How To Install Rigid Foam On Top Of Roof Sheathing

If rigid foam sheathing is used on top of wood sheathing this doesn t matter.

How to install rigid foam on top of roof sheathing.

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. 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. Installing rigid foam insulation on top of roof sheathing is a great option for commercial buildings and homes with limited space.

A roof over a vented unconditioned attic does not need to include any insulation. Many homes in more urban areas or other places with dense populations are opting for this method because they can better optimize space. You might as well put the rigid foam in the branches of a tree in your back yard. The illustration shows two layers of osb or plywood roof sheathing.

Benefits of rigid foam on top of sheathing. However if you want to use rigid foam in place of wood sheathing it needs additional bracing to prevent racking. Nail it around the edges with roofing nails. 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.

Use the irc to determine foam thickness. 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. However most cathedral ceilings and.

The exposed edges of the 3 layers of rigid insulation are no longer exposed. Install insulating sheathing above the roof deck on existing homes. 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. Installed on the roof exterior foam makes the living space below more comfortable and reduces the likelihood of ice dams.

Updated on december 15 2017 with information on the u factor alternative. Remove existing roofing and non adhered underlayment to expose roof sheathing.