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Identify and fix wet spots on roof




November 7, 2012 - Roofing

Today's tip is to deal with wet areas on the roof effectively. First, check the roof one of three types of moisture surveys: infrared, nuclear or capacitance.

Infrared surveys measure the heat retained or lost in insulation that has become damp. Ballasted roofs aren't a good candidate for infrared surveys because the rock itself retains a lot of heat, giving potentially false readings. Nuclear moisture surveys measure hydrogen atoms in the roof, meaning that any membrane with a large hydrogen chemical component will send positive readings. Water is a good conductor of electricity, and capacitance surveys measure electricity traveling through the roofing material. This won’t work on a roof with wet or ponded areas, and may require modified instruments on EPDM roofs.

If you have 100,000 square feet of roof and four 8-by-10-foot areas are wet, replacing those sections makes sense. But if 30 percent of your roof is wet and it’s scattered throughout the roof, the labor to replace all of those sections probably equals the cost of just tearing off the entire roof.

But what if the roof is leaking just after a recent replacement? It's not that farfetched — due to poor design or installation, many roofs experience water leakage soon after construction.

In many instances, water leakage through a roof membrane can go unnoticed because a vapor retarder at the bottom of the roof system captures the water. The captured water absorbs into the insulation, significantly decreasing the thermal value of the insulation and causing premature deterioration of the roof system.

Generally, the membrane does not allow bulk water leakage. Most leaks through a system arise from unreliable detailing.

Roofing system manufacturers provide standard details for perimeter conditions, which typically have the flashing exposed and terminated on the wall surface. They rely on sealants to prevent water infiltration. Manufacturer details typically do not address leaks around the roof system.

For example, in most instances, roof terminations consist of surface-mounted conditions (exposed termination bars or metal flashing) or reglet-set flashing (a small cut in a wall system to insert the metal flashing). In a brick masonry wall, water can bypass the flashing, infiltrate the masonry, and migrate into the insulation. Instead, the design of roof flashing for a masonry wall should incorporate a through-wall flashing that extends through the masonry to capture and divert water out of the wall above the flashing.

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