How To Install Rigid Foam On Top Of Roof Sheathing

A roof over a vented unconditioned attic does not need to include any insulation.

How to install rigid foam on top of roof sheathing.

Installed on the roof exterior foam makes the living space below more comfortable and reduces the likelihood of ice dams. Use the irc to determine foam thickness. 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.

If you choose to install rigid foam on top of your roof sheathing the foam has to be thick enough to keep the lower layer of roof sheathing above the dew point in the winter. If rigid foam sheathing is used on top of wood sheathing this doesn t matter. A vented attic is basically outdoors so installing rigid foam above your roof sheathing is a waste of money and a waste of rigid foam. This retrofit assembly is appropriate for homes with conditioned attics or where the retrofit is intended to create a conditioned attic.

If you have a vented attic it makes no sense to install rigid foam 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. 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. Remove existing roofing and non adhered underlayment to expose 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. Slightly more expensive adding a layer of rigid foam on top of plywood or osb sheathing will increase the cost of the project. How to install rigid foam on top of roof sheathing. Nail it around the edges with roofing nails.

The illustration shows two layers of osb or plywood roof sheathing. The exposed edges of the 3 layers of rigid insulation are no longer exposed. A lower layer conventionally nailed to the rafters and an upper layer installed as a nailing surface for the roofing material on top of the rigid foam. Install insulating sheathing above the roof deck on existing homes.

However most cathedral ceilings and. If the foam is too thin the roof sheathing will be cold which can lead to problems with condensation or moisture accumulation.