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Why is there mold on the cathedral ceiling?

SWQPjprdkG | Posted in Energy, Heating & Insulation on June 8, 2010 02:25am

I have a customer on the eastern shore of MD. They spend the winter away from here and the house is closed up. 3-4 years ago they had a remodel done which included batt insulating and drywalling a cathedral ceiling and a new roof. As they entered the home this season they found black mold on the cathedral ceiling.

They believe that when the work was done 3-4 years ago that a ridge vent was installed but no soffit vents and no baffles between the ratfters and  with the particularly bad winter we had that ice dams formed and somehow moisture got in the bays and trapped and caused mold and ruined insulation. This mold is at the flattened section near the peak of this ceiling.

After further discusssion I learned that their sump pump had failed also and that the area of the crawl space below the cathedral ceiling is without a vapor barrier. I believe that the failed sump punp and lack of vapor barrier is a more likely cause of this mold.

comments please!!

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  1. JAGQueen | Jun 08, 2010 03:52pm | #1

    Eastern Shore memories...

    Reminds me of visiting the Eastern shore.  Had a Girlfriend that had grandparents on Chincoteague.  We used to visit four or five times a year.

    But more to the point, they also always had mold problems.  Even in winter.  I would recommend looking at the sump first.  If the water rose and was not immetdiately drained, the humidity inside the house would have climbed a great deal.  Then the moisture barrier would be a detriment, keeping the moisture in.

    I remembered that the grandparents used to have mold problems with drywall even when there was no water.  Just because they had window units that would not really dehumidify the house.  I watched them try anti-mold paint and all sorts of other treatments over the 4 years we dated, all to no avail.  They ended up covering most of it with paneling, which I am sure was pretty unhealthy.  But the germ of the problem was that they did not have moisture barriers or vents or other new features.  They just had heat and lots of humidity, which the eastern shore has in abundance.

    So, I would recommend doing the crawl space treatment that they recommend at

    https://www.finehomebuilding.com/how-to/articles/built-wrong-from-start.aspx?ac=fp

    And then, when you put the drywall back up, use Densarmor drywall.  http://www.gp.com/build/product.aspx?pid=4659

    Heath

  2. DanH | Jun 08, 2010 09:27pm | #2

    The cause of the mold is the cathedral ceiling.  Even in the best of circumstances they're iffy, and it sounds like this one was poorly finished off.  Cathedral ceilings seem like a good idea until they start causing problems like this.

    The ridge vent does no good without soffit vents and baffles.

    (Of course, a wet crawl and failed sump pump don't help either.)

  3. Clewless1 | Jun 09, 2010 09:07am | #3

    Damage from ice damming? Not likely since the mold is up high. Your sump pump failure probably contributed to significant levels of RH in the house ... and a cool house when they were away and the possible thermal stack affect resulted in the moist air rising to the highpoints where it condensed. May be a clue to a poor insulation job as well. The moist air will condense on the coldest surfaces. Seems like I've most frequently seen mold down low on walls and particularly in closets (where there is little air flow near the walls).

    My money is on the sump failure as the primary culprit of the mold, though. Water in the crawl is a real issue.

    1. DanH | Jun 09, 2010 08:37pm | #5

      I suspect what happened is that the ridge vent and poor insulation made the very top of the ceiling very cold.  Warm moist air from inside the house (with wet crawl and failed sump) condensed on the cold ceiling.  Combination of factors.

      1. Clewless1 | Jun 10, 2010 08:07am | #7

        You're right ... combination of factors providing the perfect storm so to speak. I'm guessing the ceiling defficiencies alone may not have resulted in moisture/condensation. The sump problem tipped it over the scales.

  4. Scott | Jun 09, 2010 03:09pm | #4

    I'm thinking it's from condensation at the ridge. Was a vapor barrier properly installed in the ceiling?

    1. DanH | Jun 09, 2010 08:39pm | #6

      Vapor barrier in the ceiling would have done no good if it's condensation against the ceiling itself. 

