Air Infiltration Article
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The Affects of Air Infiltration in Commercial Buildings
By Tom Kearns, Detailing Manager, The Facade Group, LLC _______________________________________________________________________ Is air infiltration just a statistic, kind of like how much rain falls in your home town in May? Or is it something that affects most of the things that make a building livable, desirable, economical, a place where people want to spend time. It is important to remember that buildings breathe similar to living organisms and just like living organisms the air movement needs to be managed. Unmanaged air entering a building is kind of like a burglar steeling the comfort of the building and the efficiency of its mechanical systems. Conduct a search on the internet for “air infiltration” and there will be a whole bunch of links to studies, literature and products that describe how to measure it, where it is most likely to come in and how to prevent it. The literature says that in a residence 30 percent or more of the heating and cooling costs are attributable to air infiltration and that moisture, mold, noise, dust, pollutants, insects and rodents pass through the envelope of the house through the same holes that admit air. The air infiltration situation in commercial buildings is similar to residential structures even though the construction may be different. This article discusses what air infiltration is, why it is significant, where it most often comes from, what problems and costs result from it and what can be done about it. In these times of rising utility costs, with the utilities’ capacity stretched and increased concern about our resources of fossil fuels, inefficiency is not something we can afford. First let’s deal with some things that anecdotally would seem to help with this problem. Curtains or blinds on the inside of windows may block the heat or cold that radiates from the glass but they do nothing to prevent or control air that may be leaking in. Some insulation types may block the movement of air but they are only effective if the insulation is installed in a way to prevent the air from moving around it. Batt or loose fill insulation does not stop air movement. Building sheathing may provide an air barrier but only if the joints between the sheathing sheets are properly sealed. Building wraps may provide an air barrier but you better check with the manufacturer to be sure. Some building wraps only provide a moisture barrier not an air barrier. The same is true of liquid applied membranes.
What is air infiltration?
Building air infiltration is defined as the air that enters or exits the building in unplanned, unmanaged ways, basically through holes in the building envelope. These holes may be made over time and result from the activities of maintenance people or remodeling or they may be the result of poorly detailed or executed construction joints. The interface between building facade materials, which is often the dividing line between the products of different sub-contractors, is a common location of poorly designed joints. The air barrier is often interrupted at these locations since neither the sub-contractors nor the
Air Infiltration Article
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general contractor take responsibility for the interface and the contract documents may be vague in detailing these areas also. In modern commercial buildings the facade by design may not be air tight. Facade systems using rain screen design principles do not stop the flow of air. Masonry systems have weep holes allowing air to circulate in the cavity behind the masonry veneer and allow moisture to drain out. With these and other facade systems the air barrier needs to be located behind the visible facade and must be continuously sealed to all other items penetrating the building envelope.
Why is managing air infiltration important?
A lot of effort and expense is put into making buildings comfortable, pleasant places to be. We expect certain things to just happen in our work places especially if those things are provided by the building owner as part of our lease agreements. Clean air and well controlled temperatures are two things we are supposed to get and they are both affected by unconditioned and undirected air blowing around our desks. Unmanaged air can have the following affects on the interior building environment. o o o o o o o o o o o Puts additional load on HVAC systems to condition the additional air. Is not filtered or dehumidified. Can bring in moisture and water potentially causing mold and other damage. Reduces the comfort of the interior space. Causes drafts. Carries dirt and pollutants. Can penetrate deep into the building space through ceiling spaces, wall cavities and other unintended plenums. Causes additional resources to be needed for cleaning and maintenance. Increases the use of HVAC systems driving up equipment and maintenance costs and the cost of utilities. Creates condensation. Causes discomfort and is distracting to the building occupants.
The Sources of air infiltration.
This list is pretty obvious, but, don’t overlook the potential for leaks through holes and joints in ductwork. And, remember that the air barrier in a building facade may actually be behind the materials that you see. Penetrations may need to seal to both the air barrier and the building facade. Sources of unmanaged air are leaks: o Within the building envelope. o Between facade elements. o Between facade and foundation and roof. o In the foundation and roof.
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o Around envelope penetrations: vents, pipes, window and door frames, etc. o Poorly weather stripped windows and doors. o In air intake or exhaust plenums and ducts.
