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Part 2: Building Envelope Commisssioning Ensures Exteriors Perform as Planned
By David Reid and John Wilkins
June 2012 -
The commissioning effort starts with the assumption that water will penetrate the veneer and to see what happens when it does. Will the water be channeled and drain away from the wall cavity, as it was designed and constructed to do, or will it seep back inside the building? Without building envelope commissioning, no one will know if that wall is performing as designed unless or until there is a problem discovered later, often much later. By that time, the damage from the breach may be quite costly or even impossible to correct.
Testing is more important than ever as buildings are designed to be high performance. Buildings that allow water to leak inside don't do so by design; they do so from imprecision in the detailing of the envelope. Manufacturing and construction industries that have tightened up their detailing on a building's envelope to keep buildings from breathing to improve energy performance, consequently also keep any penetrated water from adequately drying out. Therefore, the escape routes for air, as well as moisture, must be intentionally designed into the wall system.
Manufacturers that have developed systems designed to be watertight find those systems may not be as watertight as intended because there's a lot of imprecision in the field, and contractors often rely on caulk to fill gaps in the exterior of the building envelope. Yet over time, that caulk dries, cracks and separates. As a result, without continuous inspection and maintenance of every square inch of the building envelope over its lifetime, water or water vapor will eventually penetrate the veneer.
While most of the conversation surrounding building envelope commissioning is devoted to building façades, roofing is equally, if not more, critical in contributing to the building's energy efficiency. As with envelope commissioning, roof commissioning should be incorporated through all phases of the process, from early design through post-occupancy. Roof commissioning for conventional and green roofs follow a lot of the same principles, with the exception that green roofs have more components to monitor. The following highlights are essential for an initial understanding of the process:
"Weak Links" in the integrity of roofing systems are the cause of most roofing failures — roof terminations, penetrations, flashing at corners, intersections, eaves, curbs and parapets, and drainage systems. While performing inspections and testing, these conditions must be closely scrutinized.
The Waterproofing Membrane is the most critical component a roof. For green roofs, the membrane needs to be installed by professionals experienced in green roof applications. And these membranes must be guaranteed when submerged in water. Prior to installation, it is imperative that the deck surface is properly prepared — a critical inspection step. After membrane installation and prior to installation of all additional roof system layers, a membrane leak detection test should be conducted using one of several test types. Flood tests typically retain 2 inches of water for 24 to 48 hours. Flowing tests flow water continuously over the surface of the waterproofing membrane for a minimum of 24 hours without closing the drains or erecting dams. Electric field vector mapping pinpoints breaches in the roof membrane by tracing the flow of an electric current across the membrane surface.
Protection Board and general protection of the membrane after installation and waterproofing testing is crucial. Creating a plan to protect the membrane until all components are installed. It should not be assumed that all roofing contractors understand optimal installation protocols — education of all crew members who might be on site during the implementation stages is recommended.
Vegetation-Free Zones on green roofs are 12-inch vegetation-free zones around the perimeter of a green roof, drainage zones, flashing areas and other penetration areas. These help prevent roots from reaching and damaging the membrane and flashings. Wind turbulence at roof edges can displace growing medium and is another reason for vegetation-free zones. Inspections of green roofs are recommended three to four times per year and after major weather events to ensure drains remain free of vegetation and foreign objects.
The use of envelope commissioning in the design and construction process is an effective risk-management tool for owners, architects, contractors and component manufacturers to optimize building performance and reduce energy use, while minimizing liability concerns and remediation costs.
— David Reid, John Wilkins
Part 1: Water and Air Infiltration Can Quickly Compromise Building Exterior
Part 3: Performance Testing Helps Ensure Air-Tight, Water-Tight Construction
Part 4: Finding Energy Waste Requires Knowledge of How Energy Transfers Through Building Components