[Greenbuilding] Unvented cathedral ceiling condensation

Sun Dec 11 19:17:47 CST 2016

Around the perimeter? Indeed.

On Sun, Dec 11, 2016 at 3:19 PM, Michael O'Brien <obrien at hevanet.com> wrote:

> Hi, Reuben—
>
> There is a small gap between the drywall and the framing, which, when you
> think about it, can be hundreds of feet long. So for example, air will flow
> between drywall and sole plate at floor level, and rise inside the wall
> cavity. Same with all the penetrations for light fixtures, electrical
> switch and outlet boxes. It can add up, but it’s easy to seal during
> installation.
>
> Best,
>
> Mike
>
>
> On Dec 11, 2016, at 12:49 PM, Reuben Deumling <9watts at gmail.com> wrote:
>
> 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-b
>>> uild-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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