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Summary and critique of "LEED" Building Design & Construction Reference Guide, v4

Jonathan Ochshorn

compare with Version 2.2 NC and Version 3.0


Following is my summary and critique of the USGBC's LEED Building Design & Construction Reference Guide, v4. Commentary on the Reference Guide can be found in these red boxes, sometimes within each of the chapter links immediately above, but also in my summary and critique of the prior versions: Version 2.2 NC and Version 3.0.

7. Indoor Environmental Quality (IEQ)


IEQ Prerequisite 1: Minimum indoor air quality performance

Intent: Like the title says — minimum IAQ. The idea is to dilute pollutants that would otherwise make indoor air unhealthy. On the other hand, too much outdoor air can increase the energy needed to condition the air, so a "balance" is desired — use just enough fresh air to keep people productive, but no more.

Requirements: There is a "ventilation" as well as a "monitoring" requirement, both of which are based on the type of ventilation provided — i.e., mechanical or natural.


  1. For mechanically ventilated spaces, satisfy ASHRAE Standard 62.1-2010 (Sections 4-7 with errata); non-U.S. projects can meet other criteria based on European standards.

  2. For naturally ventilated spaces, conform to the appropriate sections of ASHRAE Standard 62.1-2010, and make sure that natural ventilation is a viable option, per CIBSE AM10 (March 2005 version).


  1. For mechanically ventilated spaces, install a device that can actually measure the outdoor air intake.

  2. For naturally ventilated spaces, install all sorts of devices: for example, there must be alarms that go off if openings required for natural ventilation are not open when the space is occupied; and there must be CO2 detectors in each thermal zone. Also note that the new ASHRAE standards referenced here require mechanical ventilation in some cases — i.e., it is not always possible to use only natural ventilation.

IEQ Prerequisite 2: Environmental tobacco smoke (ETS) control

Intent: Reduce impact of ETS directly on occupants, but also on ventilation air and indoor surfaces.

Requirements: There are two cases, the first for all buildings, and the second for residential only. For Case 1, there is only one option: No smoking is allowed in the building or within 25 ft. of openings/air intakes; and appropriate signage must be provided.

For Case 2 (residential), there are two options: Either prohibit smoking, or prohibit smoking only in common and exterior areas, while compartmentalizing all residential units (basically sealing each unit from all others).

[From Version 2.2 critique] This is a bit strange to have in a sustainability guideline, since it is impossible to assess its impact. Nothing prevents the current building owner, or a new owner, from changing a smoking policy. On the other hand, smoking is already prohibited in many buildings by state or local law.

CDC smoking map
[Feb. 26, 2021 update: see this CDC website for interactive maps and other information on state-by-state smoking laws.]

IEQ Credit 1:Enhanced Indoor Air Quality Strategies (1-2 points)

Intent: Improve indoor air quality (IAQ) and thereby improve comfort, health, and productivity.

Requirements: There are two nonexclusive options, each worth 1 point, so that a total of 2 points may be achieved.

Option 1 has several requirements, depending upon whether the building is mechanically or naturally ventilated (or is a "mixed-mode" building with both mechanical and natural ventilation). In all cases, the building must have a 10-foot long entryway in which grates or grilles, or comparable systems, are deployed to trap dirt and other particulate matter so that it does not enter the building. For mechanically-ventilated spaces only, prevent cross-contamination (of hazardous gases or chemicals) into adjacent spaces by exhausting the contaminants in such a way that negative pressure exists within the space; also, install self-closing doors. For such mechanically-ventilated spaces, use particle filters or other devices that achieve a minimum efficiency reporting value [MERV] of at least 13 on any ventilation supply stream that contains outside air.

Naturally ventilated (or mixed-mode) buildings must meet standards in Chartered Institution of Building Services Engineers (CIBSE) AM10 March 2005 for "Natural Ventilation in Non-Domestic Buildings," Section 2.4.

Option 2 also distinguishes between mechanical and natural ventilation. In all cases, the building design can choose to limit the quantity of all pollutants regulated by the National Ambient Air Quality Standards (NAAQS) based on either an allowable annual average or, if a pollutant has no annual average standard, an 8- or 24-hour average, or a "rolling" 3-month average. Such pollutants originate exterior to the building, so this requirement aims to limit the entry of such exterior pollutants into the building.

For mechanically-ventilated buildings, one can also choose to increase the outdoor air by 30% above the minimum required in the prerequisite.

