Ohh.....FFFFFFFFudge!

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  • cwsmith
    Veteran Member
    • Dec 2005
    • 2737
    • NY Southern Tier, USA.
    • BT3100-1

    #16
    Originally posted by dbhost
    I couldn't disagree more. Yes cold does tend to attract moisture, which means the cold AC coils are going to suck the moisture out of the air before it has a chance to even come in contact with a wooden floor.
    Yes, but the problem mentioned is not from moisture within the house, which as you state, "the cold A/C coils are going to suck the moisture out of the air". The problem as stated in the opening post is underneath the linoleum or vinyl flooring, which is "bubbling up".

    First off, cold air doesn't attract moisture... it is the warm moist air that that condenses because of the stark temperature differential as it contacts the colder surface or barrier which separates the inside and outside temperature difference. The purpose of insulation is to dampen that temperature difference and minimize temperature transfer. The idea of a moisture barrier is just that, to prevent humidity from condensing or transferring beyond the barrier.

    When I wrote, "When a house is air-conditioned that moisture will condense on colder surfaces.", I definitely overstated the conditions. I really don't think that the interior of the house would be so cold as to actually cause condensation to form in any visible manner. If so, you'd see the windows fog up on the outside. But, unlike windows, the floor covering is probably the coldest spot in an air conditioned room, and it is possible that moisture could collect underneath, since the floor covering is acting as the first moisture barrier between the warm outside humid air and the dry cooled air inside.

    However, even it there were no air conditioning or temperature differential between inside and out, moisture will condense on the first non-porous, moisture resistant surface it encounters. Examples of that is morning dew, condensate on your tent in the early morning, and underneath anything layed close to ground, even in good weather. Lay a piece of plywood or a tarp on the ground and chances are in a very short time moisture will collect on the bottom. For example, I have and old garage, with an unsealed concrete floor. I don't drive my 95' Miata in any kind of wet weather and certainly not in the winter... so in 20 years, that car has only seen rain a few times and never snow. But I noticed the first year I put it in this garage, the underside was a wet mess that winter. It's an unheated garage so there's no temperature differential at all. But moisture penetrating the garage floor was collecting on the first non-porous barrier it came to... my Miata. Easy cure, I now park the car on a double layer of moisture-proof tarp and the car stays dry.

    Years ago when we were looking for a house, I encountered a very nice looking home, that was destroyed on the inside. Apparently the house had just been shut up. No windows left open. Moisture penetrating the basement concrete was horrible. When the realtor opened the front door, we were practically knocked down my the humidity and stench of mold. It had been a beautiful home, but the floors were all cupped and there was mold on the inside of many of the windows. We went down into the basement thinking that perhaps a pipe had burst. But the plumbing was fine. The basement had a pretty good concrete floor, but the walls were cinderblocks. No cracks, but they too were almost green with mold and there was condensate dripping off the ceiling joists and collected up on the subfloor.

    I have no idea how long that house had been sealed up. Even normal comings and goings would have prevented such damage I think. Venting is very important.

    CWS
    Think it Through Before You Do!

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    • leehljp
      Just me
      • Dec 2002
      • 8429
      • Tunica, MS
      • BT3000/3100

      #17
      CWS: When I wrote, "
      When a house is air-conditioned that moisture will condense on colder surfaces.", I definitely overstated the conditions. I really don't think that the interior of the house would be so cold as to actually cause condensation to form in any visible manner. If so, you'd see the windows fog up on the outside. But, unlike windows, the floor covering is probably the coldest spot in an air conditioned room, and it is possible that moisture could collect underneath, since the floor covering is acting as the first moisture barrier between the warm outside humid air and the dry cooled air inside.
      Precisely.

      I have no clue as to the condensation formulation, but when it hits 90° to 100° for several weeks in a row and a large part of that is 90% or greater humidity, along with a few heavy rain showers followed by 95° heat for several days, it is humid under the house too - without a moisture barrier. And then to keep the inside temp at 73° to 74° during the day, would not this draw condensation to the underside?

      JSUPreston's statements and mine are not isolated incidents in the south, according to my termite inspector who works for a cousin of mine.

      As to seeing condensation, It is common here to see condensation on side windows of the car in the summer when we are having 100% humidity and it is hot and we have the side vent A/C blowing on the windows. NO, I am not talking about the winter fogging, but hot summer fogging.
      Hank Lee

      Experience is what you get when you don't get what you wanted!

