Moisture Control in Low-Slope and Flat Roofing Systems

Condensation within a flat roofing system mainly occurs during cold weather seasons when moisture and vapor in the air caused by heat from within the building rising out into the cold roof void above the ceiling. When the temperature of the moisture falls to or below its dew point, the water vapor condenses on the cold surfaces around it causing damage and leaks. Condensation is a particular problem in flat or low-sloped roofing systems above rooms that generate a lot of heat such as kitchens and bathrooms. A flat roof should be designed to minimize condensation and a proper analysis of the positioning of insulation materials, vapor control layers, ventilation, and thermal insulation should be reviewed prior to installation. Here are our tips on preventing the likelihood of leaks on low-slope/flat roofing systems:

During Design/Specification:

1. Provide a positive roof slope. This will provide roof drainage and better ventilation to the outdoors.

2. Provide as much ventilation for moisture "traps" as possible. This can be achieved by cutting back ends of reflective foil/batt insulation which are installed below the roof sheathing.

3. Use insulation above the wood deck. Where low design temperatures or high interior humidity are expected, this method can help keep wood temperatures above dew point.

During Construction:

1. Install roofing over the wood deck ASAP. This will protect the insulation from exposure to the elements.

2. Provide proper ventilation to remove moisture. Moisture build up during the construction of a roofing system is expected due to the curing of concrete and gypsum jointing materials. Proper ventilation will prevent these aspects of installation from having long-term effects on the roof.

During Service Life/Homeowner Tips:

1. Don't let moisture stand a chance. If you own a home with a low-slope or flat roofing system, it's going to require a little more care than a standard shingle roof. Your best bet at maintaining the integrity of your roof and preventing leaks is calling a pro for any snow/heavy rainfall removal - this way you know the job is being done correctly. If you've had any extreme weather (snow. rain, or wind) be sure to notify your professional, this way, they can ensure all roof membrane and HVAC systems are in working condition.