Rigid Foam Insulation Above The Roof Sheathing

Rigid insulation sheathing is made of a rigid plastic foam that is typically sold in 4 8 or 4 10 foot boards.

Rigid foam insulation above the roof sheathing.

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. Nail it around the edges with roofing nails. The plywood was fastened through the rigid foam to the rafters with long screws. Rigid foam boards used in ceiling insulation are often made of either cellulose fiber fiberglass polystyrene or polyurethanes.

Install it anywhere from the roof to the foundation. Installing rigid foam insulation on top of roof sheathing is a great option for commercial buildings and homes with limited space. Nailbase must be vented in high snow load areas. 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. Rigid foam insulation also known as insulating boards provide high r values. Install roofing underlayment flashing and cladding as per best practices. 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.

Rigid insulation layers exterior to existing roof sheathing must provide sufficient thermal insulation r value to control condensation risk see climate specific guidance. 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. Over the foam you will need something to nail the roofing to usually a solid sheet of plywood or osb. Benefits of rigid foam on top of sheathing.

Rigid insulation is one of the best tools to reduce your energy costs. 1 inch and 2 inch thicknesses are common. The exposed edges of the 3 layers of rigid insulation are to be sealed with another layer of membrane. Many homes in more urban areas or other places with dense populations are opting for this method because they can better optimize space.

Install nailbase for cladding. The exposed edges of the 3 layers of rigid insulation are no longer exposed. The way this is installed would be the osb to the exterior. In my local area there is a green building consultant that recommends a ci panel which is basically eps foam glued to osb.

More insulation on the exterior is good. Rigid insulation provides thermal protection and it can also serve as an air and moisture barrier. This type of insulated roof assembly limits thermal bridging through rafters.