Professional engineers and architects have legal responsibilities and liabilities as dictated by state statutes. Many of these responsibilities and liabilities are not generally understood by the public or various segments of the building industry until they lead to catastrophic events that are covered in the news.

These responsibilities and liabilities do not always come with full authority due to contractual terms between professional engineers, architects, and their clients. This is a growing challenge for professional engineers and architects in the consulting industry as well as the design-build industry. 

With respect to indoor air quality (IAQ) and indoor environmental quality (IEQ), the question of who has the authority for which decisions becomes important when the topics of responsibility and liability come into question during the design or construction process and/or litigation.


Terminology and Definitions

Many times, IAQ and IEQ discussions encompass a lot of talk based on opinions and perceptions with no foundation of understanding common industry definitions. 

ASHRAE’s website covers some of the terminology used in the industry but not all. It would make sense that all ASHRAE standards be required to only use terms that are defined within the ASHRAE terminology resource or otherwise provide a reference to a source that defines such terminology. It would also make sense that all ASHRAE standards use consistent terminology across all standards if for no other reason than to help the professional engineers who use those standards to “Keep It Defendable” (KID) in contract document specifications that reference these standards. 

Here are the ASHRAE terminology definitions for IAQ and IEQ: 

IAQ: “Attributes of the respirable air inside a building (indoor climate), including gaseous composition, humidity, temperature, and contaminants.”

IEQ: “A perceived indoor experience of the building indoor environment that includes aspects of design, analysis, and operation of energy-efficient, healthy, and comfortable buildings. Fields of specialization include architecture, HVAC design, thermal comfort, indoor air quality, lighting, acoustics, and control systems.”

There are other terms listed in ASHRAE’s terminology resource that are related to IAQ and IEQ, including acceptable IAQ, acceptable indoor environment, sick building syndrome, air contaminant, volatile organic compounds (VOCs), air cleaning, and others.


Codes and Standards

Engineering considerations concerning IAQ and IEQ are impacted by codes, standards, and design guidelines. Integrated designs complying with all codes, standards, and design guidelines take more than just looking at the HVAC ventilation requirements.

Complying with industry standards and design guidelines is a goal of many professional engineers. Some standards are being written in code language and adopted by the codes. Not all standards are required to be met; however, it’s generally good engineering practice to discuss the standards with clients and offer compliance as a desirable option. Complying with standards that are above the minimum code requirements likely will impact the cost of the building as well as have an IAQ and IEQ performance impact.

Three particular ASHRAE standards that engineers attempt to comply with are 55, 62, and 90.1, dealing with comfort, ventilation, and energy, respectively. It may not always be part of the scope of the design contract to comply with each of these three standards. Full compliance with all three may be possible in some applications, but that’s not always the case. It would make sense that when talking about IAQ, ASHRAE Standard 62 would take priority. However, when talking about IEQ, Standard 55 may take a higher priority depending on the design intent of the building. If ASHRAE 90.1 is the ultimate top priority, then ASHRAE Standards 55 — and even 62.1 (if not part of the local code) — may be sacrificed, which may impact both IAQ and IEQ. 

In all cases, in order to comply with the KID principle, it is good to have discussions about code, standard, and design guideline compliance at the beginning of every project. There must be a commitment by all team members on what the functional requirements are so that they are not subject to devalue engineering at any point in the design, bidding, or building processes.


Air Distribution

When it comes to minimizing energy as well as providing effective ventilation and comfort in a space, the supply air diffuser, which distributes the supply air to the space, is largely recognized as one of the most misused applied products in the HVAC portfolio. 

Many engineers and mechanical designers in the building industry have been taught to use the air diffuser performance data in manufacturers’ catalogs in a simplistic manner. A common approach has been to look at the 50-FPM terminal velocity distance and use that to select and size all air diffusers with a consideration of appearance and noise criteria (NC) levels. But, is that really all there is to it? Does this really meet the KID principle? Sometimes, yes; however, more often than not, it does not. 

