How To Install Rigid Foam On Top Of Roof Sheathing

Nail it around the edges with roofing nails.

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

Installing rigid foam insulation on top of roof sheathing is a great option for commercial buildings and homes with limited space. This retrofit assembly is appropriate for homes with conditioned attics or where the retrofit is intended to create a conditioned attic. How to install rigid foam on top of roof sheathing. 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 the foam is too thin the roof sheathing will be cold which can lead to problems with condensation or moisture accumulation. 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. 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. However if you want to use rigid foam in place of wood sheathing it needs additional bracing to prevent racking. Installed on the roof exterior foam makes the living space below more comfortable and reduces the likelihood of ice dams. If rigid foam sheathing is used on top of wood sheathing this doesn t matter.

Use the irc to determine foam thickness. A roof over a vented unconditioned attic does not need to include any insulation. However most cathedral ceilings and. You might as well put the rigid foam in the branches of a tree in your back yard.

Benefits of rigid foam on top of sheathing. Remove existing roofing and non adhered underlayment to expose roof sheathing.