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retired framer
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sorry, what do you see there? are you referring to the rusted screws?

What's worrying me now is that I have had the AC off for over 3 hours now and it's still dripping. could having the AC on this morning from 9AM-12:30 have caused this much condensation. I mean, it was pretty darn hot today, but usually I have the AC on from 8:30AM onwards until 8PM, and typically after 6-7 it stops dripping.
I suppose another issue is that there's probably still some residual water still trapped in-between the roofs that hasn't gotten a chance to evaporate as I have been using the AC nonstop the last month or so.
See the flap in the black square.
 

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Discussion Starter #82
See the flap in the black square.
That looks like a badly cut piece of insulation to me. right above that should be a hole that leads to a a supply duct in the front of the house. do you see something else there could be problematic?
 

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retired framer
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That looks like a badly cut piece of insulation to me. right above that should be a hole that leads to a a supply duct in the front of the house. do you see something else there could be problematic?
Could just be loose insulation I guess, Are those wood frames inside the ducts. I have not seen that before.
 

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argh. I hate to introduce more variables into this equation, but how likely is it that I would have an airleak in the duct that goes into the ceiling? what is a good way to test that out? I guess if it's an airleak, that would be even worse that the cooler uninsulated surface right?
If the air duct had a leak, I think that could make things worse, as there would be a greater amount of cold air to mix with the warm humid air. It would be like having a bigger duct surface area.

Another thing is my hygrometer is telling me that in the ceiling area right now its 113F and 67% RH. I plugged that into the dew point calc and it says the dew point is 100F. does that mean if something is 100F or cooler touches that air, then there will be condensation that forms on that surface?
can my ambient air in the that room hit the ceiling air, and then that creates condensation on whatever hot surface is up there? sorry for the redundant questions, I'm just trying to understand how the dew point works. thanks.
It means that when the 113F air comes in contact with the cold air duct and starts to cool down, once it reaches 100F condensation will start to form. As this now 100F & 100 RH air cools down even further to say 80F (just making up numbers for example) then more water will condense from the volume of air that was originally at 113F & 67RH. AFAIK the heat transfer rate becomes more nonlinear around the dew point (and freeze point) but bottom line this hot moist air must shed water as it is cooled down to whatever equilibrium point is reached as it comes in contact with the cold air duct.
 

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I don't have the AC on right now :) but I know the house is usually around 77F and 55% humidity when I have it on when it's 95 outside. for example, right now my ceiling is registering 106F and 93.5% RH. it's coming down at 3 different locations now. The fact that I had the AC on earlier I think really screwed me up. now I can't determine if its really from the AC or if it something else. But if it's not the AC ducts, I don't know what else it can be... the contractor here is now saying that the ceiling is "crazy hot" and that water is forming, but scientifically I don't know how that can happen... I was under the assumption that the HOT air in my ceiling has to come in contact with something cool enough to create that condensation. it's not like it can just spontaneously create water from the heat.
Now if the water is coming from somewhere else, then I don't know... but one thing for certain is that the water always drips in the afternoon (when it's hottest).

FYI, the ambient temp upstairs right now is 85F and 49% RH.
You are correct to question the "crazy hot" comment. By itself a rising temperature would lower the relative humidity, preventing any water from forming. But as everyone living on the eastern US knows crazy hot often means very humid. So in that regard the contractor was probably just thinking about this humid air, thinking that water will form somehow, somewhere.
 

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Discussion Starter #87
If the air duct had a leak, I think that could make things worse, as there would be a greater amount of cold air to mix with the warm humid air. It would be like having a bigger duct surface area.


It means that when the 113F air comes in contact with the cold air duct and starts to cool down, once it reaches 100F condensation will start to form. As this now 100F & 100 RH air cools down even further to say 80F (just making up numbers for example) then more water will condense from the volume of air that was originally at 113F & 67RH. AFAIK the heat transfer rate becomes more nonlinear around the dew point (and freeze point) but bottom line this hot moist air must shed water as it is cooled down to whatever equilibrium point is reached as it comes in contact with the cold air duct.
Do you know of any straightforward ways to test if there are any airleaks in the duct?

So for something to condensate, there has to be a "cooler surface", or can you have a hot "110F surface" come into contact with 88F 50% humidity and that would create water?

I'm really hoping to get zero leaking tomorrow from not turning on the AC. Today was disappointing because I thought that I had it off and then realized I had it on for 3 hours. perhaps me having all of the windows open upstairs allowed the outside air to come in and feed the cold duct thus causing a lot of condensation. I noticed that I had a similar amount of water dripping today even though I just ran it for 3 hours vs running it for 12+ hours a day.

