Imagine we are standing on the roof of a recently-built aquatic centre, where the owner says the HVAC system cannot maintain the proper indoor environment.
Anyone holding an infrared camera can see that something is wrong. Pointing it at the roof parapet, it lights up like a neon sign, indicating either major air leakage or missing insulation. Standing near it, you can hear kids splashing in the pool below and smell chlorine. Obviously, there is something wrong.
Now we open up the cap and look inside. This is what you would see: moisture, mold, rust. This building is only a few years old. So what’s going on?
It's likely the parapet was very poorly air sealed using a flexible, vapour-permeable membrane, and foil tapes were used to bridge gaps. The tapes are not designed to work with the fabric membrane and their adhesives failed under the regularly scorching summer conditions on the roof.
The membrane is not designed to take wind loads, so it tore in some places. It is also vapor-permeable, which allows corrosive water vapor to pass through. Hot, ultra-humid air pours into the parapet, leaving buckets of condensation underneath. In only a few years of building operation, structural steel members already show signs of rust. Without fixing the air leakage, this building will rot from the inside out.
This building had a specification for air tightness, and it was tested several times with blower doors, repeatedly failing to meet its target. Only when they went looking for the cause of the air leakage did they uncover these massive problems. This is an example of when a single commissioning step such as an air leakage test can reveal major issues. An aquatic centre is a high-risk project. Its building envelope must handle exaggerated humidity and temperatures, and if not executed correctly, the result can be serious energy bills, serious condensation, and mold that makes people sick.
Full building envelope commissioning (BECx) would have highlighted potential risks with this building before it was even built. That is because it is a start-to-finish process that entails thorough quality control of the design, specification, construction, inspection, and testing of the entire envelope. In essence, it is risk management. Here are some other building sectors that can benefit from commissioning for air tightness:
Many construction standards for military buildings, including the US Army Corps of Engineers guidelines and the Australian Department of Defence Building Energy Performance Manual (BEPM), require buildings to be tested for airtightness. The military is a classic owner-operator, and when it builds a facility, it is planning for the long term. It makes sense to minimize energy use, obviously for the financial benefits but also to reduce exposure to short- and long-term spikes in energy costs. Energy security aids national security.
But there’s a more sinister reason to seal a building up. The US Centers for Disease Control and Prevention’s publication Filtration and Air-Cleaning Systems to Protect Building Environments from Airborne Chemical, Biological, or Radiological Attacks cites a tight building envelope as a critical component of a system that can effectively manage an airborne attack. What good are the best HEPA filtration systems if outside air can simply leak into the building? According to the guide:
“The envelope of your building matters. Filtration and air cleaning affect only the air that passes through the filtration and air-cleaning device….Outside building walls in residential, commercial, and institutional buildings are quite leaky…Therefore, you cannot expect filtration alone to protect your building from an outdoor CBR release.”
The guide offers the following advice on building envelopes:
“To maximize building protection, reduce the infiltration of unfiltered outdoor air by increasing the air tightness of the building envelope (eliminating cracks and pores) and introducing enough filtered air to place the building under positive pressure with respect to the outdoors. It is much easier and more cost efficient to maintain positive pressure in a building if the envelope is tight, so use these measures in combination.”
Hospitals also need to be constructed with tight envelopes both inside and outside. Construction guides published by the Victorian government recommend testing isolation rooms for air tightness. Such rooms are used to keep the very ill and vulnerable from spreading or receiving life-threatening infections. As a result, doctors don’t want unfiltered air passing into and out of these rooms. Another reason is that tighter room envelopes afford the HVAC engineer greater confidence in their design, and the building operator more control of room pressures, temperatures, and humidity. This makes for more comfortable and healthy patients.
I recently had the opportunity to test a PCL3 (Physical Containment Level 3) laboratory for air tightness. These laboratories may handle dangerous pathogens, and safety protocols required that anything that I brought into the lab had to be disinfected by fumigation or destroyed by autoclave before leaving. These rooms are incredibly airtight. According to the Office of the Gene Technology Regulator, each should be tested every three years for air tightness and demonstrate that they leak less than a total of 20 litres/second at 200 Pascals. If you know about air tightness, you know these numbers are mind-blowingly small. Since I couldn’t bring a camera in to the facility, here is my recall of what the rooms looked like:
The rooms need to be this airtight obviously to keep nasties from escaping, but one might wonder if a person could suffocate in this room? The answer is probably yes, which is why there is plenty of ventilation and highly-tuned pressure control. The laboratory as a whole contains many rooms, and each is maintained at a specific pressure relative to each other, to maintain control over airflow patterns should primary levels of containment fail. If all else fails, each room is outfitted with fumigation ports to pump chlorine dioxide gas into the laboratory and annihilate everything inside. None of this would be possible without leak-proof rooms.
Commercial and Residential Projects
I'm not looking to scare readers by showing extreme examples. In fact, I aim to lead them to think how principles of building envelope commissioning can be applied to everyday projects. For example, consider that every HVAC designer must build oversize equipment because they can’t be sure how well the building is actually going to be built. With better quality control and firm targets to meet, they can have more confidence that their design will meet the load.
We need to drive home the notion that building and testing for air tightness is one of the most basic forms of quality control, and that should resonate with many Australians. The expertise for building better building envelopes exists in Australia. Responsible commercial projects will undertake steps like testing façade assemblies to AS 4284 or AS 2247 to ensure that they don’t leak water or air. Put this in the context of risk management, and a whole-building commissioning approach seems like a great idea.
For every Australian calling for air tightness, there are 10 more asking for more fresh air. This reaction is partly claustrophobia and partly fear of the boogeyman - condensation. But an educated building community knows that air, water, and energy management are intimately linked. For example, the US Environmental Protection Agency’s Indoor airPLUS program requires that homes be built to ENERGY STAR standards, and that they undertake a thorough design-checking and inspection process for water management.
These are not new concepts or concerns. The adage “a building has to breathe” sounds silly to someone with a basic education in building science. Still, I suspect that saying once had a basis in fact: the building envelope must breathe to keep the building (and itself) dry to minimize the risk of moisture damage. Now we know how to minimize risk using modern materials and methods. It’s called building envelope commissioning.