This risk may be taken simply to speed up the design process. Documentation of air device selections is essential to show due diligence in compliance with codes, standards, and design guidelines to meet the functional requirements of each application.

There are supply air diffuser products on the market that provide greater variability in a VAV system’s airflow performance than others. These products generally have higher entrainment ratios that provide better total air movement in a space to meet Air Diffusion Performance Index (ADPI) performance criteria and ASHRAE 55 criteria for air distribution in a space. The plaque type diffuser is one such diffuser to consider, see Figure 1.

The ASHRAE Handbook chapter on air distribution has three primary air distribution selection device methods: appearance, flow rate, and sound data; lines of constant velocity and mapping; and comfort criteria. Do any of these directly correlate with the simple 50-FPM terminal velocity method used by many engineers in consulting firms and design-build contracting firms? If not, it may be worth reconsidering how something as seemingly simple as an air device selection meets the KID principle when IAQ and IEQ are part of the design criteria. The comfort criteria selection process in the ASHRAE Handbook involves ADPI, which is based on isothermal conditions. Consideration and adjustments for non-isothermal conditions for air device selections need to be documented.


Air Cleaning

Air cleaning is obviously an important factor in both IAQ and IEQ performance compliance. Air-cleaning media itself needs to be specified as well as the holding frames that can allow contaminated air to bypass the air-cleaning devices. Air cleaning, when discussed in context with IAQ, certainly has a greater scope than particulate capture. Understanding what air contaminants are in the outside air for ventilation as well as from recirculated inside air is important. 

Studies by the U.S. Environmental Protection Agency (EPA) have shown that, in some cases, inside air is more contaminated than the outside air used for ventilation. Air cleaning must take into account contaminants from the outside air as well as contaminants generated inside the building. One challenging question is what are the required measurable variables for the air exiting the air-cleaning device? Are these prescribed by codes, standards, design guidelines, building owner requirements, or any other reference source? If not, how clean is clean enough? If there are no measurable results, then who has the authority, responsibility, and liability for keeping the air clean?



When dealing with IAQ and IEQ, buildings with varying exhausts — such as hospitals and laboratories with fume hoods and commercial and institutional facilities with kitchen hoods —  can cause a building to enter negative pressure. Buildings like schools with woodworking shops that exhaust all the space’s air outside may need special air-cleaning technologies to recirculate the air. 

Makeup air, either conditioned or unconditioned, needs to be provided when exhaust fans are activated that are above and beyond the basic constant exhaust from toilets that may be adequately accounted for in providing code required ventilation air. Without proper makeup air, the air needed for the exhaust will indeed enter the building in an unfiltered manner through doors, windows, or the building envelope, which will impact IAQ and IEQ. 

Another consideration impacting IAQ and IEQ are unprotected entrances. The use of air curtains have proven to help offset unfiltered air infiltration through open doors. Vestibules, in general, simply don’t work when both doors are open. Even revolving doors bring unfiltered air into the building by virtue of their rotating air pockets. Air curtains are now allowed by code in lieu of vestibules because they offer greater effectiveness. Building positive pressure simply can’t and won’t offset blowing winds, as many architects and even engineers sometimes try to rationalize without actually calculating the pressure needed to offset a blowing wind.


Controls Matter

In general, it is not possible to control a specific variable that is not directly measured. There are many indirect control strategies that have been used for years to rationalize that minimum outside ventilation rates are being provided by air-handling units. However, over the entire range of operation of a building, these indirect control strategies are not always defendable over all conditions of the building’s operation. Engineers today, more than ever, must take into account direct measurement of metrics that are used to ensure IAQ and IEQ criteria are met. The building systems must be under control in all conditions of the building operation. The Keep It Simple (KIS) principle is good but should not be deployed at the expense of the KID principle. 

