Rigid Insulation Over Roof Sheathing

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Rigid insulation over roof sheathing.

Rigid insulation provides thermal protection and it can also serve as an air and moisture barrier. There are at least two good reasons why this approach makes more sense than installing the insulation under the roof sheathing. Here s what you need to know about this growing trend. 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.

Next the rigid insulation can be installed. Fiberglass insulated walls opened up in the middle of the winter are often covered in a thin layer of frost on the interior side of the wall sheathing. First a single continuous membrane needs to be laid over the sheathing. Insulated roof assemblies can be vented or unvented.

The generic term is rigid foam sheathing or rigid foam insulation and it plays a direct role in a building s energy efficiency and performance. Rigid insulation layers exterior to existing roof sheathing must provide sufficient thermal insulation r value to control condensation risk see climate specific guidance. A roof over a vented unconditioned attic does not need to include any insulation. Once the sheathing has been exposed installation work can begin.

How to install rigid foam on top of roof sheathing. The boards are available in several thicknesses and r values. Johns manville r panel rigid roof insulation board offers r values of up to r 23 6 providing high thermal efficiency. 1 inch and 2 inch thicknesses are common.

The exposed edges of the 3. Install rigid insulation board in multiple layers with joints offset vertically and horizontally between adjacent layers. R panel is manufactured with a closed cell polyisocyanurate foam core bonded to fiberglass reinforced facers and designed for use over metal nailable and non nailable roof decks with a variety of membrane systems. One way to limit this is to keep the sheathing warm by adding a layer of rigid foam insulation.

Rigid insulation sheathing is made of a rigid plastic foam that is typically sold in 4 8 or 4 10 foot boards. Install nailbase for cladding. Updated on december 15 2017 with information on the u factor alternative. The glass fiber reinforcement contributes to improved fire performance and dimensional stability.

This acts as an air control and helps prevent the transfer of moisture from the sheathing into the rigid foam insulation. Outsulation is the construction practice of placing a layer of insulation on the exterior side of the building. Thermax sheathing is a non structural rigid board insulation consisting of a glass fiber infused polyisocyanurate foam core laminated between 1 0 mil smooth reflective aluminum facers on both sides.