Combating building pressure at the door

April 27, 2018

All images courtesy Allegion U.S.

By Alan D. McMurtrie, DAHC
Building pressure is an invisible, pervasive threat that puts projects at risk—and it all starts at the door. Accessibility, life safety, and energy efficiency are concerns in all buildings, but uncontrolled pressure can increase these hazards. The first line of defense begins with selecting the correct door closer.

Closers are commonly used in commercial structures to ensure doors are shut and securely latched, as well as to reduce airflow through the building. When the correct closer is in place, it can reduce the potential concerns caused by pressure differentials. To understand how building pressure can put buildings at risk and how closers can mitigate it, one should first explore what causes the phenomenon.

Building pressure causes
Building pressure is caused by a difference in temperature or pressure between two spaces separated by doors. As air pushes into or out of a building—moving from an area of high pressure to one of lower pressure—it exerts incredible amounts of force on the doors and can prevent door closers from properly functioning.

Sometimes referred to as stack pressure, these significant pressure differentials often occur between the inside and outside of a building, but can also create problems between adjoining rooms or wings of a facility. Corridors, atriums, and stairwells are particularly at risk. The more extreme the difference between interior and exterior temperatures, the greater the amount of pressure that will exist inside, predominantly in multistorey buildings.

Pressure differential is created primarily by three forces: wind, temperature, and the facility’s HVAC system.

Air is typically forced into a building on the side facing into the wind (i.e. the windward side), and pulled out on the side sheltered from the wind (i.e. the leeward side). Strong winds can create significant airflow through a building, dramatically increasing the amount of pressure in one area compared to another. The structure’s shape can also create swirling winds or irregular wind pressures that impact the amount of negative or positive building pressure. Positive pressure exists when the pressure inside a building or space is greater than the pressure on the outside. It can be beneficial in areas such as patient rooms, where it limits exposure to any outside germs or contaminants.

Negative pressure exists when the pressure inside a building or space is less than the outside pressure. This tends to make outswinging exterior doors difficult to open.

Figure 1: If the outdoor temperature is lower than the indoor temperature, this can create high negative pressure within a building’s lower levels and high positive pressure in the upper levels. This pulls cold outdoor air in at the lower levels and pushes heated indoor air out at upper floors.

An extreme difference between interior and exterior temperatures can cause building pressure in a facility, a phenomenon sometimes referred to as the chimney or stack effect.

In parts of Canada, issues can arise with hotter temperatures in the summer, meaning stack pressure can occur in the building when the air-conditioning is going. This can impact not only perimeter doors, but also stairwells.

A significant amount of airflow can be created in such areas, where the lower density of warm air causes it to rise and displace cooler air. This also occurs due to the difference in air density between the interior of the building and the exterior.

For example, if the outdoor temperature is -1.11 C (30 F) and the indoor temperature is 21 C (70 F), this can create an excessive amount of negative pressure within the lower levels of the building, and a correspondingly high amount of positive pressure within the upper levels. The pressure difference pulls the cold outdoor air in at the lower levels and pushes the heated indoor air out at the upper floors. When it is warmer outdoors than indoors, the opposite happens, as explained in Figure 1.

HVAC systems
As buildings consist of numerous interconnected rooms of varying sizes and pressures, HVAC systems must attempt to equalize the temperature and pressurization of each by using fans to circulate and exhaust the air. Air will naturally flow from high-pressure areas to lower-pressure ones, meaning these systems are often used in highrise buildings to deliberately increase pressure within the lower levels of stairwells, helping to keep them free of smoke in the event of a fire.

While it may sound like a fairly benign problem, building pressure can cause serious issues within a facility, resulting in safety and security risks, code violations, as well as increased energy costs. Specifying an effective door closer can help combat these risks.

Door closers and building pressure
The effects of building pressure are known throughout the industry, but determining which openings will be affected—if any at all—can be tricky. It neither happens on every opening, nor in every building. There is no perfect solution, as it can be difficult to know how great the pressure differentials will be until the building is completed.

