Equipment and Occupant Concerns
Although metal roofs may present the same issues as above, there are different condensation concerns with metal construction.
"Problems are usually related to high relative humidity inside the building and the lack of proper ventilation, insulation, or vapor retarder," says Rodger Russ, North American sales manager of roofing at Butler Manufacturing. "Metal roofs on pre-engineered buildings don't have a solid deck, so their problems are more envelope related. Any time humidity creeps upward of 50%, should moisture-laden air permeate the vapor retarder and insulation and come into contact with the metal roof, there is the propensity for condensation to form."
Manufacturing facilities and large structures like gymnasiums are particularly vulnerable to this kind of problem.
"Buildings that house machines or an excessive amount of people can have trouble," Russ says. "Anything that dumps a lot of moisture into the air is a red flag."
Also keep an eye out for mold and droplets developing on the surfaces of the roof assembly.
One of the easiest ways to mitigate humidity is with basic ventilation, explains Russ.
"For many cases, adding fans can take care of this issue," he adds. "Other solutions include adding more insulation or a more substantial vapor retarder, which is often difficult to do after the fact."
Do Your Due Diligence
If condensation problems conflate, then water leads to mold, wet insulation, and roof failure. Keep a roof system historical file to stay on top of the situation.
Your file should contain a detailed history of the roof installation, repairs and changes, and a maintenance plan, notes James R. Kirby, vice president of sustainability at the Center for Environmental Innovation in Roofing.
It should also contain original plans and specifications, warranties, thorough documentation of maintenance and repairs, and even samples of roof system materials, he adds. The historical file should be kept with the building when sold and purchased, which can be especially useful when tracking the building's use.
In the specific case of a large metal building with minimal insulation and no vapor retarder, the end use of the building was never made known to the manufacturer and engineer, says Russ. It housed a kiln to dry wood, and the excess moisture from the drying process caused insidious problems that necessitated a severe solution.
"No one knew there was a problem until a maintenance worker put his foot through the roof," he explains. "That situation required full-scale replacement."
Chris Curtland email@example.com is assistant editor of BUILDINGS.