Jimmy Miller is trying to solve a condensation mystery in a Florida ranch-style home that is being renovated. Even though the air conditioning equipment appears to be operating normally, humidity inside the house is between 60% and 65%, and return ducts located in the attic show significant condensation.

The 1,746-square-foot house has R-19 insulation between the rafters and between R-15 and R-20 of rigid foam above the roof sheathing. Steel roofing completes the assembly, Miller writes in a Q&A post at GreenBuildingAdvisor.

Although the house originally had vents in the wood soffits, the soffits have been covered with vinyl. The metal roof doesn’t appear to have a ridge vent.

“There is quite a bit of condensation on the return ducts in the attic,” Miller writes. “We have had two reputable heating and cooling contractors come to assess the situation to no avail. The owner attempted to contact the original mechanical contractor, but has not been able to speak to anyone yet. The owner is nine months pregnant and afraid the mold will be extremely harmful to a newborn.”

High indoor humidity is now causing delays in the project — the sooner the problem is corrected, the better. That’s the topic for this Q&A Spotlight.

Is the attic conditioned or unconditioned?

To GBA senior editor Martin Holladay, it initially looks as if the attic is unconditioned. That is, humid outdoor air can get into the attic, and the space is not air conditioned in the summer or heated in the winter.

“In Florida,” Holladay says, “that means that your attic is filled with hot, humid air. The humidity in that air will condense on any cold surfaces, including air conditioning ducts. The best solution to this problem is to seal up all of the ventilation openings into…