While nobody can know for certain how building pressure will affect each opening, early preparation is possible. This is why building designers strive to be proactive during the design phase. Architects want to do anything they can upfront to address issues before they become problems. For instance, when looking at plans, one might notice an exterior door is positioned in a manner allowing the north wind to “grab” it as it opens. The architect could change the direction of the door—however, what about cases when the direction cannot be changed, or repositioning would not change the impact of building pressure? That is where the correct door hardware can make a world of difference.

Architects and building designers should be aware of potential issues upfront and plan for what might need to be addressed later. Will the building have pressurized stairwells? Is there high wind in the area? Will the building sit atop a hill? How often will it be used? Who will use it—children or adults? It is also important to think about the climate. Areas with extreme temperatures are much more susceptible to higher pressure differentials.

All these factors should be considered during the design phase of the project, as they help indicate what type of closer is needed to overcome the likelihood of building pressure. When it has been determined an opening will be affected, it is best to specify a heavy-duty closer or auto-operator. A heavy-duty door closer helps control the door, especially when shutting. This type of closer has a larger piston and spring than a typical closer. An automatic operator controls both the opening and closing of the door without the need for physical contact. Another recommended product is an overhead stop to protect the door as it opens.

If the opening is an accessible opening, an auto-operator is required. In some cases, this type of hardware can be considered even if the opening is not required to be accessible. If the door is going to see a high level of pressure or abuse, auto-operators are specified for ease of use and convenience. They cost more upfront, but specifying an effective closer at the start is more economical than installing one down the road. It both saves clients the hassle, and can also result in long-term savings.

Building pressure risks
Building pressure can cause various problems related to doors, affecting accessibility, security, and energy efficiency unless an appropriate door closer is used.

There is a struggle between maintaining a properly latched door and accessibility. If a building has too much positive pressure, it can result in doors unable to close and latch securely. Facility managers typically try to address this by adjusting the door closers or replacing them with larger ones. While this might do the trick, installing an overly large closer can result in serious code violations.

Interior nonfire doors in a barrier-free path of travel should be operable with 22 N (5 lb) of force or less. However, in an effort to compensate for building pressure, closer power is often increased to enable the door to close and latch. The door will have enough force to shut, but the larger closing torques may reduce accessibility, restricting access for elderly or disabled occupants. Additionally, when pressure differential is relatively large, a door closer with low opening force may comply with barrier-free requirements, but may not be able to overcome the resistance and fully latch the door, allowing it to remain open. A solution to this is to specify a barrier-free door operator that both opens the door automatically for those that need assistance and closes and latches the door.

Doors unable to latch securely are of particular concern in exit stairwells, which are subject to the most extreme effects of building pressure due to their construction. The doors to these exit enclosures are designed to act as barriers, preventing the spread of smoke and fire throughout a facility and maintaining a safe means of egress. However, if a door cannot latch securely because the closer cannot overcome the pressure differential, occupants may not be able to evacuate safely, and the damage from the smoke and fire could be more extensive.

There are limitations on opening force for both accessibility and egress. Additionally, fire doors are required to have enough closing force to reliably close and latch the door. It is important to be cautious when installing a closer with a larger spring size or increasing the closer speed to overcome stack pressure. These methods may solve the problem, but frequently result in openings that no longer meet opening force limitations.

Additionally, closer adjustment is often performed improperly and results in a door closing too quickly when the pressure difference is not impacting the opening, causing excess stress and wear on the hinges, latching hardware, frame, and the door itself. This also creates the potential liability of someone being injured by an uncontrolled slamming door.

From multi-use facilities to hospitals to residence halls, security is top of mind throughout the design process of many projects. Design/construction professionals may follow codes and guidelines, specify the best door hardware, and plan for access control solutions, only to find there is an invisible force working against the facility—building pressure.

