Can a Flat Roof Have a Problem With Humidity?

Flat Roofs & Moisture

• Like all roofs, moisture enters a flat roof by way of either rainfall or moisture that is already present in construction materials when the roof is built. A typical flat roof construction on either a commercial or residential structure will consist of a near-impermeable vapor barrier, insulation and an impermeable roofing membrane. This construction often creates a water vapor trap whereby water is trapped between two insulation membranes with no means to escape. This problem is often created or exacerbated by the failure of the builder to allow the moisture an escape path out of the roof.

Problems

• When moisture is trapped between two layers of insulation, it can soak the insulation and diminish its effectiveness, leading to decreased energy efficiency of heating and cooling systems, which in turn leads to higher energy costs. Excessive moisture in the roof can also create ideal growing conditions for molds and mildews that deteriorate wooden parts of the roofing structure. A Canadian public health study conducted a few months prior to time of publication also suggests that moisture and mold in flat roofs are among the leading contributors to childhood respiratory problems.

What to Do

• As noted, the basic problem of flat roofs and excessive moisture is that a typical flat roof design traps moisture between two layers of insulation from which it cannot escape. Unfortunately, effective moisture control methods for flat roofs are all preventative in nature and tend to not be effective at drying a flat roof that is already wet. If you know you have a moisture problem in your flat roof, you will need to pull out the insulation and replace any that has been compromised due to water-logging. Thoroughly dry the wet parts of your flat roof before continuing.

Preventing Future Problems

• To dry a flat roof only makes sense if you take steps to prevent future moisture problems; otherwise, you will be stuck with the exact same repairs a short time later. Breather vents or stacked vent installed strategically in the roof are the most effective means by which moisture can escape a flat roof. Vents should connect from the roofing membrane to the air above the roof and should be covered so that rainfall does not enter the roof through the vent.