Insulation Under Roof Sheathing

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.

Insulation under 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. One possible failure mode is that open cell foam. The moisture is held in place by the insulation which allows for damage to the framing and other building components. Cut each sheet to the desired size using a utility knife then fasten it in place using staples or adhesive.

Apply a continuous air control membrane to existing roof sheathing or tape all joints between roof sheathing panels with an acrylic or butyl adhesive. 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 attic or rafter assembly meets one of the following conditions regarding the air permeability of the insulation directly under the structural roof sheathing. Look for water stains on the roof sheathing or damp or moldy spots on attic joists and existing insulation as a clue to where leaks might be.

Unvented roof strategies with open cell and closed cell spray polyurethane foam insulation sprayed to the underside of roof sheathing have been used since the mid 1990 s to provide durable and efficient building enclosures. Water is insulation s enemy. At night it goes back through the foam to the osb. Insulated roof assemblies can be vented or unvented.

There have been isolated moisture related incidents that raise potential concerns about the overall hygrothermal performance of these systems. 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. The next day even more moisture is driven inward. If there is a roof leak the insulation will be damaged by the water leaving you with less insulating value.

There are at least two good reasons why this approach makes more sense than installing the insulation under the roof sheathing. It hits the osb roof sheathing and keeps going through the foam into the attic air. The problem arises with moisture. 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.

It creates a breeding ground for mold and mildew and ruins the air trapping pockets that block heat flow. Avoids nails or screws which could penetrate the metal roof and cause leaks. T he problem with the insulation against the sheathing expands. Use rigid foam insulation to cover wider spans of roof sheathing between joists.

Insulation is applied in direct contact with the underside of the structural roof sheathing.