[Greenbuilding] Unvented cathedral ceiling condensation

[Norbert Senf]

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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