When it comes to air volume flow and air mass flow measurement for building pressure, ventilation verification, comfort control, or energy savings, there are many options on the market. The technologies include differential pressure, pitot tube, and thermal dispersion. There are pros/cons and features/benefits of each type, including cost, accuracy, installation location considerations, maintenance, independent testing, etc.

Sensors are also available to help measure and control levels of air contaminants. It is prudent to understand the risk of not providing direct measurement of the air contaminants of concern in any specific application. The measurement and control of surrogate variables are not the same as direct measurement of the variable of concern. The cost of defending a design that does not provide direct control due to a lowest-first-cost priority or devalue engineering to meet a budget may well be offset in legal defense costs if there is a problem and the owner sues for damages related to IAQ and IEQ caused by lack of direct measurement and controllability. 

Sensors and monitors can have dual and multiple sensing capabilities in one enclosure for convenience, including those that can be used for both CO and NO2 for facilities with vehicles, such as garages, maintenance facilities, etc. See Figure 2.


Commissioning and Tab

With respect to IAQ and IEQ, much can be said regarding commissioning and testing and balancing (TAB). Suffice it to say that both matter. The best engineering design intent, products, installation, and construction won’t matter if the building’s HVAC system and all systems in the building are not functioning together in accordance with the integrated design intent.

With regard to TAB, as related to IAQ and IEQ, the discussion could go on for many pages. There are many examples that can be shown where a TAB report showing numbers of readings does not fully explain and document the conditions in which the readings are taken. It is essential to document conditions and locations of all TAB readings as part of the commissioning process.


System and Equipment Selection Challenges

There are many types of HVAC systems and equipment on the market that have an impact on IAQ and IEQ. VAV systems sometimes get a bad rap for the wrong reasons, but those who truly understand how to design a high-performance VAV system use them effectively. Whether it’s VAV, CV, DOAS, VRF, chilled beam, displacement ventilation, PTAC, etc., engineers must be realistic in whether or not the system, products, and controls can meet the KID principle for IAQ and IEQ compliance.

Manufacturers of both package and custom air-handling units, and other equipment that impacts IAQ and IEQ, have challenges and opportunities ahead of them. Airflow measurement, air cleaning, coil cleaning, drain pans, cleanability, maintainability, efficiency, competitive cost, etc. all impact IAQ and IEQ. 

When it comes to outside air intakes, products such as louvers and louvered penthouses are designed to prevent moisture from entering a building. Moisture — whether caused by mist, drift, rain, or snow — that gets into an HVAC system or onto filters and impacts the quality of the air being delivered can impact the IAQ and IEQ in a building. Intakes that are designed with louvered penthouses can be subject to blowing wind and rain and snow entrainment from multiple exposures; therefore, water management is essential under the louvered penthouse.


High-Performance and Green Facilities

Looking at code minimums along with “high performance” and/or “green” initiatives in some applications may prove challenging for architects and engineers. These initiatives can be solely focused on energy or may include criteria for IAQ and IEQ. Some benchmarks may add risk to the design team if the benchmarks can’t be directly validated at the end of construction and during building operation. When IEQ embraces a comfort criteria, it can be a high-risk design if the comfort criteria can’t be proven during design and there are no options after construction for adjustments.


Integrated Design

IAQ and IEQ are indeed a complex challenge when fully integrated into the design, construction, and operation of a building. An integrated design that accounts for every aspect of IAQ and IEQ can be difficult, but not impossible, to build and prove with measurable metrics during building occupancy. Following the seemingly simple criteria that 80% of the occupants in a building agree they are comfortable at all times can be too subjective. To the professional engineer, this is beyond what is defendable when “experts” are called to give opinions. Noise, vibration, lighting, humidity, airflow, workspace ergonomics, seating, etc. are all IEQ factors that require measurable and verifiable metrics and involve every design discipline and construction trade.

