bumbleandpea,the very first thing that needs to be done is a call to your builder to get your hvac company to check the performance of the system.There are a few things that can cause sweating duct.Slow airflow due to a dirty filter,dirty evaporator or low charge.I have seen brand new systems that the builder neglects to change the filters during construction and causes system problems.If the system checks out ok you may need to ventalate your crawl space so that your duct does not reach its due point.If all else fails you can install a dehumidifier under your house,but it must be sealed from outside air.Most of the sweating systems I have seen were fixable with system adjustments or repairs.If they changed the filters too late(which could have caused the sweating) you will need to dry the system out in order for it to not sweat.The insulation must be dried out or it will continue to sweat after the problem is fixed.Also make sure you have a plastic barrier covering the ground underneath to keep moiture from rising.

Most of the time I have found the problem to be that the seams were not sealed on the ductwork, any air leaking out cools the insulation below the dew point and it sweats like a big dog. You can do a little test simply cut a slit in the insulation where you can feel a duct seam and do a feel test, you will probably have a good bit of air rushing out. If the crawlspace is fairly tall (yeah right) and the ductwork is not jammed tightly against the floor joists (another yeah right) they simply need to yank the insulation seal the duct seams properly and reinsulate with NEW minimum 1 1/2in or 2in duct wrap being careful to seal all insulation seams also. At this point it sounds like the insulation is fully soaked, best to start from scratch just have them come back and do it right. Hard to visualize how much water you have but if you are getting big puddles you definitley have some issues to be dealt with. Your crawlspace does need good ventilation high humidity levels in a crawlspace can cause even well sealed duct to sweat and can be very detrimental to wooden floor joists over a long period of time you might have your builder double check the sg footage of crawlspace vents to be sure it meets codes. The new termite treatments they have out with are only good for 10 years (chlordane was banned years ago it lasted 35 years) so you are creating a open invitation for termite problems down the road if you do not fix it.

Leaking duct work will not cause that problem.I have seen 1"ductboard sweat when it reaches its due point.Actually leaking duct can stop the sweating in some cases.A recent abnormal amount of sweating duct systems have poped up in the last few years due to better sealed duct.If it was a small area I might agree but a whole duct system is another problem.

i have the same problem. do you know what is wrong?

Is it also not possible that the moisture is condensation from the air in the crawlspace? It might be a good idea to put a hygrometer (humidity meter) in the crawlspace, and close it up for a few hours and see what it's reading....perhaps even better still, a remote one so you can read what it's seeing without opening the space up...

I agree that for the most part it's important to vent those sorts of areas really well to avoid future damp issues and termite problems - they love moist wood - but you should be able to limit dampness problems in there for the most part.

Insulated or not (and I don't know a lot about that side of it) if there's enough dampness in the air, the ductwork will still be the coolest part of the room and will therefore have moisture condense on it.....

Since it's such a new house, is it possible a) that concrete/blockwork etc is still drying out, or b) there's a leak in the plumbing, say a drywall nail through a pipe that's allowing water to run down to the lowest point, ie, the crawlspace?

I agree, though, this isn't something to ignore or treat lightly, and unless your builder or ac person demonstrably solves the issue, you should consider engaging an independent expert to root out the problem and suggest the proper solution....otherwise, you get builders/contractors just inventing ideas/causes/solutions just to get themselves off the hook and to get out of doing any further work.

Your house should be covered by a warranty, I don't know how long the law states but in Australia, it used to be 7 years...but don't wait that long!

I don't think I was posted since I tried writing prior to registering but my message was that my new wall unit stopped the condensation when I raised the thermostat level on the unit from 72-80 degrees; super heated coils could be contributing to any other troubles you may be experiencing. It's worth a shot, to save any new duct work you may have to put in.

That's awfully cold in the house- 71?. Systems are designed for comfort range 74-75. If you keep it that cold, you may need some venting airflow in the space and/or more duct insulation. The moisture also comes from the air surounding the ducts- seal the insulation airtight and the moist air can't reach the cold metal ducting.

Water vapor is condensing on your cold ductwork. What I would do is look for an insulating contractor in your area that deals with "closed foam" insulation. This foam has a R factor of 7 per inch. Do a search on Google and check it out. I would have the entier crawl space insulated. I would think that the builder should have some responsibility for what is happening. I know that AC systems are engineered to run at certain temps but it is possible to still have condensate even if you have your thermostat set at 76. Depends on dew point. If you're in a developement chances are your neighbors are having the samw problem. If you can't find a contractor to do the work check this site out www.tigerfoam.com. Good Luck!!!