If it still leaks tomorrow, and I don't have the AC on, what else do you think it might be? I'm a little fearful that that might happen, and then maybe the contractor will say "told you so" with his wacky crazy hot ceiling statement. and I will really have no clue where its coming from. ha.
 

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Discussion Starter #88 (Edited)
Another question regarding the insulation on the main supply duct. Current there are three sections in play

1. Above roof duct that is internally insulated
2. Below ceiling duct which is externally insulated
3. 2 ft above roof, and inbetween roofs section, which has zero insulation

If I just add internal insulation to the section that has no insulation now, should that fix the condensation problem (assuming that is the issue)? Or do I need to extend the internal insulation as far down the duct as I can, so basically overlapping the external insulation portion of the duct as well?

see attached illustration. thanks.
 

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Discussion Starter #89
another data point is that I have a leak sensor right next to the hygrometer sensor, and today the leak sensor went off early afternoon and it's still showing wet. Whereas the other day, it also went off in the afternoon, but about 30min-60 min later the alarm went away. The difference is today I didn't have the AC on in the afternoon. The other day, I had the AC on all day long. so maybe the AC is actually drying out some of the moisture in the ceiling? but is it doing that, or is it creating MORE moisture with the condensation? ughh...
Another thing is that there seems to be a correlation when the leak sensor kicks off and temp. I looked at the logs, and both times it was very hot in the ceiling area, about 100F+. perhaps that's when condensation is produced the most. but strangely enough, when my leak sensor kicked in today, it was ~1:39PM, and I had already shutoff the AC for an hour...
 

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Discussion Starter #90
I reported the drying time incorrectLu For the other day. It didn’t dry in 30-60 after I first Ed received the wet alert. . It actually didn’t dry until almost 7 hours later. Today it look about 9 hours.
 

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right now my ceiling is registering 106F and 93.5% RH. it's coming down at 3 different locations now.
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According to this calculator, with the temperature and humidity conditions you provided of 106F and 93.5% RH, if the temperature of a surface in that environment is 103°F or below condensation will form.
 

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Do you know of any straightforward ways to test if there are any airleaks in the duct?

So for something to condensate, there has to be a "cooler surface", or can you have a hot "110F surface" come into contact with 88F 50% humidity and that would create water?

I'm really hoping to get zero leaking tomorrow from not turning on the AC. Today was disappointing because I thought that I had it off and then realized I had it on for 3 hours. perhaps me having all of the windows open upstairs allowed the outside air to come in and feed the cold duct thus causing a lot of condensation. I noticed that I had a similar amount of water dripping today even though I just ran it for 3 hours vs running it for 12+ hours a day.

If it still leaks tomorrow, and I don't have the AC on, what else do you think it might be? I'm a little fearful that that might happen, and then maybe the contractor will say "told you so" with his wacky crazy hot ceiling statement. and I will really have no clue where its coming from. ha.
No, not in the context discussed here. The amount of water vapor that air can hold is a function of temperature and pressure. Where higher temperatures and higher pressure can hold more water in the vapor state. Heat the 88F & 50 RH air and its relative humidity will drop without there being an external source of water to evaporate.

Consider the summer outdoor weather cycle, as the daytime air heats up from solar radiation the air takes up more water vapor through evaporation. That humid air is lighter and rises up to a point where air pressure drops and has difficult time holding the water vapor. Causing clouds to form and rain. It is why rain is typically associated with a low pressure system, as the air can't hold as much water as a high pressure system.
 

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Another question regarding the insulation on the main supply duct. Current there are three sections in play

1. Above roof duct that is internally insulated
2. Below ceiling duct which is externally insulated
3. 2 ft above roof, and inbetween roofs section, which has zero insulation

If I just add internal insulation to the section that has no insulation now, should that fix the condensation problem (assuming that is the issue)? Or do I need to extend the internal insulation as far down the duct as I can, so basically overlapping the external insulation portion of the duct as well?

see attached illustration. thanks.
Assuming that is the issue, then insulating that section should be enough. Though if you open it up the duct then extending it further to overlap the inside vs outside insulated sections would be wise. And anything you can do to limit fresh most air getting into this gap between the roof layers. I don't know if that gap is there as part of the roof system (to help keep it cooler) or not. But keeping the supply duct isolated from the humid air is needed.
 