Integrated design must take into account the project’s architectural goals as well as the engineering requirements. There are codes and standards that dictate some of the criteria for outside air intakes and exhaust locations and separations thereof. There are some buildings that may require more than just meeting a basic code minimum requirement of separation distances due to wind conditions and the contaminants being exhausted. Even analysis by wind consultants may not be applicable to all product types. When it comes to modeling in a wind tunnel, the exhaust profile from all fans, such as induced draft fans, may not be truly modeled when it comes to the minimum outlet velocity versus the average outlet velocity of induced draft fans. It is a risk to ignore this factor and a liability for the engineer of record specifying the fans if this is not disclosed by the wind consultant.

Green roofs, which have contaminated dirt and plants, have been used in many recent designs and retrofits. Plants often carry pollen and may require chemicals to control insects and plant diseases. Outside air intakes near green roofs, just like outside air intakes near the ground, need to take into consideration contaminants that may enter the building ensure appropriate air cleaning is provided for complete integrated design.

Another aspect of integrated design is the specification of building interior materials for both architectural and interior designs. Many manufacturers, but not all, that make building components have products that are free of contaminants, such as VOCs, but these need to be clearly specified. Architects, interior designers, and engineers are generally not experts on contaminants, so it may be necessary to have a specialty consultant, such as an industrial hygienist, to help with those specification criteria. Both new and retrofit buildings must take into consideration the emission rates of contaminants and possibly have time in the project construction to properly ventilate the building to allow the dilution of the contaminants that are part of the off-gassing process.

Some codes and standards allow both mechanical and natural ventilation; however, there are no real criteria with natural ventilation on the ventilation effectiveness as there are for mechanical ventilation. This can be a risk for architects who do not truly analyze the ventilation method for true effectiveness and don’t employ a professional engineer to do this analysis. The design may meet the letter of the code but not the full intent of the code and standards with respect to ventilation effectiveness. 

Noise control and sound levels impact IEQ and may be costly to fix if they’re not properly accounted for in the design from the beginning. Sound from fans and other HVAC products needs to be considered as well as vibration. Architectural materials in walls and ceilings can be specified with ceiling attenuation class (CAC) and sound transmission class (STC) values, respectively. The mechanical engineer needs to realize the catalogued data of the air device is based on an industry standard for a room’s ceiling, walls, and flooring as well as the air inlet into the air supply diffusers. Engineers need to adjust these basic catalog values to be specific for a room’s actual construction.

The building envelope is a major component that impacts the HVAC design and, thereby, IAQ and IEQ. Thermal and vapor barrier performance must perform in accordance to what the architectural design intent is and to what is used in the design of the mechanical systems. The fenestration in the building envelope is not only a factor in the thermal load in a building, but it is also a factor in lighting levels and energy use. There are window treatments on the market that can be applied to or integrated with fenestrations to control the lighting level and thermal loads that impact IEQ.


By Whose Authority?

Professional engineers as well as professional architects have an obligation and a duty that relates to the design of buildings. And while they have that responsibility and liability, they don’t always have the full authority to make the necessary decisions. This is part of the risk taken on in the consulting business and design-build industry for companies that offer professional architectural and engineering services. Complying with current codes and standards that relate to and impact IAQ and IEQ is becoming more of a risk. It doesn’t take long to research IAQ and IEQ discussions to not only find differences of opinions but also biased opinions from those who have a vested and profit-driven interest in the decisions made by codes, standards, and design guide publication organizations. Terms as seemingly simple as acceptable, optimal, adequate, and majority can impose an undefendable risk if they’re not clearly, concisely, completely, and correctly defined in the contract documents.

The authority, responsibility, and liability related to IEQ and IAQ decisions should always be discussed in advance. Decisions regarding lowest first cost, project budgeting, and the process of devalue engineering (cost cutting) by anyone other than the professional engineer, who is the legal engineer of record according to the state statutes, can be in conflict to those who have the IAQ/IEQ decision-making authority.