[From Version 2.2 critique] The idea that increased ventilation rates necessarily improve indoor air quality is however — and paradoxically — questionable. Joseph Lstiburek writes: "My insider's perspective (on Standard 62.2 at least) is that there is a lot of mileage to be made by scaring people about underventilation, and folks are rising to the occasion. Unfortunately, overventilation in hot, humid climates has led to more indoor air problems due to mold resulting from part-load issues than underventilation anywhere else... Doesn't anyone at the U.S. Green Building Council know anything about energy and part-load humidity?" (ASHRAE Journal, August 2008, p.64).

[July 8, 2014 update: See also Martin Holladay's Discussion of ventilation rates and human health and Overview of the ventilation debate.]

[April 8, 2015 update: See also this report on Clarkson University researchers studying possible links between reported hauntings and indoor air quality: i.e., the possible relationship between hallucinations caused by certain molds and sightings of ghosts!]

Mechanically-ventilated buildings can also choose to either provide CO2 monitors in all "densely occupied spaces" that trigger some sort of response when the CO2 is 10% higher than the system's setpoint — where the setpoint is determined based on ASHRAE 62.1 2010 (Appendix C) — or, where there may be other (non-CO2) contaminants in a space, provide some system that monitors such contaminants and also make a plan to reduce such contaminants in the first place. This latter alternative also applies to naturally-ventilated spaces.

Naturally-ventilated buildings can also calculate room-by-room airflow patterns in order to optimize ventilation, based on CIBSE AM10, Section 4.

In other words, the Option 2 point can be achieved by meeting the standards for any one of the various choices listed, depending upon whether the building is mechanically or naturally ventilated (or mixed mode).

IEQ Credit 2: Low-emitting materials (1-3 points)

Intent: Improve indoor air quality (IAQ) and thereby improve comfort, health, productivity, and "the environment" based primarily on control of volatile organic compounds (VOCs).

Requirements: For new construction, there are two options. Within these options, LEED distinguishes between interior and exterior materials, based on their position relative to the building's waterproofing membrane (for interior materials) or the building's "primary and secondary weatherproofing system" which includes both waterproofing membranes and air/water barriers (for exterior materials). The waterproofing membrane is considered part of the "exterior," along with everything outside that membrane.

In Option 1, LEED identifies 6 categories of materials, each with their own compliance standards. For projects without furniture, meeting the standards for 2 categories gives you 1 point; 4 categories gives you 2 points; and 5 categories gives you 3 points. For projects with furniture, an additional category must be satisfied to achieve the same number of points (i.e., 3, 5, and 6 categories respectively).

LEED provides a "Table 1" showing the various categories, their "threshold" limits for compliance, and their emissions/content requirements (the latter is not shown below):

Interior paints applied on siteat least 90% of products in this category (measured by volume) must comply for emissions; 100% for VOC content
Interior adhesives/sealants applied on siteat least 90% of products in this category (measured by by volume) must comply for emissions; 100% for VOC content
Flooring100% must comply
Composite wood100% of products in this category — not covered within other categories — must comply
Ceilings, walls, insulation100% must comply
Furniture, if included in scope of workat least 90% of products in this category (measured by volume) must comply

In Option 2, LEED claims to create 6 interior categories, although only the following 5 categories are listed: flooring, ceilings, walls, insulation, and furniture (where furniture is only included if it is part of the scope of work).

These represent "assemblies," so they include all paints, coatings, and adhesives/sealants that may or may not be part of the assembly; and all such things must be evaluated for compliance.

At this point, the guidelines become a bit confusing: In Equation 1, LEED defines the total percentage compliance as being equal to the average percentage compliance of the individual categories (either with or without furniture). In Equation 2, LEED defines a "system percentage compliance" (for everything except furniture) as the total compliant surface area of all "assembly layers" divided by the total surface area of all such layers. So, for example, if there are 80 square feet of compliant layers and 100 total square feet of layers, then the system percentage compliance would equal 80%. But there's more: only percentages between 50 and 90 percent are taken literally; anything above 90% is taken as 100% and everything below 50% is taken as 0% compliant.

Finally, in Equation 3, LEED creates a furniture percentage compliance based on ANSI/BIFMA standards and using cost as the metric: half the cost of compliant furniture complying with section 7.6.1 plus the full cost of furniture complying with section 7.6.2 divided by the total cost of all the furniture (multiplied by 100 to get a percentage value).

