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Originally published in Interiors & Sources

09/10/2008

Roof Surveys and Plans

By Richard L. Fricklas

 

Acronyms, such as GPS, TPO, MB, EPDM, IR, UV, VOC, NRCA, ASHRAE, RCI, FM, UL, etc., either enrich or confuse the roofing environment. Just when you thought you had things under control, someone uses “albedo,” “emittance,” “green,” “vegetated,” “cool,” “carbon footprint,” “megapixels,” “flash drives,” or some other term that tends to make you uncomfortable. Tools like cell phones, Bluetooth, Google®, text messages, etc. are ubiquitous, but they only save time if we’re willing to spend time trying to master them in the first place.

Just a few decades ago, thermal imaging of roofs (and of buildings in general) was introduced as a powerful weapon in detecting heat loss or gain in roof systems. Handheld infrared cameras were the beneficiaries of “sniper-scope” technology that could detect the enemy in the dark from the heat emitted from their bodies or vehicles.

Early infrared roof survey devices were heavy and cumbersome, required working at night, and were ineffective if the roof surface was wet. Today’s generation of devices are lighter in weight (if not in cost), but still require a difference in surface temperatures and a good measure of judgment to reliably identify where water is trapped. Thermal anomalies still require site visits and possibly also test cuts during daylight hours to judge if the “hot-spot” was actually due to wet insulation and, if so, to gather some information about how much water is actually trapped. There still isn’t an agreed-upon criteria regarding how wet is wet. No matter how high tech the equipment, under-deck heaters, roof patches, and changes in deck type, insulation type and thickness, or interior use can still mislead an inexperienced thermographer.

Ironically, thermal (and other instrumented) roof surveys are often less effective today because many roofs now use cellular foams (e.g. polyisocyanurate or polystyrene insulations) that usually, unlike their facer sheets, do not readily take on water like wood fiber, perlite, and glass-fiber insulations used to. In addition, many elastomeric roofs may be surfaced with ballast or are even vegetated, effectively hiding all but the most extreme thermal footprints. The light colors of cool roofs have high albedo (reflectivity), so they don’t absorb as much heat during daylight hours as a typical bituminous roof might, so the temperature differential between “wet” and “dry” is reduced.

Professional roof consultants are the ones most likely to take advantage of today’s survey devices, whether they use the principles of infrared, nuclear, and capacitance to indirectly identify potential areas of trapped water. Roof plans are typically generated by the consultant (if not already available) to depict locations of roof drains, direction of water flow, rooftop equipment, skylights, curbs, and flashings. Reports today often include digital photographs of important features, and may include recommendations or conclusions regarding roof condition. The U.S. Corps of Engineers uses its ROOFER program (a remarkably objective, if not time-consuming, method of establishing relative roof condition ratings, fully digitized and computerized).

In some instances, the military has conducted nighttime flyovers using either fixed-wing aircraft or helicopters to conduct the thermal imaging. The Corps has developed a method of preparing roof plans from the information gathered during the flyovers, using scaling techniques based on the known size of features on the roofs, such as HVAC units. Commercial image vendors are using satellite images with success as well.

Today, with satellite imaging, it’s possible to download aerial images with remarkable clarity directly to your desktop using infrared and visible light. Subscribers to Google Earth Pro may download fairly high-resolution photos of a known scale, allowing consultants to make roof-plan drawings of larger roof areas.

At the same time, portable global positioning system (GPS) devices and handheld computers with customized roofing software enable a roof-survey team to quickly measure, locate, and photograph all roof features of interest. This information is automatically organized and compiled so that conditions, observations, conclusions, and recommendations can be quickly communicated with back-up documentation.

Yet, with all of this survey power, there are some things that only the building owner and manager can do. One that is not done often enough is to identify what items on the roof are no longer in service. Every penetration on a roof surface is a potential leak, both of water and of heat energy. Payback on removal can be quite quick, especially for large curbed equipment. During reroofing, not having to work around and flash any unused equipment is a cost savings.


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