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.

Rigid foam above the roof sheathing.

The purpose of the requirement that rigid foam installed above roof sheathing meet certain minimum r values is to ensure that the roof sheathing stays warm enough during the winter to avoid moisture accumulation and possible sheathing rot. If the sheathing is on the exterior of the foam then drying isn t a concern because interior vapor will never reach the sheathing and the sheathing will always dry to the exterior especially with any rainscreen. Rigid insulation sheathing is made of a rigid plastic foam that is typically sold in 4 8 or 4 10 foot boards. 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.

Polyiso consists of a uniform closed cell polyisocyanurate foam core and provides one of the highest r values per inch of any rigid insulation. Benefits of rigid foam on top of sheathing. Rigid foam sheathing is a form of insulation continuous insulation to be exact that s applied to the exterior of the building. Go back and check out photograph 10.

This was then foamed to complete the air seal. The nailbase panels are installed with long screws that have flat heads. Over the foam you will need something to nail the roofing to usually a solid sheet of plywood or osb. Apply a continuous air control membrane to existing roof sheathing or tape all joints between roof sheathing panels with an acrylic or butyl adhesive.

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. Johns manville polyiso foam sheathing insulation boards provide a continuous layer of insulation to reduce thermal bridging and improve energy efficiency. Installing rigid foam insulation on top of roof sheathing is a great option for commercial buildings and homes with limited space.