This was determined by using an IR survey to detect moisture content. The test cuts also revealed delamination between plies, as well as between plies and the cover board. Only isolated moisture was detected during plastic sheet tests.
The venting system was mechanically attached to the structural deck through installed base and cap sheet. New plies were mopped and a cap sheet with limited vents was installed. The solution preserved the existing assembly while allowing the blisters to be repaired and trapped moisture to release over time. The owner was also able to avoid replacement costs, as well as the associated demolition waste.
Insulate for Energy Savings
While maintenance preserves the existing condition of your roof, you may need to take additional measures to improve its thermal performance if it’s subpar to begin with.
According to Kirby, the ideal installation includes a double layer of insulation with adhesive or fastener attachment of the bottom-most layer. If your roof wasn’t designed with this in mind, there are a variety of retrofit opportunities to increase your roof’s R-value.
“Insulation is the main driver of efficiency in roofs and ultimately trumps roof color,” Kirby says. “Once you have the right amount of insulation, roof color doesn’t have much impact on internal energy use.”
He uses the analogy of winter coat colors. A thin black jacket may absorb a little solar heat but still lacks adequate insulation to keep you warm. Conversely, a well-insulated white coat won’t absorb much sunlight but will nonetheless keep the cold at bay. If both jackets are properly insulated, however, the color will have little bearing on comfort.
When evaluating the thermal performance of your roof, look for areas that enable heat transfer through convection or conduction. Metal fasteners and gaps larger than a quarter inch in board joints are common culprits that reduce insulation value. To minimize thermal bridging, use non-metal fastener plates.
“You can also install a cover board over fasteners. It doesn’t provide much insulation, but it will separate the metal fastener from the underside of the membrane,” Kirby explains. “Spray foam insulation is another option that eliminates fasteners altogether.”
Air infiltration can also wreak havoc on your energy consumption because it’s laden with moisture that carries heat energy.
“Air leakage is as important to thermal resistance as insulation,” notes Kirby. “Air infiltration and exfiltration make up 25 to 40% of total heat loss in a building in a cold climate and 10 to 15% of total heat gain in a hot climate.”
Adding air barriers along penetrations and transition locations can help both thermal and moisture issues. It’s also important to adjust your ventilation system after sealing measures to avoid sick building syndrome or any other ventilation issues. You can even use a blower door test to determine if the building meets code requirements for tightness.
“The insulation layer should be designed as a system and account for skylights, drain sumps, roof hatches, and HVAC units,” Kirby stresses. “The mechanical system in the building should be sized appropriately based on the roof’s actual R-value. This is critical because mechanical systems are designed based on the expected thermal resistance of the envelope. If it’s less than anticipated, then equipment could be undersized and subsequently stressed.”
Keep in mind that commercial buildings consume approximately 20% of all energy in the U.S. As heating and cooling remain the top drivers of energy efficiency, the roof can make or break your thermal performance.
“There are roughly 2.5 billion square feet of roof replacements each year,” says Kirby. “By increasing the energy efficiency of roofs to current code-mandated levels, we could potentially save over 700 trillion BTUs in energy.”
Jennie Morton is senior editor of BUILDINGS.