Insulate Unvented Roof

If you don t want to use sips or nailbase there are four basic approaches.

Insulate unvented roof.

Four options for building an unvented roof assembly. Advantages of unvented attic assemblies. 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. You need enough exterior foam to prevent condensation on the inside of the roof sheathing by keeping that plywood warm.

When hvac equipment is in the attic insulation and. Insulating the underside of roofs making the case for the unvented attic assembly background. Don t stay stuck in the sci fi nightmare of foam foam foam. 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.

An unvented attic differs from a conventional vented attic in that there is no direct venting of the attic. Low slope and steep slope unvented roof systems i e. We re big fans of fine homebuilding. 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.

We agree that avoiding sheathing rot is critical and that air permeable insulation such as fiberglass or cellulose cannot be used alone. In the most recent issue of fine homebuilding martin holladay wrote a piece on insulating unvented roof assemblies. However architects of these compact roof assemblies must consider vapor permeance and arrangement of the materials to produce acceptable hygrothermal performance and low risk of condensation in the resulting conditioned attic space.