Note that these equations are actually executed in reverse order in Option 2: first, the percentage compliance of the assemblies is computed based on Equations 2 and 3; then these values are inserted into Equation 1 to get the total percentage compliance. Once that final percentage is computed, points are allocated as follows: 1 point for 50-70% compliance; 2 points for 70-90% compliance; and 3 points for 90% or greater compliance.

Compliance is based on a "general emissions evaluation" per the California Department of public Health (CDPH) Standard Method v1.1-2010, except that materials known to be VOC-free need not be subjected to any particular test. There are additional standards to insure that "wet-applied" products do not endanger workers on site.

It's always useful to remind readers that the health of workers installing such products and the health of building users may still be compromised in LEED-certified projects, since compliance with this, or any, credit is optional. One wonders about the seriousness of an environmental standard that permits high levels of VOC emissions in a certified building.

IEQ Credit 3: Construction indoor air quality management plan (1 point)

Intent: Improve indoor air quality (IAQ) in relation to potential problems originating with construction and renovation processes.

Requirements: Develop and implement a plan consisting of the following 4 elements:

  1. Comply with the Sheet Metal and Air Conditioning National Contractors Association (SMACNA) IAQ Guidelines for Occupied Buildings under Construction, 2nd edition, 2007, ANSI/SMACNA 0082008, Chapter 3.

  2. Avoid potential problems, including mold/mildew, by protecting construction materials and assemblies from water.

  3. Don't use air-handling equipment intended for occupancy during construction, unless it is protected with approved filters that are replaced immediately before occupancy. A MERV rating of 8 is required for any such filters.

  4. No smoking allowed during construction.

IEQ Credit 4: Indoor air quality assessment (1-2 points)

Intent: Reduce IAQ problems due to construction process itself, while protecting occupants and construction workers.

Requirements: Two options are available. Either: (1) For 1 point, flush out the building by ("path 1") providing new filters just before occupancy and supplying 14,000 c.f. outdoor air per sq.ft. floor area at internal temperature of min. 60 degrees and max. relative humidity of 60%; or ("path 2") spread out the flush-out air before occupancy (3,500 c.f. outdoor air per sq.ft. floor area) and during occupancy (greater of 0.30 cfm per sq.ft. of building area or design min. rate per Prerequisite 1) beginning each day 3 hours early until the total outside air volume of path 1 is reached; OR (2) Actually test the air per EPA Compendium of Methods for the Determination of Air Pollutants in Indoor Air as modified in these LEED guidelines. Then flush-out only as needed to bring contaminated areas into compliance, as follows:

ContaminantMaximum Concentration
formaldehyde27 ppb
particulates (PM10)50 micrograms per m3
ozone (only if building is in EPA-defined non-attainment area)0.075 ppm
total VOCs (TVOCs)500 micrograms per m3
target chemicals per CDPH Standard method v1.1 Table 4.1, excluding formaldehyde5see standard for guidelines
CO9 ppm and no more than 2 ppm above outdoor levels

[From Version 2.2 critique] The LEED rationale for improving IAQ is that increasing worker productivity translates to "greater profitability for companies…" at least relative to those businesses that prefer to save energy by supplying stale air to building occupants. This trade-off between energy cost and indoor air quality is made explicit elsewhere in the LEED guidelines, so that the claim here that IAQ improvements, in and of themselves, lead to "greater profitability" is contradicted by the admission that the added costs of heating and cooling fresh air may outweigh any productivity gains. The idea that increased IAQ necessarily leads to greater productivity is also questionable, especially where workers do not get paid sick leave (this includes approximately half of all full-time private sector workers in the U.S.). When sick workers don't get paid, productivity (a measure of output per amount invested) doesn't necessarily suffer, since either remaining workers will pick up the slack (actually increasing productivity), or temporary workers will fill in (leaving productivity unchanged).The suffering of workers — admittedly increased by conditions of poor air quality — cannot simply be equated with reduced productivity of capital.

Even where a certain allowance is made for sickness (e.g., company policies or legislation mandating a certain number of "sick days"), this simply becomes the new "baseline" factored into business calculations; in this context as well, improved worker health due to improved IAQ does not necessarily translate into increased rates of output (productivity). Studies that purport to show productivity gains due to increased indoor air quality are often flawed, in that they do not actually measure productivity, but rather measure health improvements which are then carelessly extrapolated into productivity claims. For example, given a potential reduction in respiratory illness of 9% to 20% based on improved indoor air quality, one scholarly study [PDF] concludes that "16 to 37 million cases of common cold or influenza would be avoided each year in the US. The corresponding range in the annual economic benefit is $6 billion to $14 billion." This so-called "benefit" is calculated by multiplying the average wages of the workers studied (apparently $375 per sickness) by "16 to 37 million" incidents of colds or flu per year. But it is not at all clear that this "benefit" is lost, or, if it is lost, who the loser is: to repeat the point made above, when sick workers are not paid, productivity may actually increase (as fellow workers pick up the slack), or at least stay more or less the same as replacement workers are hired.