Costs resulting from air infiltration.
The costs related to unmanaged air infiltration are going to vary with weather extremes. They will be less in mild climates and higher in places experiencing extreme cold or hot. If the only criteria used to measure the benefit of reducing or eliminating air infiltration is cost then there may be locations where the additional cost is not recoverable in a reasonable amount of time. However, if all of the items in the following list are considered then it may be worth it especially if you own the building and you and your employees work in it. o o o o o o o o o o o o Higher utility expenses. Higher capital cost for larger HVAC equipment. Higher maintenance cost for HVAC due to it running more. Building maintenance costs due to moisture in the walls and possible mold mitigation. Building cleaning costs due to dirt and pollutants carried into the occupied spaces. Tenant dissatisfaction and frustration. Lower employee productivity. Higher employee absenteeism and illness. Reduced building life. Reduced property value. Cost of retro-fitting and mitigating leaks is higher than additional construction cost if air infiltration was addressed during design and construction. Cost of finding the air leaks and fixing them.
What can be done?
New buildings have the potential to address this concern in the most proactive, efficient manner since no design or construction mistakes have been made yet. Here are some things that can be done in new buildings to keep inside and outside air separated. o Careful design and detailing of the building envelope, particularly between facade systems and transitions to the roof and foundation. o The air barrier needs to be uninterrupted. All penetrations need to be sealed and all joints in the barrier need to be properly overlapped, taped and sealed per manufacturer’s recommendations. o The air barrier needs to be properly sealed to door and window frames. o Insulation is not an air barrier due to where and how it is installed. Air will move through batt and loose fill insulation and the location of foam insulation usually does not seal off the places in a wall that will allow air to pass through.
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o Vents need to be sealed to the air barrier and any holes or joints in vent ducting needs to be sealed to prevent leaks. Exhaust vents, stove vents and dryer vents need dampers to prevent air from entering when the exhaust fan is not running. o Glazing system design, assembly and installation needs to contain and prevent air from moving through to the interior. o HVAC systems need to be designed to prevent them drawing air into the conditioned space. Air for combustion for furnaces and fireplaces or woodstoves needs to be drawn in directly from the outside. Air plenums need to be sealed from outside air. o Take care in the design process to avoid building in unintended “plenums” that outside air can follow into the building. o May need an air exchange system to provide proper ventilation. Unless a major renovation is being done, and all the occupants are moved out, it will be physically more difficult to plug air leaks in the building envelope of an existing building. All of the things listed for new buildings can be done to existing buildings but the value of doing certain things or replacing certain elements becomes more subjective when dealing with older buildings. The strategy to follow in existing buildings may look something like the following. o Perform tests to determine the volume of air that is infiltrating. o Identify location of air leaks and how to plug them. o Go after the big ones first, easy ones next and evaluate the value of plugging the rest of them. o Fixing existing buildings may entail replacement of windows and facade systems and HVAC and other mechanical systems. o Investigate the cost and inconvenience to the building occupants of eliminating air infiltration. o Investigate potential utility and maintenance cost savings. o Consider the increase in value to the building if this is done.
It takes a proactive approach by all members of the design/build team to effectively eliminate unmanaged air infiltration. Air infiltration needs to be addressed at the source. In other words the air needs to be kept out of the building. Once the air is inside the affects from the air are going to be felt and dealing with it is more expensive and difficult. The main thing to remember about air barriers is that to be effective they must be continuous. This means that the air barrier may be made up of several different facade elements which would include sheathing, building wrap, windows, doors, vents, pipes, etc. To prevent air leaks the transitions or joints between these elements have to be carefully detailed, installed, and sealed.
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In summary, do you fix the air leaks because it is cost effective and you will get to not only write off the cost of the maintenance but you will also realize savings in utility costs in the future, or do you do it because it is the right thing to do? Utility costs may fluctuate but in the long run they are going up. Fossil fuels are finite even if they remain abundant for our lifetimes and possibly our children’s lifetimes. The less we use now the longer they will last. Maybe investing to reduce usage because it is the right thing to do is justification enough.
Tom Kearns is the Detailing Manager for The Façade Group, LLC, a Portland, Oregon based building envelop consulting and detailing firm. He can be reached at (503) 243-2556; firstname.lastname@example.org.