Insulation Under Roof Sheathing

Water is insulation s enemy.

Insulation under roof sheathing.

It will help you to eliminate problems that may come when the house becomes extremely cold in the winter and terribly hot in the summer. T he problem with the insulation against the sheathing expands. At night it goes back through the foam to the osb. In warm climates zones 1 through 4 low density open cell spray foam insulation is the typical choice since it is vapor permeable and will allow drying of the exterior sheathing and roof framing if they happen to get wet via diffusion into the interior of the building.

The moisture is held in place by the insulation which allows for damage to the framing and other building components. Insulation is applied in direct contact with the underside of the structural roof sheathing. Apply a continuous air control membrane to existing roof sheathing or tape all joints between roof sheathing panels with an acrylic or butyl adhesive. How to retrofit a roof to a high performance roof with insulating sheathing above the roof deck plus cavity insulation in roof framing remove existing roofing and non adhered roof underlayment.

The attic or rafter assembly meets one of the following conditions regarding the air permeability of the insulation directly under the structural roof sheathing. If there is a roof leak the insulation will be damaged by the water leaving you with less insulating value. Polyurethane spray foam metal roof insulation. Avoids nails or screws which could penetrate the metal roof and cause leaks.

Cut each sheet to the desired size using a utility knife then fasten it in place using staples or adhesive. Use rigid foam insulation to cover wider spans of roof sheathing between joists. It hits the osb roof sheathing and keeps going through the foam into the attic air. In most climate zones requires a minimum r value of air impermeable insulation on or under the roof deck.

One possible failure mode is that open cell foam. In order to add moisture barrier under metal roof you can spray the undersides of the roof by using a thick layer of polyurethane spray foam. The problem arises with moisture. It creates a breeding ground for mold and mildew and ruins the air trapping pockets that block heat flow.

Box out light fixtures. There are at least two good reasons why this approach makes more sense than installing the insulation under the roof sheathing. There are lots of different ways to insulate this type of roof but one of the best methods calls for the installation of rigid foam insulation above the roof sheathing. The next day even more moisture is driven inward.

There have been isolated moisture related incidents that raise potential concerns about the overall hygrothermal performance of these systems.