Another criticism of productivity claims — according to Anne Whitacre's letter in the February 2008 issue of The Construction Specifier — is that "worker productivity goes up when employees move to a new office space, but that the result is often short-lived." She concludes that "since most green buildings have been around for less than five years, any long-term studies of costs and productivity are simply not yet available." I haven't been able to independently confirm this claim.

Practices that damage worker health have always been perfectly compatible with both productivity and profitability (see, for example, this NY Times Op Ed by Susan J. Lambert from Sept. 19, 2012). It is always state intervention (40-hour week, child labor laws, and so on) that establishes the baseline conditions for acceptable damage to worker health, compatible with growth of the economy as a whole. While it may be true that competition for the highest-level elite workers impels owners in such industries to offer higher-quality interior environments, low levels of indoor air quality for the rest of the work force threaten neither productivity nor profitability.

IEQ Credit 5: Thermal comfort (1 point)

Intent: Improve thermal comfort conditions and thereby improve comfort, health, and productivity.

Requirements: There are two alternative design options — either complying with ASHRAE Standard 55-2010 (Thermal Comfort Conditions for Human Occupancy) or ISO and CEN Standards — and a requirement for thermal comfort controls that are available for a minimum of 50% of individual occupant spaces and 100% of all multi-occupant spaces. Controls must be provided for all individual spaces, even if not individually-operated controls.

typical office floor with individual controls on supply air

Example of variable volume air distribution on typical office floor

LEED defines thermal controls in a rather flexible manner. Only one of the following parameters need be controlled to qualify: air temperature, radiant temperature, air speed, or humidity.

IEQ Credit 6: Interior lighting (1-2 points)

Intent: Improve interior lighting conditions and thereby improve comfort, health, and productivity.

Requirements: There are two options worth 1 point each, one for control and the other for quality of lighting, both of which may be achieved for a total of two points.

Option 1 requires that a minimum of 90% of individual occupant spaces have individual controls that can be set at on, off, or some intermediate position. Also, multi-occupant spaces must have similar controls with switches in the actual space.

Option 2 concerns "quality" and requires that at least 4 of the following strategies are implemented:

  1. Allowing for some exceptions, light fixtures must have a luminance of less than 2,500 cd/m2 between 45 and 90 degrees from nadir. The image below, taken from MY LED LIGHTING GUIDE, illustrates how such angles are measured:
    nadir in a light fixture

  2. Allowing for some exceptions, light fixtures must have a color rendering index, or CRI, of at least 80. This coincides with the EnergyStar recommendations for accurate color replication in homes.

  3. At least 3/4 of the "connected lighting load" must have a rated life expectancy of 24,000 hours.

  4. Direct-only overhead light fixtures can be used for no more than 1/4 of the connected lighting load.

  5. Surface reflectance values for at least 90% of the occupied floor area must satisfy these criteria: ceilings = 85%; walls = 60%; and floors = 25%.

  6. Furniture, if included in the scope of work, also has to meet certain reflectance standards: 45% for work surfaces; and 50% for movable partitions.

  7. The ratio of average (solid) wall surface illuminance to average work plane illuminance cannot exceed 1:10 for 75% of regularly occupied floor area, while also either satisfying the prior two strategies (Nos. 5 and 6), or just satisfying the requirement for surface reflectance of walls in No. 5.

  8. The ratio of average (solid) ceiling surface illuminance to average work plane illuminance cannot exceed 1:10 for 75% of regularly occupied floor area, while also either satisfying Strategies Nos. 5 and 6, or just satisfying the requirement for surface reflectance of ceilings in No. 5.

IEQ Credit 7: Daylight (1-3 points)

Intent: Reduce electric lighting loads, reinforce circadian rhythms, and "connect" building users to the outdoors.

