Unvented roof webinar - Why they may not work

[peakbagger]

I am subscribed to a site called Heatspring that covers sustainable energy and energy type construction. I took a couple of paid courses but some of the courses are free or sponsored. I got an invite on a seminar on why trying to insulated unvented roof spaces has the potential not to end well. I have seen and heard of many folks with Cathedral ceilings have problems. Its borderline technical on occasion but the pictures of how roofs go bad and the reasons why are great.

No charge to watch unless you need CEU credits for professional licensing. I need them for my license but great info. I will agree that once he gets to the graphs its probably time to go unless you are waiting for the quiz to get credits HeatSpring Magazine – Unvented Roofs Without Spray Foam: A New Free Course

 

[SpaceBus]

I've never seen anyone have a successful insulated "hot" roof.

 

[mcdougy]

Without taking the course....is a 2" minimum airspace and vented ridge the way to go?

 

[peakbagger]

If there is 2" space from soffit to ridge with a ridge vent, then its a vented roof which is the gold standard. This seminar covers roofs that are difficult to vent well like cathedral roofs or roofs with skylights and lots of gables.

 

[DickRussell]

The science behind how to build (and not build) a cathedral ceiling has been well understood for some time. Below are two links on the subject. Unfortunately, they can't be read in their entirety unless you pay for the GBA "Prime" level; they do have a trial period, though. Basically, you need a vented space above the insulation, closed cell foam of adequate R value right against the underside of the sheathing, or a rigid foam layer above the sheathing so as to keep the underside of the sheathing above the dew point. Exterior roof insulation (or wall insulation) must be of sufficient R value (usually 1/3 the total) relative to total R if there is interior insulation. Air sealing becomes crucial in such assemblies, as you don't want any interior air to be flowing through to contact the sheathing.

How to Build an Insulated Cathedral Ceiling - GreenBuildingAdvisor

Whether you decide to make it vented or unvented, get the details right — because every cathedral ceiling offers opportunities to make big mistakes

www.greenbuildingadvisor.com

Five Cathedral Ceilings That Work - GreenBuildingAdvisor

When GBA readers post questions about cathedral ceiling insulation, they are often directed to a 3,800-word article from 2011 called “How to Build an Insulated Cathedral Ceiling.” While the comprehensive […]

www.greenbuildingadvisor.com

 

[peakbagger]

If you watched the webinar, they agree with you. Their study is what happens if it not possible and that is the next best thing.