      1. Scott | Jun 11, 2010 01:17am | #9

        >>>Vapor barrier in the

        >>>Vapor barrier in the ceiling would have done no good if it's condensation against the ceiling itself

        I'm not thinking th mold is from condensation on the ceiling itself; I'm wondering if the mold is coming through the drywall from behind.

        That is, if there is no vapor barrier, moisture is condensing on the exterior roof substrate, dripping on and through the insulation, and into the drywall.

        To the OP... does it look like the drywall has been made damp from behind?

        1. DanH | Jun 11, 2010 07:04am | #10

          Except that the area at the ridge is the ONLY area of the "attic" that is well ventilated, so the odds of condensation in the insulation above are virtually nil.

        2. Clewless1 | Jun 12, 2010 09:38am | #12

          That would be the case if he has a leaking roof or ice daming and such. Doubt that condensation onto the roof substrate would collect and show evidence at the higher parts of a cathedral ceiling. Doubt that it would necessarily even show up inside. For it to drip back would mean a LOT of moisture. Even so, it would have a tendency to run down the sheathing first and show up at lower elevations.

          1. davidmeiland | Jun 12, 2010 11:52am | #13

            I agree with you

            ... assuming that there is no insulation directly in contact with the underside of the roof sheathing. If there were, condensation on the underside of the roof sheathing would wick down to the drywall.

            As far as I'm concerned, the issue here is condensation on the interior face of the drywall, promoted by high interior humidity migrating from the crawl space, aided and abetted by cold air leaking thru the ridge vent. 

            I have a small job to look at this morning, homeowner says there is mold growing on the underside of the roof sheathing in the attic in one area. I have 3 of these and will be planting them in the house and attic for a week, to look at whether changes in RH inside the house and attic are possibly related to changes in RH in the attic. A second floor bathroom that is heavily used by teenagers... with older can lights and possibly a leaky and/or under-utilized vent fan are suspected.

            http://www.ueitest.com/product-thl1.html

          2. Clewless1 | Jun 12, 2010 12:24pm | #14

            Generally, if insulation is in contact w/ the surface, that surface won't have condensation on it. That's the general rule of condesation ... make sure you install the insulation in contact w/ the cavity sides and that helps ensure there is no condensation on the surfaces.

            You have 3 of what?? I think you are right in terms of e.g. recessed cans and teenagers from heck using the shower, etc. Likely sources. Not sure why you want to measure the RH, really. Just fix the problem. It's coming from inside the house. Check the exhaust duct. Is it connected? Does it have a positive connection to the exterior? Is it free of e.g. flex duct that will restrict it's ability to flow effectively (which might result in more humid air going up through the recessed lights)?

            Recessed lights can be notorious for leaking air into the attic and causing all kinds of havoc. If they have these, consider the possibility of boxing them in and sealing them so they won't leak air.

            If he has mold in his attic, he undoubtedly has some kind of a significant leak (from inside). Moisture like that doesn't originate from outside the house usually (I'm assuming you are talking about a temperate climate where there is a winter vs. the humid/hot SE).

    2. Clewless1 | Jun 10, 2010 08:12am | #8

      "I'm thinking it's from

      "I'm thinking it's from condensation at the ridge."

      What is from condensation at the ridge? The mold? Of course the mold is from that. A vapor barrier wouldn't have changed that. The mold is a symptom to a problem. The solution in this case is conceptually not a properly installed vapor retarder. A properly installed vapor retarder wouldn't have changed this condition much ... although technically, there may well be more mold/condensation if it were properly installed.

  5. SWQPjprdkG | Jun 11, 2010 03:20pm | #11

    Thank you all for your input. I will present this info to my client and proceed from there. If time allows and my memory serves me I will post an update at the conclusion.

                                                                        Thanks again,

                                                               Looking Forward,

                                                                         RGB

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