[Greenbuilding] Unvented cathedral ceiling condensation

Michael O'Brien obrien at hevanet.com
Sun Dec 11 16:19:21 MST 2016


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 <mailto: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 <mailto: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 <mailto: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 <mailto:obrien at hevanet.com> wrote:

From: "Michael O'Brien" <obrien at hevanet.com <mailto:obrien at hevanet.com>>
To: Green Building <greenbuilding at lists.bioenergylists.org <mailto: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 <mailto: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 <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!
_______________________________________________
Greenbuilding mailing list
to Send a Message to the list, use the email address
Greenbuilding at bioenergylists.org <mailto:Greenbuilding at bioenergylists.org>

to UNSUBSCRIBE or Change your List Settings use the web page
http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org <http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org>
_______________________________________________ Greenbuilding mailing list to Send a Message to the list, use the email address Greenbuilding at bioenergylists.org <http://eonapps/ft/wm/page/compose?send_to=Greenbuilding%40bioenergylists.org> to UNSUBSCRIBE or Change your List Settings use the web page http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org <http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org>
_______________________________________________
Greenbuilding mailing list
to Send a Message to the list, use the email address
Greenbuilding at bioenergylists.org <mailto:Greenbuilding at bioenergylists.org>

to UNSUBSCRIBE or Change your List Settings use the web page
http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org <http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org>



-- 
Norbert Senf
Masonry Stove Builders
25 Brouse Road, RR 5
Shawville Québec J0X 2Y0
819.647.5092 <tel:(819)%20647-5092>
www.heatkit.com <http://www.heatkit.com/>_______________________________________________
Greenbuilding mailing list
to Send a Message to the list, use the email address
Greenbuilding at bioenergylists.org <mailto:Greenbuilding at bioenergylists.org>

to UNSUBSCRIBE or Change your List Settings use the web page
http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org <http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org>

_______________________________________________
Greenbuilding mailing list
to Send a Message to the list, use the email address
Greenbuilding at bioenergylists.org <mailto:Greenbuilding at bioenergylists.org>

to UNSUBSCRIBE or Change your List Settings use the web page
http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org <http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org>

_______________________________________________
Greenbuilding mailing list
to Send a Message to the list, use the email address
Greenbuilding at bioenergylists.org

to UNSUBSCRIBE or Change your List Settings use the web page
http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/greenbuilding_lists.bioenergylists.org/attachments/20161211/502cb8ba/attachment.html>


More information about the Greenbuilding mailing list