Insulate Unvented Roof

Insulating unvented roof assemblies.

Insulate unvented roof.

When hvac equipment is in the attic insulation and. Exterior insulation solves a lot of thermal nosebleeds but the amount of foam you put on the outside needs to be proportional with the amount of insulation on the inside within the rafter cavity. We agree that avoiding sheathing rot is critical and that air permeable insulation such as fiberglass or cellulose cannot be used alone. An unvented attic differs from a conventional vented attic in that there is no direct venting of the attic.

Unvented roof assemblies should be insulated either with air impermeable insulation rigid foam or spray polyurethane foam or with a combination of foam and air permeable insulation. Don t stay stuck in the sci fi nightmare of foam foam foam. We re big fans of fine homebuilding. Insulation and air barrier are applied directly to the underside of the roof deck are common in applications where designers are seeking cost effective and energy efficient roof assemblies.

In the most recent issue of fine homebuilding martin holladay wrote a piece on insulating unvented roof assemblies. Insulating the underside of roofs making the case for the unvented attic assembly background. Low slope and steep slope unvented roof systems i e. You need enough exterior foam to prevent condensation on the inside of the roof sheathing by keeping that plywood warm.

Four options for building an unvented roof assembly. Install insulation along the underside of the roof deck of an unvented attic rather than on the ceiling deck of a vented attic for either of two reasons. To provide an unvented conditioned space for locating hvac equipment in the attic and or to provide a continuous thermal barrier for designs that have complex coffered ceiling planes and or numerous penetrations for lights speakers vents soffits etc which make it difficult to achieve an airtight ceiling plane.