[Greenbuilding] Unvented cathedral ceiling condensation

Norbert Senf norbert.senf at gmail.com
Sat Dec 10 15:44:10 MST 2016


We call it a vapour barrier, because normally it is 6 mil special poly. But
actually, it is the air seal that is doing the work. Bulk air movement is
the issue. Vapor diffusion is a very minor concern..........N

On Sat, Dec 10, 2016 at 3:56 PM, Jason Holstine <jason at amicusgreen.com>
wrote:

> 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 <(819)%20647-5092>
> www.heatkit.com
>
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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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