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.

How to Recognize and Prevent Ice Damming

The cold winter season is the time when many homeowners see icicles hanging from their eaves or water coming in the house due to ice damming on the roof. An ice dam is a ridge of ice that forms at the edge of a roof and prevents melting snow/water from draining properly off the roof. The water that then backs up behind the dam can leak into your home and cause damage to walls, ceilings, insulation, and other areas. 

There are three main causes of ice damming:

• Poor insulation from a house ceiling. An attic with inadequate or deteriorated insulation can cause ice damming.

• Lack of ventilation. A house with proper ventilation allows the necessary cold air to mix and cool the hot air from the house, which slows the snow melting down.

• Leaking gaps between the living space and the attic. These spaces allow extra heat to “escape” into the attic, which warms the space and melts even more snow.

Here is what you can do to prevent ice damming:

• Seal the living space.

• Install adequate attic insulation.

• Make sure that the attic is properly ventilated.

Shingle roofs are designed to shed water; they are engineered and installed to reject freestanding water. That is why a good quality leak barrier is needed at the eaves. The most important thing a contractor can do to help homeowners with ice dam problems is to first clean the snow off the roof (following strict safety rules) and then create exits for the trapped water.

Preventing ice dams and icicles may not be possible at all times, but these are measures that can be taken to help stop water from entering the house.