      Comment

      • JimD
        Veteran Member
        • Feb 2003
        • 4187
        • Lexington, SC.

        #18
        I am not going to show my wife this. I think her choice of 74 degree temperature to be excessively cool even at night. She turns the ceiling fan on too. I am fine at 76-78. She MUST have a blanket. In the summer. Knowing others keep their houses at 68-70 would probably cause her to turn it down further.

        The science of this has been mentioned but I will still try to summarize in my words. If the dew point of the air in the crawl space is above the temperature of the flooring and/or plywood, there will be condensation. Plywood is a pretty decent moisture barrier but only if it is sealed at the edges. But this problem sounds like the condensation was occurring on and under the plywood. For a long time. Gradually it delaminated allowing the moisture to go higher. Plastic in the crawl space should help lower the dew point. I have that. I do not have insulation. I plan to add spray in, closed cell if possible. I have no signs of moisture in the floor but we have hardwood flooring. That may breath a little. But this is another reason I need to add some insulation. Closed cell would reduce and possibly eliminate crawl space air going to the cooler surface and the underside of the insulation would stay warmer, more consistent with the dew point. Even if condensation formed on the insulation it would be a lot better than it occurring in the wood.

        But again, condensation forms when the dew point is higher than the surface temperature. If you cool to 70 degrees and the dew point is significantly higher than that under the house, the minimal insulation of the plywood will not permit the surface temperature to stay above the dew point and condensation will form.

        Comment

        • JSUPreston
          Veteran Member
          • Dec 2005
          • 1189
          • Montgomery, AL.
          • Delta 36-979 w/Biesemyere fence kit making it a 36-982. Previous saw was BT3100-1.

          #19
          Sorry I wasn't able to respond on Friday. Lee is mostly right. This section of the house (addition in the '60s) does have a crawlspace that gets pretty darn tight. It has several vents that are left open and are not blocked. The ground cover to some of the vents is about 3 feet away. I believe there should be adequate air flow. The inspector said that no pipes were leaking, and the crawl space was bone dry.

          I did remember something Friday night that may play into this. About a year ago, we had to have the shower redone in the master bedroom, which is the next room over in this addition. Apparently when the bathroom was redone back in 2002, they didn't replace the shower pan. It was apparently in bad shape when the shower was redone, but rather than doing the job right, the original contractor just skipped that step. Long story short, the guys that redid the shower last year said that the pan had rusted through. They wound up replacing a bunch of subfloor in the bathroom. Some of that subfloor is 6-8' from one of the bubbled up areas. I'd be willing to bet at this point that the leaky pan did more damage than the AC.

          We haven't made plans on starting this project yet, but I guarantee that vapor barrier will be going down as part of the project. Because of how tight the crawlspace is, we're either going to have to find someone small to put up insulation, or have it sprayed. We will consult with professionals about the best way to do that.
          "It's a dog eat dog world out there, and I'm wearing Milk-Bone underwear."- Norm (from Cheers)

          Eat beef-because the west wasn't won on salad.

          Comment

          • dbhost
            Slow and steady
            • Apr 2008
            • 9209
            • League City, Texas
            • Ryobi BT3100

            #20
            Originally posted by Kristofor
            This would be true if they were running the A/C to cool and dry the air underneath the house. The damp air down there never gets near the cold A/C coils but it does come in contact with the (relatively) cool floor. This is assuming the water is coming from condensation under the house, if it is a pipe leak under the floor or in a wall then all bets are off of course.
            Underneath the house?

            Sorry, my bad. I keep forgetting that not everyone is slab on grade construction.

            I guess this would mean there is a basement? I do remember my parents had a house with a basement, Dad had to keep a dehumidifier running out there from spring through fall to keep the house dry...
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            Comment

            • capncarl
              Veteran Member
              • Jan 2007
              • 3564
              • Leesburg Georgia USA
              • SawStop CTS

              #21
              I hate to say I told you so, my forecast was closer than blaming the AC. If the AC was the problem then half the houses in the South with crawl spaces would have to rotten floors. We had such bad luck with flood induced moisture problems in my previous house with a crawl space that my new house is on a raised slab. No more rotten floors for me.
              capncarl

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