Rigid Foam Insulation Above The Roof Sheathing

You can even place it under the foundation slab.

Rigid foam insulation above the roof sheathing.

Many homes in more urban areas or other places with dense populations are opting for this method because they can better optimize space. Over the foam you will need something to nail the roofing to usually a solid sheet of plywood or osb. 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. The boards are available in several thicknesses and r values.

In my local area there is a green building consultant that recommends a ci panel which is basically eps foam glued to osb. Rigid insulation layers exterior to existing roof sheathing must provide sufficient thermal insulation r value to control condensation risk see climate specific guidance. This type of insulated roof assembly limits thermal bridging through rafters. Nail it around the edges with roofing nails.

Rigid insulation sheathing is made of a rigid plastic foam that is typically sold in 4 8 or 4 10 foot boards. Install roofing underlayment flashing and cladding as per best practices. Install it anywhere from the roof to the foundation. The exposed edges of the 3 layers of rigid insulation are no longer exposed.

Install nailbase for cladding. Rigid foam insulation also known as insulating boards provide high r values. Rigid foam boards used in ceiling insulation are often made of either cellulose fiber fiberglass polystyrene or polyurethanes. 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.

Rigid insulation provides thermal protection and it can also serve as an air and moisture barrier. Nailbase must be vented in high snow load areas. 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. Rigid insulation is one of the best tools to reduce your energy costs.

1 inch and 2 inch thicknesses are common. After installing several layers of rigid foam above the roof sheathing these workers installed plywood above the rigid foam. More insulation on the exterior is good. The exposed edges of the 3 layers of rigid insulation are to be sealed with another layer of membrane.

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. The plywood was fastened through the rigid foam to the rafters with long screws.