How To Install Rigid Foam On Top Of Roof Sheathing

However if you want to use rigid foam in place of wood sheathing it needs additional bracing to prevent racking.

How to install rigid foam on top of roof sheathing.

Remove existing roofing and non adhered underlayment to expose roof sheathing. Installed on the roof exterior foam makes the living space below more comfortable and reduces the likelihood of ice dams. A roof over a vented unconditioned attic does not need to include any insulation. If rigid foam sheathing is used on top of wood sheathing this doesn t matter.

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. Updated on december 15 2017 with information on the u factor alternative. 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. If you have a vented attic it makes no sense to install rigid foam above the roof sheathing.

You might as well put the rigid foam in the branches of a tree in your back yard. The exposed edges of the 3 layers of rigid insulation are no longer exposed. Install insulating sheathing above the roof deck on existing homes. Use the irc to determine foam thickness.

This retrofit assembly is appropriate for homes with conditioned attics or where the retrofit is intended to create a conditioned attic. 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. Benefits of rigid foam on top of sheathing. Slightly more expensive adding a layer of rigid foam on top of plywood or osb sheathing will increase the cost of the project.

Many homes in more urban areas or other places with dense populations are opting for this method because they can better optimize space. The illustration shows two layers of osb or plywood roof sheathing. 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. 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.

How to install rigid foam on top of roof sheathing. Nail it around the edges with roofing nails.