[Greenbuilding] Unvented cathedral ceiling condensation

Sun Dec 11 14:49:32 CST 2016

Are we talking about air- or moisture-tight drywall? I guess I'd have
thought that taping the seams, never mind priming and painting, would take
care of the air permeability pretty well.

On Sun, Dec 11, 2016 at 9:19 AM, Michael O'Brien <obrien at hevanet.com> wrote:

> Hi, guys—
>
> Airtight drywall or ADA was originally based on an idea of Gus Handegord’s
> that was first implemented by Joe Lstiburek and his partner at the time.
> Their first trials used plywood to bridge between drywall sheets in back of
> framing junctions, and an acoustical sealant to seal drywall to framing.
> Since then it has developed into several different versions, but I would
> give them credit for starting it way back in the ancient 1980s.
>
> Best,
>
> Mike O'Brien
>
>
> On Dec 11, 2016, at 8:29 AM, Norbert Senf <norbert.senf at gmail.com> wrote:
>
> Here's one way:
>
> - strip off the tongue and groove.
> - Add a vapor barrier (6 mil poly). Research the proper details to seal
> the joints in the plastic. Here they use acoustical sealant.
> - a good way to handle wiring, etc. is to put 2x2 strapping on top, to
> provide a chase so you don't have to penetrate the plastic. It also avoids
> a gazillion nail holes in the plastic from the tongue and groove. The real
> pros will use acoustical sealant where the strapping is nailed to the
> rafters.
> - pay particular attention to all the edge details.
>
> There is another approach I have seen, which is airtight drywall. You need
> foil backed drywall, plus gaskets. I believe it was developed at the
> University of Illinois................Norbert
>
> On Sat, Dec 10, 2016 at 9:20 PM, Leslie Moyer <unschooler at lrec.org> wrote:
>
>> So it sounds like you're all pretty much in agreement that an air barrier
>> will fix the problem.  It seems to me that they have NO air barrier
>> now--good, bad or otherwise.  I.e. they don't have penetrations in their
>> air barrier--they don't HAVE an air barrier.  The layers in the
>> roof/ceiling assembly my friend describes below are the ENTIRETY of the
>> construction....he listed everything in order as it is. As far as vapor
>> movement goes, they are aware that the Roxul is not a vapor barrier and
>> neither is the tongue and groove ceiling. I was leaning toward a
>> "thermal bridging" problem & thought rigid foam insulation would fix
>> it...either under the boxcar siding or under the roof sheathing.
>>
>> There are no can lights in the ceiling.  There is wiring in place for one
>> fixture, I believe, but no other large holes.  I'm not sure, but I don't
>> think they have drywall under the tongue and groove boxcar siding on the
>> ceiling--he didn't mention it below and he didn't mention it in his
>> conversation with me earlier today.
>>
>> This is a brand new addition--unfinished still--and they are not looking
>> for a short-term fix. The builder just left and is willing to come back to
>> fix the problem now, but they need to come to an agreement about what that
>> "fix" will entail.
>>
>> So, for a solution, they need to air seal all holes of any size that go
>> from the sidewall plates up into the ceiling; air-seal all holes that
>> penetrate into the ceiling. Where, exactly, should the air barrier be
>> installed?  "The warm side" doesn't tell me enough--there are several
>> layers on the warm side.  They need to know if they should approach this by
>> removing the metal roofing & sheathing and go in from the top, or remove
>> the tongue and groove siding on the ceiling and fix things from the
>> inside-out.
>>
>> -Leslie Moyer
>>
>> --- obrien at hevanet.com wrote:
>>
>> From: "Michael O'Brien" <obrien at hevanet.com>
>> To: Green Building <greenbuilding at lists.bioenergylists.org>
>> Subject: Re: [Greenbuilding] Unvented cathedral ceiling condensation
>> Date: Sat, 10 Dec 2016 13:38:28 -0800
>>
>> Hi, Leslie—
>>
>> Just wanted to chime in to agree about the air leaks across the interior
>> side of the cathedral ceiling. Not only recessed can fixtures, but often
>> every wiring hole drilled through top plates, every vent stack and flue
>> have not been sealed to block air leaks. The walls may be contributing,
>> too, if there are penetrations in the top plates.
>>
>> The long-term fix is to take down the ceiling drywall so the leaks can be
>> sealed and a proper vapor rertarder installed, but in the short term they
>> could run a dehumidifier to reduce the water vapor in their occupied space.
>>
>> Sometimes builders will open up the blocks along the eaves and install
>> some sort of vent at or near the ridge, but this may have the effect of
>> sending cold air under the insulation and cooling down the interior surface
>> of the ceiling, it takes some detailing to keep the vent air above the
>> insulation.
>>
>> Best wishes,
>>
>> Mike O’Brien
>>
>>
>>
>> On Dec 10, 2016, at 11:50 AM, 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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