Package Unit - Condensation leaking down return duct

[personalt]

I am the GC of condo conversion project where a package unit was unstalled on the roof to service the top floor condo. The roof return duct has maybe a 4 to 6 foot run before it penetrates the roof. The duct is insulated on the inside and has flashing cement on the outside.

Everything was fine in the summer but during the first below freezing day in Decemeber condensation started to form inside the return duct and then dripped down inside the unit from the return vent. I opened up the unit and took a peak inside the duct, the insulation appears to have been installed properly and is complete. I did notice that the amount of flashing cement on the underside of the duct was really light so we smeared some more on the bottom.

We had no problems for the rest of decemember and early january, but I am in NJ and we had a really mild winter. Today was the first really cold day since and we started to get condensation forming again.

I have a call into my sheet metal guy but was told he was away for a few days. I am assuming the insulation is not sufficient? Is there a good method that we can use to add additional insulation to the outside of these ducts? Is that the right move?

[spotts]

Have someone spray that foam crap on the outside. http://www.bobvila.com/TV_Showrooms/Honeywell/Honeywell_Images/applying_spray_foam_insulation_1000x957.jpg

[personalt]

Thanks for the reply.

I was thinking that but I dont believe that is available in small quanities. I looked into something that for a house interior and they charge a ton of money becuase they use a $75K rig to spray. If that is the case I couldnt see someone who could insulate these 4 feet of duct for a reasonable cost.

Maybe I could use flashing cement to adhere ridigid foam but I was wondering what everyone else does.

[cracker]

Have someone spray that foam crap on the outside. http://www.bobvila.com/TV_Showrooms/Honeywell/Honeywell_Images/applying_spray_foam_insulation_1000x957.jpg

Mr Spott is that urethane foam or is that the water base foam ??

[mechanicalmaster]

You could have the exterior insulated and then wrap that w/ sheetmetal. Have seen that on exposed roof duct before. What thickness is the Duct liner now? Should be at least 2 inch in your area I would think.

[madhat]

You need a Froth Pak 180 by Dow Chemical. Wear some really old clothes, including shoes, rubber gloves, eye protection, and hair protection. Apply on a wind less day, high humidity will give you a better yield. Soon as it warms up coat with a heavy duty latex paint, IE Floor paint.