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4/14/2009 12:00:00 AM
Compiled by FacilitiesNet Staff
Roof leaks are a major headache to fix. The good news is that some leaks are predictable - especially as the roof ages. By identifying areas that are prone to developing problems, steps can be taken that will prevent roof problems cost effectively.
Look For Roof Leaks Near Penetrations
Flashings and sealants at penetrations through the roof membrane are common trouble spots. Typically in single-ply roofing systems, penetration flashings are the same material as the roof membrane and are bonded to the field membrane. Inspect the laps, seams and sealants at these locations regularly.
Factory-assembled boots can address field installation issues at penetrations. It is important that technicians properly seal the boot to the field membrane, where problems typically occur.
Roof drains that penetrate a roof membrane can be especially troublesome because rain that falls onto the roof eventually flows over the drain's seal. Drains should be large enough to handle heavy rainfalls, and they should have a screen that stops debris from flowing down the pipe.
Workers should clean the drain regularly to prevent blockage of the screen and install recessed drain sumps. A positive slope in the roof also can prevent ponding around drains.
The best way to avoid leaks at roof penetrations is to avoid penetrations altogether. For instance, ducts, conduits and other piping that runs horizontally across the roof often are placed on solid supports that are anchored to and penetrate the roof membrane at regular intervals. To avoid these penetrations, managers can specify products with adjustable heights and soft feet that rest on the membrane. If a horizontal element must be anchored to the roof, build a curb and secure the element supports to the curb.
Roof Leaks On The Perimeter
Leaks occur near roof edges because of the transition from flexible membrane flashings to inflexible sheet-metal flashings. Technicians should ensure that sheet-metal laps shed water, and they should inspect the sealants at these locations regularly.
Pre-manufactured sheet-metal roof accessories can solve many roof-perimeter problems. Managers can specify custom-made accessories for copings at parapet walls and reglets at masonry or interior rising walls. These components typically snap together, and technicians can dismantle and re-install them during roof-membrane replacements.
Water problems also occur near expansion joints at roof perimeters. To address areas where building expansions and contractions are likely to occur, managers might want to to consider specifying pre-manufactured roof accessories. But managers need to make sure accessories they specify are compatible with the roof membrane.
Condensation And Roof Leaks
Sometimes, a roof might appear to leak in January when the temperature dips below freezing, but the roof might not be leaking. What happens is condensation is created when the warm, moist interior air inside the building contacts cold surfaces or when cold air leaks through the building's exterior skin.
This problem might result from a missing or inadequate air barrier or vapor retarder on ceilings or walls, or from inadequate insulation or ventilation. Cold areas above the insulation in joist cavities or attic spaces must be vented. If natural ventilation is difficult or too expensive, technicians can install a fan that moves moist air out of the cold space.
The Roofing-Mold Connection
Building Envelope: Keep Water Out of the Roof
Moisture Surveys and Roofing Warranties