Yes they are big thermal holes.
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.
Rigid foam above roof sheathing.
Four options for building an unvented roof assembly.
Dallas tx is located in a mixed humid climate region.
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.
With rigid foam above the sheathing and cellulose in the rafter cavities this roof is about r 63.
In unvented flat or low slope roofs with parapets perform a full flood test to ensure leak free installation of roofing membrane.
Polyisocyanurate insulation above the sheathing and approximately 91 4 in.
Test roofing membranes for integrity prior to covering from below.
That excess moisture ends up as drops of condensation on the roof.
Picture a cloud of moisture floating overhead between the rafters.
The three layers of foam help to seal air leaks but to make this assembly perform well you need to incorporate some unconventional details.
Figure 4 shows the potential for condensation of an unvented roof assembly in dallas tx.
Yes skylights went in.
With three layers of 11 2 in.
As it cools it can t hold as much moisture.
Martin s post focuses on the marketing of owens corning 039 s propink unvented attic insulation system.
Essentially condensation occurs at night when the temperature inside a building is warmer than outside.
Photograph 1 above left.
Original roof uninsulated rafter framing with board roof deck.
This roof assembly has no insulating sheathing installed above the roof deck.
Drying of unvented roofing assemblies is by definition only provided to the interior.
Rigid foam insulation installed above the roof assembly can create an energy smart roof.
Deck for a thick roof rigid foam insulation installed above the roof assembly can create an energy smart roof.
Of cellulose insulation in the rafter cavities the roof shown here has an r value of approximately 63.
Note that this roof assembly has rigid insulation installed above the roof deck in order to control the condensation potential.
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 rigid foam will be fairly thick see sidebar how much insulation.
Furring straightens out rafter plane for smooth plaster finish.
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.
Another approach is to build a cupola or ventilated doghouse in the middle of the low slope roof an approach championed by joe lstiburek.
