid foam above the roof sheathing on just the northeast roof portion of our roof. 3 benefits of rigid foam sheathing. The nailbase panels are installed with long screws that have flat heads. The main issue people encounter with insulation above sheathing is when it expands.

4 of polyiso under 4 of eps all above the original roof sheathing. Deck for a thick roof rigid foam insulation installed above the roof assembly can create an energy smart roof. Avoids nails or screws which could penetrate the metal roof and cause leaks. High moisture areas may benefit from leaving a small air space between roof sheathing and the rigid foam insulation panels.

Then a second layer of plywood sheathing and asphalt shingles following the steps explained in this article. Over the foam you will need something to nail the roofing to usually a solid sheet of plywood or osb. However for the best performance and for when space comes at a premium it s tough to beat rigid foam insulation. Apply a continuous air control membrane to existing roof sheathing or tape all joints between roof sheathing panels with an acrylic or butyl adhesive.

Nail it around the edges with roofing nails. Here is the controversy. With three layers of 11 2 in. 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.

Of cellulose insulation in the rafter cavities the roof shown here has an r value of approximately 63. Plywood has an r value of 1 25 and fiberglass batts have an r value of 3 14. Box beam gable framing new gable overhang is framed in the form of a box beam hanging off of a new layer of roof plywood roof sheathing cantilevered over the top of the 3 layers of rigid insulation. The exposed edges of the 3 layers of rigid insulation are no longer exposed.