mold on ducts

[bennytec]

1940's house 5k sq ft divided into 5 or 6 apartments


The upper level is controled by a lennox in the attic.
The lower is controled by a normal furnace systemn.
When we first got the contract for maintenance and this building the Filters looked 3 years old and the outside of all the ducts was covered with black mold. Inside were mold free. We cleanned the burners and replaced the filters with a 4 inch pleated in stead of the dime store cheap-o's. We cleaned all the mold off with bleach. When insulated with foil back.............. 3 Months later we stopped by to checked the filters and noticed the insulation on the ducts were wet and some had fallen down. and there as water all over the floor under all the main duct trunk. We checked the pressures on the A/c unit everything was fine.
The basement is just storage not climate controled. Can this be changed if we open a supply and a R/A ?
Any Ideas ?

[teddy bear]

Cold ducts in a damp basement require double insulation with a air tight vapor barrier on the outside of the insulation. If the ducts sweat, the concrete floor and walls are also damp and grow mold. No insulation is required on the ducts and mold will not grow when the basement is dry. Better to dehumidify the basement to less than <50%RH with a good dehumidifier. Suggest 1 pint of dehumidication per day per 20 sq.ft. Check EPA "energy star" for capacity and efficiency.
http://www.energystar.gov/ia/product..._prod_list.xls