When a door is unable to overcome the pressure within a building, one might notice it is left ajar. This is especially concerning at a perimeter door, where unwarranted guests can enter the facility. This means the building is at risk for unauthorized access, hardware damage, and even injury.

Even openings with the most advanced access control systems can fall short when faced with building pressure. These electronic solutions are designed to enhance security, but for them to function effectively, the closer must completely shut and latch the door. It is counterproductive to have electronic access control solutions on a door with a closer that does not work.

In addition to the security features, a benefit of this technology is users can efficiently monitor doors from afar, not needing to manually inspect the openings. If a door does not properly close, users will be notified with alarms. They then must send someone out to the door to verify whether it has been breached or simply failed to close.

Again, one way to overcome this issue is to adjust the spring size of the closer. However, if the valve is modified to control speed, it can cause other problems. As mentioned, a door closer adjusted to overcome high pressure differentials during the warmer months may slam shut as temperatures start to cool and pressures lower. An effective closer not only properly shuts a door when pressure is high, but also prevents the door from slamming when the differential is not impacting the opening. Any full-feature Builders Hardware Manufacturers Association (BHMA) Grade 1 surface door closer can effectively accomplish this by controlling swing speed, latch speed, and back check.

Energy efficiency
Door closers combat building pressure’s effects on energy costs by decreasing airflow through an opening and improving total cost of ownership. Specifying the correct door closer reduces airflow and energy loss through exterior openings of a building and results in long-term energy savings.

Buildings are designed to allow a small amount of airflow to exhaust from the structure in order to keep dust, smoke, and odours outside. However, this process requires the HVAC to effectively overcome the fluctuations in pressure caused by wind, outside temperature, building design, and various other factors. If the system is unable to do so, it can lead to a high pressure differential, which may ultimately result in higher energy costs, lowered indoor air quality (IAQ), building deterioration, and door hardware damage.

Properly closed openings also prevent the infiltration of warm, humid air into a facility during warmer months. If a door is left ajar, the interior becomes subjected to conditions ideal for mould growth, poor IAQ, and structural deterioration. In colder months, similar problems can develop, as positive pressure may force warm air into the building envelope, causing moisture to condense on cold surfaces inside the building.

“Energy Cost Savings Using an Effective Door Closer,” a recent joint study conducted by Purdue University, the Chinese University of Hong Kong, Tianjin University, and this author’s door hardware manufacturing company examined the potential heating and cooling energy cost savings from using an effective door closer. Using the closer under different pressure differentials in different climate zones with a spring setting of Size 1, the study found by installing an effective closer on exterior doors, companies could save as much as $2134 per door in annual heating and cooling costs.

The study also found as pressure differentials increase, so do facility costs. Areas with extreme climates, like Edmonton, will see the highest potential for savings. The larger the temperature gap, the greater the indoor-outdoor pressure differential—resulting in greater airflow through the door. More energy is needed to condition the additional air flowing through the opening and, therefore, energy costs will be higher.

Similarly, the U.S. National Institute of Standards and Technology[4] (NIST) reported annual heating and cooling energy costs could be reduced by three to 36 per cent, depending on the climate zones, if the target airtightness levels were achieved. A door closer that securely shuts and latches the opening can help significantly.

Considering the impacts of building pressure early in a project can substantially improve long-term savings. By specifying an effective door closer upfront, architects can reduce airflow throughout a facility to improve sustainability, energy costs, and the building’s longevity, as well as overcoming safety and security risks.

Alan D. McMurtrie, DAHC, is a certified, distinguished architectural hardware consultant who is a member of the Door and Hardware Institute (DHI). He has 32 years of experience in the openings industry—specifically, with specifying architectural hardware for design professionals. Successful healthcare projects McMurtrie has specified in Ontario include North Bay Regional Hospital, Sudbury Regional Hospital, Meno Ya Win Health Center, and Toronto Rehabilitation Institute. McMurtrie can be reached via e-mail at[5].

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