Unvented Shed Roof With Above Deck Installation

Furring straightens out rafter plane for smooth plaster finish.

Unvented shed roof with above deck installation.

Simply put unvented roofs get rid of the vents and move the thermal air control and moisture boundaries to the roof deck. This roof assembly has no insulating sheathing installed above the roof deck. That excess moisture ends up as drops of condensation on the roof. Another approach is to build a cupola or ventilated doghouse in the middle of the low slope roof an approach championed by joe lstiburek.

Test roofing membranes for integrity prior to covering from below. Note that this roof assembly has rigid insulation installed above the roof deck in order to control the condensation potential. Dallas tx is located in a mixed humid climate region. Yes skylights went in.

Original roof uninsulated rafter framing with board roof deck. Drying of unvented roofing assemblies is by definition only provided to the interior. Figure 4 shows the potential for condensation of an unvented roof assembly in dallas tx. Warm wet air rises and meets the cold roof and cools.

Polyisocyanurate insulation above the sheathing and approximately 91 4 in. Yes unvented roof assemblies can be insulated with fiberglass a wufi post and not just in climate zones 2b amp. The three layers of foam help to seal air leaks but to make this assembly perform well you need to incorporate some unconventional details. You can install all of the insulation above the roof sheathing but the foam has to be thick enough to meet minimum code requirements for ceiling r value.

Photograph 1 above left. But a space needs to be a space or what is the point. Rigid foam above roof sheathing. Picture a cloud of moisture floating overhead between the rafters.

Essentially condensation occurs at night when the temperature inside a building is warmer than outside. Yes they are big thermal holes. With three layers of 11 2 in. Four options for building an unvented roof assembly.

The rigid foam will be fairly thick see sidebar how much insulation. In unvented flat or low slope roofs with parapets perform a full flood test to ensure leak free installation of roofing membrane. Of cellulose insulation in the rafter cavities the roof shown here has an r value of approximately 63. As it cools it can t hold as much moisture.

With rigid foam above the sheathing and cellulose in the rafter cavities this roof is about r 63. Deck for a thick roof rigid foam insulation installed above the roof assembly can create an energy smart roof. Rigid foam insulation installed above the roof assembly can create an energy smart roof.