Spray Foam Insulation On Roof Sheathing

I m constructing a new home along the rhode island shore.

Spray foam insulation on roof sheathing.

The roofing materials are installed and consist of timberline shingles and full coverage ice and water barrier the entire roof. Open or closed cell spray foam is applied to the underside of the roof sheathing and additional fiberglass or cellulose insulation is blown in as a cost saving method for meeting high insulation requirements and filling in the cavity space between the rafters to the ceiling deck. There have been isolated moisture related incidents that raise potential concerns about the overall hygrothermal performance of these systems. Both papers basically came to the same conclusion.

Polyurethane or polystyrene spray foams can provide thorough coverage to roof rafters and attic walls in much less time than is needed for other materials. There are at least two good reasons why this approach makes more sense than installing the insulation under the roof sheathing. 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. Unvented roof strategies with open cell and closed cell spray polyurethane foam insulation sprayed to the underside of roof sheathing have been used since the mid 1990 s to provide durable and efficient building enclosures.

If you prefer to use closed cell spray foam nothing is preventing you from including a ventilated air space between the underside of your roof sheathing and the top side of your insulation. When installing attic insulation a case can be made for both radiant barrier sheathing with typical types of insulation as well as spray foam insulation. Insulated roof assemblies can be vented or unvented. Moisture from indoors can diffuse through the foam and find the cold roof sheathing where it accumulates and eventually rots the roof.

This can be accomplished by installing sturdy site built ventilation baffles in each rafter bay made for example by installing 1 x1 sticks and thin. Unlike solid insulation products that require careful measurement cutting and fitting spray foam can cover even the most uneven surface instantly. Open cell spray polyurethane foam ocspf or closed cell spray polyurethane foam ccspf insulation is sprayed along the underside of the roof sheathing to provide a unvented insulated and conditioned attic space or roof assembly that can be resilient durable and efficient in all climate zones. Radiant barrier sheathing is inexpensive and reflects thermal radiation to keep attic spaces cool.

Open cell spray foam insulation is risky in all climate zones we already know open cell spray foam is risky in cold climates. The movement of air into indirect conditioning of an unvented attic is a slow gradual process that will not be noticeable by occupants and typically will not put any strain on the hvac system.