Rigid Foam Insulation Above The Roof Sheathing

Install roofing underlayment flashing and cladding as per best practices.

Rigid foam insulation above the roof sheathing.

The way this is installed would be the osb to the exterior. Many homes in more urban areas or other places with dense populations are opting for this method because they can better optimize space. Nail it around the edges with roofing nails. The exposed edges of the 3 layers of rigid insulation are to be sealed with another layer of membrane.

Over the foam you will need something to nail the roofing to usually a solid sheet of plywood or osb. Rigid insulation sheathing is made of a rigid plastic foam that is typically sold in 4 8 or 4 10 foot boards. Benefits of rigid foam on top of sheathing. Installing rigid foam insulation on top of roof sheathing is a great option for commercial buildings and homes with limited space.

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. This type of insulated roof assembly limits thermal bridging through rafters. More insulation on the exterior is good. Rigid foam boards used in ceiling insulation are often made of either cellulose fiber fiberglass polystyrene or polyurethanes.

After installing several layers of rigid foam above the roof sheathing these workers installed plywood above the rigid foam. Install nailbase for cladding. Rigid insulation is one of the best tools to reduce your energy costs. Nailbase must be vented in high snow load areas.

The plywood was fastened through the rigid foam to the rafters with long screws. The exposed edges of the 3 layers of rigid insulation are no longer exposed. The boards are available in several thicknesses and r values. Rigid foam insulation also known as insulating boards provide high r values.

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. 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. Install it anywhere from the roof to the foundation. Rigid insulation provides thermal protection and it can also serve as an air and moisture barrier.

1 inch and 2 inch thicknesses are common. 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. Rigid insulation layers exterior to existing roof sheathing must provide sufficient thermal insulation r value to control condensation risk see climate specific guidance.