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another data point is that I have a leak sensor right next to the hygrometer sensor, and today the leak sensor went off early afternoon and it's still showing wet. Whereas the other day, it also went off in the afternoon, but about 30min-60 min later the alarm went away. The difference is today I didn't have the AC on in the afternoon. The other day, I had the AC on all day long. so maybe the AC is actually drying out some of the moisture in the ceiling? but is it doing that, or is it creating MORE moisture with the condensation? ughh...
Another thing is that there seems to be a correlation when the leak sensor kicks off and temp. I looked at the logs, and both times it was very hot in the ceiling area, about 100F+. perhaps that's when condensation is produced the most. but strangely enough, when my leak sensor kicked in today, it was ~1:39PM, and I had already shutoff the AC for an hour...
Yes, it is a cycle. The conditioned air inside your house should drop in humidity, as indoor water vapor is shed at your evaporator coil as the air is cooled and the waste water drains down the condensate line. The cooler air coming back inside the home should then be at a lower humidity. But your duct work is adding back new moisture by condensing vapor from the hot outside air (according to the theory that we are currently discussing).
 

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Discussion Starter #95
***********************************************
According to this calculator, with the temperature and humidity conditions you provided of 106F and 93.5% RH, if the temperature of a surface in that environment is 103°F or below condensation will form.
Thanks Sitizen! I will look into this some more. according to my hygrometer, it's 97.5F and 93.7% RH in the ceiling space between the layers of roofs. I wonder if the sensor is accurate. If the sensor is sitting on a little bit of water, I wonder if throws off the reading.

That said, the HVAC system has been off since 1PM yesterday. And right around 1:45PM I noticed a small puddle of water from the dripping. so whatever it is seems to be coming out when it's hotter (currently the temp in the ceiling is 97.5F and 93.7% RH, and 81F 55%RH in the room, and 81F and 56RH outside)
What else could this be coming from? one thing to note is that the plywood layer above the 2nd roof is still pretty damp, so could the heat be making the plywood "sweat" and causing it to drip?

Note that the roof does get incredibly hot, and im sure that heat transfer to all the layers underneath there...
 

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Discussion Starter #97 (Edited)
I just used a moisture meter is the plywood in the dripping area and it’s showing 43% so I’m sure that whole piece is water logged. And needs to be dried out. Question is does the wetness there cause the dripping to happen?

So I know i can't rule out the AC causing the underlying "wetness", but since it is still dripping now without the HVAC on, im not so sure I can rule out the roof from being an issue because what if there is a small leak somewhere that is infiltrating the layers and then soaking the plywood, and then when it gets hot enough, the plywood "sweats" and drips.
I'm not sure if that's based on any science at all... what do you guys think?
 

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Difficult to really know what is occurring there. From the video it looks like that piece of sheathing is saturated. When the roof heats up and expands slightly that may provide a better channel for any trapped water to flow. IIRC I believe you said that this area is downhill of the supply duct, so it is could be condensation collected from the days before.

That area of the roof will need to be replaced at some point. Until you get the ceiling dried out it may be difficult to really pinpoint the source. Even if you can not totally remove those boards directly around the supply duct it might be worthwhile to carefully cut or drill a hole into that layer without penetrating the roof to see if you get a more immediate flow when the AC is on. Of course it is up to you to decide how far to continue probing, I don't know what might become too destructive in trying to seek out the source. Whether it makes sense to first try and add insulation to see if that works. Though it seems that this whole section of roof may need to be replaced sooner or later.
 

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retired framer
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I just used a moisture meter is the plywood in the dripping area and it’s showing 43% so I’m sure that whole piece is water logged. And needs to be dried out. Question is does the wetness there cause the dripping to happen?

So I know i can't rule out the AC causing the underlying "wetness", but since it is still dripping now without the HVAC on, im not so sure I can rule out the roof from being an issue because what if there is a small leak somewhere that is infiltrating the layers and then soaking the plywood, and then when it gets hot enough, the plywood "sweats" and drips.
I'm not sure if that's based on any science at all... what do you guys think?

Did you have the plywood installed over the old roof when you did the new roof?
 

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Discussion Starter #100
Did you have the plywood installed over the old roof when you did the new roof?
No, the plywood was from the previous roofing system. the latest roof I put on was to fix a pitching problem towards the back of the house, and that part needed new plywood, which was done, and then a new rubber roof(membrane) was torched over the repaired part and the rest of the roof.
 
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