Unvented Shed Roof With Above Deck Installation

Yes skylights went in.

Unvented shed roof with above deck installation. Four options for building an unvented roof assembly. Test roofing membranes for integrity prior to covering from below. This roof assembly has no insulating sheathing installed above the roof deck. But a space needs to be a space or what is the point.

With three layers of 11 2 in. Note that this roof assembly has rigid insulation installed above the roof deck in order to control the condensation potential. As it cools it can t hold as much moisture. Photograph 1 above left.

Furring straightens out rafter plane for smooth plaster finish. In unvented flat or low slope roofs with parapets perform a full flood test to ensure leak free installation of roofing membrane. Rigid foam insulation installed above the roof assembly can create an energy smart roof. Essentially condensation occurs at night when the temperature inside a building is warmer than outside.

Original roof uninsulated rafter framing with board roof deck. Of cellulose insulation in the rafter cavities the roof shown here has an r value of approximately 63. Polyisocyanurate insulation above the sheathing and approximately 91 4 in. Another approach is to build a cupola or ventilated doghouse in the middle of the low slope roof an approach championed by joe lstiburek.

Deck for a thick roof rigid foam insulation installed above the roof assembly can create an energy smart roof. Figure 4 shows the potential for condensation of an unvented roof assembly in dallas tx. If the upper edge of a low slope shed roof intersects a vertical wall the most logical approach in my opinion is to detail the roof as an unvented roof. The three layers of foam help to seal air leaks but to make this assembly perform well you need to incorporate some unconventional details.

With rigid foam above the sheathing and cellulose in the rafter cavities this roof is about r 63. Yes they are big thermal holes. The rigid foam will be fairly thick see sidebar how much insulation. Drying of unvented roofing assemblies is by definition only provided to the interior.

Unvented roof diagram i know this is a very basic example so if you want to read more on the topic i ve put some additional reading for unvented roofs at the end of this article. Simply put unvented roofs get rid of the vents and move the thermal air control and moisture boundaries to the roof deck. Rigid foam above roof sheathing. That excess moisture ends up as drops of condensation on the roof.

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. Picture a cloud of moisture floating overhead between the rafters. Yes unvented roof assemblies can be insulated with fiberglass a wufi post and not just in climate zones 2b amp.