Rigid Foam Insulation Above The Roof Sheathing

Over the foam you will need something to nail the roofing to usually a solid sheet of plywood or osb.

Rigid foam insulation above the roof sheathing.

Install it anywhere from the roof to the foundation. Rigid foam boards used in ceiling insulation are often made of either cellulose fiber fiberglass polystyrene or polyurethanes. Rigid insulation provides thermal protection and it can also serve as an air and moisture barrier. In my local area there is a green building consultant that recommends a ci panel which is basically eps foam glued to osb.

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. Rigid insulation layers exterior to existing roof sheathing must provide sufficient thermal insulation r value to control condensation risk see climate specific guidance. Rigid insulation is one of the best tools to reduce your energy costs. The exposed edges of the 3 layers of rigid insulation are no longer exposed.

Most local building codes require that rigid foam boards made from polyurethane or polystyrene be covered with a 15 minute fire rated thermal covering if they are used on the inside of the house. Installing rigid foam insulation on top of roof sheathing is a great option for commercial buildings and homes with limited space. Rigid foam insulation also known as insulating boards provide high r values. Benefits of rigid foam on top of sheathing.

After installing several layers of rigid foam above the roof sheathing these workers installed plywood above the rigid foam. 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. The way this is installed would be the osb to the exterior. Almost every house i see with exterior rigid foam in my online wonderings is covered with blue and pink xps the osb sheathing is nailed directly to the studs and is completely covered with the rigid foam.

Install nailbase for cladding. 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. You can even place it under the foundation slab. This type of insulated roof assembly limits thermal bridging through rafters.

Rigid insulation sheathing is made of a rigid plastic foam that is typically sold in 4 8 or 4 10 foot boards. Nail it around the edges with roofing nails. Install roofing underlayment flashing and cladding as per best practices. The exposed edges of the 3 layers of rigid insulation are to be sealed with another layer of membrane.

The boards are available in several thicknesses and r values. 1 inch and 2 inch thicknesses are common. More insulation on the exterior is good.