Rigid Foam Insulation Above The Roof Sheathing

Rigid insulation layers exterior to existing roof sheathing must provide sufficient thermal insulation r value to control condensation risk see climate specific guidance.

Rigid foam insulation above the roof sheathing.

This type of insulated roof assembly limits thermal bridging through rafters. In my local area there is a green building consultant that recommends a ci panel which is basically eps foam glued to osb. 1 inch and 2 inch thicknesses are common. Install nailbase for cladding.

Rigid foam insulation also known as insulating boards provide high r values. You can even place it under the foundation slab. Rigid insulation is one of the best tools to reduce your energy costs. Install it anywhere from the roof to the foundation.

Nail it around the edges with roofing nails. After installing several layers of rigid foam above the roof sheathing these workers installed plywood above the rigid foam. 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. The exposed edges of the 3 layers of rigid insulation are no longer exposed.

Nailbase must be vented in high snow load areas. Benefits of rigid foam on top of sheathing. Many homes in more urban areas or other places with dense populations are opting for this method because they can better optimize space. 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. Installing rigid foam insulation on top of roof sheathing is a great option for commercial buildings and homes with limited space. More insulation on the exterior is good. 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.

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 provides thermal protection and it can also serve as an air and moisture barrier. 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. Over the foam you will need something to nail the roofing to usually a solid sheet of plywood or osb.

The boards are available in several thicknesses and r values. The plywood was fastened through the rigid foam to the rafters with long screws. Install roofing underlayment flashing and cladding as per best practices.