<div dir="ltr">Lstiburek rocks. Thank you for that article, Jeff.<br></div><div class="gmail_extra"><br><div class="gmail_quote">On Sun, Dec 11, 2016 at 7:58 AM, Jeff Martin <span dir="ltr"><<a href="mailto:jeff@open2learn.ca" target="_blank">jeff@open2learn.ca</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
<p>Leslie,</p>
<p>Adding an interior air barrier will almost certainly fix the
obvious problem of condensation running out of the ceiling and
down the walls, but it's still not great building science and,
unless detailed meticulously, may not be enough to avoid future
problems with moisture damage to the roof assembly. In addition to
the great GBA article that you've linked to, you might want to
check out this Joe Lstiburek article that appeared in Fine
Homebuilding a few years ago, to get a better understanding of
building science basics for roof ventilation:</p>
<p><a class="m_-7808219107655715282moz-txt-link-freetext" href="https://buildingscience.com/sites/default/files/migrate/pdf/PA_Crash_Course_Roof_Venting_FHB.pdf" target="_blank">https://buildingscience.com/<wbr>sites/default/files/migrate/<wbr>pdf/PA_Crash_Course_Roof_<wbr>Venting_FHB.pdf</a></p>
<p>If the chosen solution is to just try to achieve a better
interior air seal, rather than a more robust (and expensive)
solution of rebuilding the roof assembly so that it is either
properly vented (soffit and ridge vents, with baffles the full
length of the rafter bays) or uses a layer of impermeable
insulation to provide the air sealing and prevent moisture
build-up on the underside of the roof deck (e.g., 2 or 3 inches of
closed-cell spray foam on the underside of the roof deck), the
wood paneling will need to be removed from the ceiling and a good
quality membrane carefully installed on the underside of the
rafters, prior to reinstalling the t&g planks. Since you would
be relying on this membrane to do all the work of keeping moist
air away from the cold roof deck, I think you would want to use a
really good membrane, like Pro Clima INTELLO Plus. CertainTeed's
MemBrain is another option that's likely to cheaper and easier to
source, but we've found that it's somewhat fragile. In any case,
the membrane should installed using quality sealants and tapes,
and as per manufacturer recommendations. When reinstalling the
wood finish, care will need to be taken to minimize damage to the
membrane. If there are too many breaches in your air barrier, they
may lead to decay in the roof assembly that won't show up for
years.</p>
<p>That said, I think it would be more prudent to go for a more
robust solution, if budget allows. Pulling the Roxul and adding an
adequate layer of spray foam to the underside of the roof deck
would probably be the cheapest and least labor-intensive solution,
in this context. Considering your climate and the depth of the
rafter bays, it appears that 2" of closed-cell spray foam would be
adequate.</p><span class="HOEnZb"><font color="#888888">
<p>Jeff<br>
</p></font></span><div><div class="h5">
<br>
<div class="m_-7808219107655715282moz-cite-prefix">On 12/10/2016 9:20 PM, Leslie Moyer
wrote:<br>
</div>
<blockquote type="cite">
<div style="font-family:Arial,sans-serif;font-size:10pt">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. <span style="font-size:10pt">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. </span>
<div><span style="font-size:10pt"><br>
</span></div>
<div><span style="font-size:10pt">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.</span>
<div>
<div><br>
</div>
<div>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. <br>
<div><br>
</div>
<div>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. </div>
<div><br>
-Leslie Moyer<br>
<br>
--- <a class="m_-7808219107655715282moz-txt-link-abbreviated" href="mailto:obrien@hevanet.com" target="_blank">obrien@hevanet.com</a> wrote:<br>
<br>
From: "Michael O'Brien" <a class="m_-7808219107655715282moz-txt-link-rfc2396E" href="mailto:obrien@hevanet.com" target="_blank"><obrien@hevanet.com></a><br>
To: Green Building
<a class="m_-7808219107655715282moz-txt-link-rfc2396E" href="mailto:greenbuilding@lists.bioenergylists.org" target="_blank"><greenbuilding@lists.<wbr>bioenergylists.org></a><br>
Subject: Re: [Greenbuilding] Unvented cathedral ceiling
condensation<br>
Date: Sat, 10 Dec 2016 13:38:28 -0800<br>
<br>
Hi, Leslie—
<div><br>
</div>
<div>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. </div>
<div><br>
</div>
<div>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. </div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>Best wishes,</div>
<div><br>
</div>
<div>Mike O’Brien</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
<div>
<div>On Dec 10, 2016, at 11:50 AM, Leslie Moyer <<a href="mailto:unschooler@lrec.org" target="_blank">unschooler@lrec.org</a>>
wrote:</div>
<br>
<div>
<div style="font-family:Arial,sans-serif;font-size:10pt">
<div><span style="color:rgb(49,49,49);font-family:Roboto;font-size:16px;word-spacing:1px;background-color:rgb(255,255,255)">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! </span></div>
<div><span style="color:rgb(49,49,49);font-family:Roboto;font-size:16px;word-spacing:1px;background-color:rgb(255,255,255)"><br>
</span></div>
<div><span style="color:rgb(49,49,49);font-family:Roboto;font-size:16px;word-spacing:1px;background-color:rgb(255,255,255)">They read this article
& I think they will go ahead and pay to
read the article referenced within it: </span></div>
<div><span style="color:rgb(49,49,49);font-family:Roboto;font-size:16px;word-spacing:1px;background-color:rgb(255,255,255)"><br>
</span></div>
<span style="color:rgb(49,49,49);font-family:Roboto;font-size:16px;word-spacing:1px;background-color:rgb(255,255,255)">
<div><a href="http://www.greenbuildingadvisor.com/blogs/dept/musings/how-build-insulated-cathedral-ceiling" target="_blank">http://www.<wbr>greenbuildingadvisor.com/<wbr>blogs/dept/musings/how-build-<wbr>insulated-cathedral-ceiling</a></div>
<div><br>
</div>
<div>We are considered a "hot humid"
climate--NE Oklahoma </div>
…………………………….</span><br style="color:rgb(49,49,49);font-family:Roboto;font-size:16px;word-spacing:1px">
<br style="color:rgb(49,49,49);font-family:Roboto;font-size:16px;word-spacing:1px">
<span style="color:rgb(49,49,49);font-family:Roboto;font-size:16px;word-spacing:1px;background-color:rgb(255,255,255)">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.</span><br style="color:rgb(49,49,49);font-family:Roboto;font-size:16px;word-spacing:1px">
<br style="color:rgb(49,49,49);font-family:Roboto;font-size:16px;word-spacing:1px">
<span style="color:rgb(49,49,49);font-family:Roboto;font-size:16px;word-spacing:1px;background-color:rgb(255,255,255)">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.</span><br style="color:rgb(49,49,49);font-family:Roboto;font-size:16px;word-spacing:1px">
<br style="color:rgb(49,49,49);font-family:Roboto;font-size:16px;word-spacing:1px">
<span style="color:rgb(49,49,49);font-family:Roboto;font-size:16px;word-spacing:1px;background-color:rgb(255,255,255)">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!</span></div>
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