[Greenbuilding] Unvented cathedral ceiling condensation

[Jason Holstine]

Vapor barrier or simply an air seal?

 

 

From: Greenbuilding <greenbuilding-bounces at lists.bioenergylists.org> on behalf of Norbert Senf <norbert.senf at gmail.com>
Reply-To: Green Building <greenbuilding at lists.bioenergylists.org>
Date: Saturday, December 10, 2016 at 3:26 PM
To: Green Building <greenbuilding at lists.bioenergylists.org>
Subject: Re: [Greenbuilding] Unvented cathedral ceiling condensation

 

I'm guessing no decent vapor barrier detail on the warm side. The house acts like a chimney in cold weather, with the highest positive pressure at the cathedral ceiling. Air is going through the Roxul and hitting the bottom of the roof and condensing. Very commonly,  a poorly detailed pot light will do this. In southern climes where they are not used to airtight construction, it would be very unusual for somebody to know how to properly vapor barrier a pot light in a cathedral ceiling..................Norbert

 

On Sat, Dec 10, 2016 at 2:50 PM, Leslie Moyer <unschooler at lrec.org> wrote:

I have some nearby friends having a problem. I think I understand what the problem is, and even some possible ways to solve it, but I'm not certain I could give them advice that would fix their problem the best or cheapest way. I thought you guys could, though!  



They read this article & I think they will go ahead and pay to read the article referenced within it: 



http://www.greenbuildingadvisor.com/blogs/dept/musings/how-build-insulated-cathedral-ceiling

 

We are considered a "hot humid" climate--NE Oklahoma 

…………………………….

We have a question regarding condensation problems in a cathedral ceiling.  We live in northeastern Oklahoma (zone 3) and just added a dinning room (cathedral ceiling) 15 x 19 addition.  The addition was just opened up to the main house earlier this week, and we got hit with (what are for us) very cold temperatures.  Thursday night had a low of 12 F.  By noon on Friday we noticed that water was dripping down the north side interior wall  (along the drywall).  The drip lines appeared to be spaced every 24 inches, or about where a roof rafter would be.

The ceiling/roof construction was constructed with 2 x 8 rafters and insulated with R30 Roxul (rock wool) insulation and is not vented.  The interior ceiling is wooden tongue and groove car siding.   The roof decking is LP TechShield Radiant Barrier (with the metal foil side facing the interior of the house, as described on the boards) with a metal roof (there is felt paper in between the decking and the metal roof on the North side, but on the South side we used double bubble).   We did not have any condensation issues on the south wall.

We have spoken with over half a dozen different experts, and we’re getting as many different suggested solutions.  We are desperate to fix this problem and would greatly appreciate any help!  Thank you!


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-- 

Norbert Senf
Masonry Stove Builders
25 Brouse Road, RR 5
Shawville Québec J0X 2Y0
819.647.5092
www.heatkit.com

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