Requirements: There are two options, as follows:

Option 1: Spatial daylight autonomy (sDA300/50%) must be at least 55% for 2 points or 75% for 3 points. sDA measures the percentage of floor area that exceeds a base foot-candle value at least 50% of the time (time being basically constrained to business hours). This is validated using computer modeling over a period of 1 hypothetical year using a 2-foot (or smaller) grid 30 inches above the floor. Also show that annual sunlight exposure (ASE1000,250) is no more than 10%. ASE measures the amount of direct sunlight incident on glazing surfaces; it is limited because such direct sunlight generally will have a negative impact on air conditioning costs, and also will have a negative impact on light-sensitive artworks, or even humans.

Option 2: Alternatively, but again using computer simulation, show that illuminance levels will be between 300 and 3,000 lux at 9:00 am and 3:00 pm on or about the fall and spring equinox (i.e., the clearest computer-simulated day within 15 days of Sept. 21 and March 21) for 75% or 90% of regularly occupied floor area (gaining 1 or 2 points respectively).

In addition to complying with either option, glare-control devices must be provided everywhere.

IEQ Credit 8: Quality views (1 point)

Intent: "Connect" building users to the "natural" outdoors by giving them "quality" views.

Several of these words are shown in quotes, as they seem either misleadingly metaphorical ("connect"), impossible to define ("natural"), or so subjective as to be useless ("quality").

Requirements: There must be a direct line of sight, through glazing, to the exterior available from at least 75% of all regularly occupied floor area. In addition, 2 of the following 4 view types must be available:

  1. Views in at least two directions through glazing such that the angle between the two lines of sight is at least 90 degrees.

  2. Views of at least 2 of these 3 things: a) flora, fauna, or sky; b) movement; or c) objects 25 feet from the glazing.

  3. Views of unspecified character that are "within the distance of three times the head height of the vision glazing." [I'm not sure what this means.]

  4. Views based on a "view factor" of 3 or more per a LEED-cited study of office worker performance.

Actually, outdoor views can be indoor views, if the indoor view is of an atrium — but in such cases, the atrium views can only satisfy 30% of the required floor area.

IEQ Credit 9: Acoustic performance (1 point)

Intent: Improve acoustic design and thereby improve communication, health, and productivity.

Requirements: A number of noise issues need to be addressed to satisfy this credit:

  1. HVAC equipment noise must be reduced per the 2011 ASHRAE handbook dealing with HVAC Applications (Chapter 48, Table 1). Measurements are not modeled, but actually made with a sound level meter.

  2. Various spaces must be sound-isolated from adjacent spaces according to the "sound transmission class" (STC) ratings found in this credit's Table 1:

    Spaces that are adjacent to each otherSTC
    Residential room (or hotel/motel room)Residential room (or hotel/motel room)55
    Residential room (or hotel/motel room)Corridor or stair50
    Residential room (or hotel/motel room)Retail space60
    Retail spaceRetail space50
    Standard officeStandard office45
    Executive officeExecutive office50
    Conference roomConference room50
    Office or conference roomCorridor or stair50
    Mechanical equipment roomAny occupied area60

  3. Reverberation time within spaces must be controlled according to this credit's Table 3. For example, the T60 reverberation time (known as "TR60" — the time in seconds for the "average" sound in the room to become 60 decibels less) at 500, 1000, and 2000 Hz for office building conference rooms must be less than 0.6 seconds.

  4. There are a few requirements for those auditoriums and large conference rooms seating more than 50 occupants where an evaluation indicates that sound reinforcement is needed. In such cases, a "speech transmission index" (STI) of 0.60 (or, alternatively a "common intelligibility scale," CIS, rating of 0.77) must be obtained. In addition, sound reinforcement must create at least a 70 dBA sound level which is maintained within 3 dB (at the 2000 Hz octave band*) at all points in the space.

    Note that dBA refers to an "A-weighted" decibel system, where the subjective experience of sound by humans enters into the calibration. Specifically, low-frequency decibel values are reduced.

    This LEED credit also requires that spaces using so-called masking systems cannot exceed 48dBA along with a few other requirements related to the masking of speech. Such systems can be used where speech privacy is desired between adjacent spaces, but where the unmediated sound transmission between those spaces would not provide adequate sound attenuation.

* Wondering what note corresponds to 2000 Hz? From this UNSW website: "500 Hz corresponds (roughly) to the musical note B4, or the B above middle C, as shown on the piano keyboard. 1000 and 2000 Hz to B5 and B6. On a piano or similar keyboard, if you go up 12 keys (160 mm to the right), you double the frequency. (Exactly double on most electronic keyboards and organs, slightly more than double on pianos.)" So 2000 Hz is B6, 2 octaves higher than the "B" just above middle C, as shown below.

piano keyboard with B6 shown