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I have a similar problem. My house is a beach house, built on 8' pilings. The area under the house is open. Yesterday was hot and humid and we had the A/C on. I noticed some condensation on the exterior surface of the brownboard under the house today that corresponds to where the HVAC duct work is located. WHat would cause this and what is the solution? I questioned the insulation of the ducts when the builder was enclosing the ducts (I didnt think there was sufficient insulation around the ducts) but the builder blew me off. Is this what is causing the problem?
 

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The joists should be insulated and covered. The duct-work may be leaking, check for foil taped or black tape on every joint, even the individual elbow joints, and insulated. Pictures would help.

Gary
 

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The joints were taped and covered but when they were wrapped with insulation they did not form a complete wrap as far as I could tell. I suspect the shoddy unsulating is what is causing the problem now.
 

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Hey Gzgirl,

The condensation on the brownboard is accumulating because warm, moist air is contacting a cold surface. This causes the water vapor in the air to condense or turn into water. Just like the beads of water that form on a cold glass of lemonade on a summer day.

You're contractor straight out lied to you about the insulation and now you can visually see what's happening. You're losing tons of energy because the air inside the ductwork is losing its cool as it moves from your A/C unit to the rooms in your home. This cold energy is transferred to the brownboard.

In the winter, this reverses and the hot air from your furnace turns into luke warm air as it loses some of its heat to the brownboard and outside air.

The solution to this problem is not beyond a DIY fix, but it is a major undertaking. You would need to:

Remove all of the brownboard.

Inspect the ductwork and seams for gaps and leaks.

Seal the ductwork with mastic or HVAC foil tape

Air seal and insulate not only the ductwork but everything on the underside of
the floor. (probably with spray foam)

Then put it all back together.


I know it sounds like a lot of work. But at least you'll be at the beach:thumbup:
 

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Thanks so much. The home is still under warranty and this is one I am going to fight on, for what it is worth. But I am prepared to tackle it myself if I do not get any satisfaction from him.

On another note, the brownboard will eventually break down with the elements and someone suggested pool paint over the brown board to protect it. It seemed like a good idea except that I wondered if the latex nature of the pool paint would act as a second vapor barrier and, if so, would that create an additional problem over time or would it be beneficial?
 

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"In the winter, this reverses and the hot air from your furnace turns into luke warm air as it loses some of its heat to the brownboard and outside air."------ I would think the furnace supply air would stay hot but lose some volume due to the leaks and the duct air is of higher pressure than outside air not letting in air when operating.......

I wouldn't use that for an argument point, though I've been wrong before.LOL

Gary
 
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