Indoor environmental quality and healthy buildings

People in North America spend roughly 90 % of their time indoors, so the indoor environment has a large effect on health, comfort and productivity. Indoor environmental quality (IEQ) covers the air people breathe, the thermal conditions they feel, the light they see by and the sound they hear. Much of IEQ is fixed by design, but construction practices decide whether the design is delivered: contaminated ductwork, wet materials sealed into walls, high-emitting products substituted for specified ones, poorly balanced ventilation and gaps in acoustic separations are all construction failures. This lesson covers each part of IEQ from a builder's point of view, with ventilation design standards as pointers rather than full design methods.

Ventilation and indoor air

Ventilation supplies outdoor air to dilute pollutants generated indoors, from people (carbon dioxide, moisture, odors, pathogens), materials (volatile organic compounds), cooking and combustion. The main US standards are ASHRAE Standard 62.1 for commercial and institutional buildings and the common areas of multifamily buildings, and ASHRAE 62.2 for dwelling units; the International Mechanical Code and state codes adopt or adapt them, and ASHRAE 170 covers health care facilities.

ASHRAE 62.1's ventilation rate procedure calculates the outdoor air needed in each zone from two parts: a rate per person, for pollutants from people, and a rate per unit floor area, for pollutants from materials and furnishings. The breathing-zone rate is then adjusted by a zone air distribution effectiveness that reflects how well supply air reaches occupants.

Here \(R_p\) is the outdoor air rate per person, \(P_z\) the number of people, \(R_a\) the rate per unit area and \(A_z\) the floor area. Carbon dioxide is a useful indicator of whether ventilation keeps up with occupancy. At steady state, the indoor concentration exceeds the outdoor concentration by the CO2 generation rate divided by the outdoor air rate per person; at about 15 cfm per person, a common design target for offices and classrooms, indoor CO2 settles about 700 ppm above outdoor levels.

# Steady-state indoor CO2 and outdoor air for the Cedar Row retail unit (illustrative)
c_out = 420          # ppm outdoor CO2
g = 0.011            # cfm of CO2 exhaled per sedentary adult (about 0.0052 L/s)
for q in (5, 10, 15, 20, 30):                  # outdoor air per person, cfm
    print(f"{q:3d} cfm per person -> about {c_out + g / q * 1e6:5.0f} ppm")
# ASHRAE 62.1 ventilation rate procedure, retail sales floor
area, density = 6460, 15 / 1000                # ft2, people per ft2 (default 15 per 1,000 ft2)
rp, ra, ez = 7.5, 0.12, 0.8                    # cfm per person, cfm per ft2, zone effectiveness
pz = area * density
vbz = rp * pz + ra * area
print(f"People {pz:.0f}; breathing-zone outdoor air {vbz:,.0f} cfm; zone outdoor air {vbz / ez:,.0f} cfm")

  5 cfm per person -> about  2620 ppm
 10 cfm per person -> about  1520 ppm
 15 cfm per person -> about  1153 ppm
 20 cfm per person -> about   970 ppm
 30 cfm per person -> about   787 ppm
People 97; breathing-zone outdoor air 1,502 cfm; zone outdoor air 1,877 cfm

Cedar Row's 6,460 square foot retail unit needs about 1,880 cfm of outdoor air at its default occupancy. More ventilation improves air quality but costs energy to heat, cool and move, which is why heat recovery (Lesson 5) and demand-controlled ventilation, which varies outdoor air with measured CO2 or occupancy, are so useful. For the 96 homes, ASHRAE 62.2 continuous ventilation through in-unit HRVs supplies fresh air to bedrooms and living areas and exhausts kitchens and bathrooms.

Builders influence ventilation performance directly. Ducts must be sealed, sized and routed as designed; fans must be installed with correct controls; outdoor air intakes must be kept away from exhausts, loading docks and parking garage openings; and every system must be tested, adjusted and balanced so that each room gets its design airflow. Commissioning verifies that ventilation rates are delivered in practice, not just on drawings.

Pollutant sources and low-emitting materials

Volatile organic compounds (VOCs) are carbon-based chemicals that evaporate at room temperature from paints, adhesives, sealants, flooring, composite wood and furnishings. Some, such as formaldehyde, are known or suspected carcinogens, and many cause irritation and headaches. Emissions are highest when products are new, which is why the period around occupancy matters. Other important indoor pollutants include fine particulate matter (from outdoor air, cooking, construction dust and wildfire smoke), radon, nitrogen dioxide and carbon monoxide from combustion, and mold.

Low-emitting product programs set limits on emissions or VOC content. Content limits cap the grams of VOC per liter of product, as in EPA's national architectural coatings rule and the stricter South Coast Air Quality Management District rules, which many specifications cite. Emissions testing measures what a product actually releases into a test chamber over time; the California Department of Public Health Standard Method (CDPH v1.2) is the most common test method in North America and underlies certifications such as GREENGUARD Gold and FloorScore. Rating systems such as LEED and WELL award credit for using compliant products, and builders must collect the documentation for every product in the relevant categories.

Substitutions are the main risk. A paint, adhesive or sealant that a subcontractor picks up from a supplier on short notice may not meet the specification, and one non-compliant product can cost a credit. Requiring product data before products arrive on site, checking containers on delivery and briefing trades on why it matters all help.

Radon

Radon is a colorless, odorless radioactive gas produced by the decay of uranium in soil and rock, and it is the leading cause of lung cancer among nonsmokers in the United States. It enters buildings through foundation cracks and openings, driven by pressure differences. EPA's action level is 4 picocuries per liter (about 150 becquerels per cubic meter), and EPA recommends testing all homes below the third floor. The International Residential Code's Appendix AF describes radon-resistant construction, which some states and localities require, especially in EPA radon Zone 1 counties. For larger buildings, a below-slab venting layer, sealed slab penetrations and a pipe to the roof make later mitigation simple and inexpensive.

Construction indoor air quality management

Construction itself can contaminate a building for years. Dust and debris in ductwork, mold growth in wet materials, and VOCs absorbed by insulation and carpet all harm the air quality occupants will breathe. A construction indoor air quality management plan, often based on the SMACNA IAQ Guidelines for Occupied Buildings Under Construction, addresses five areas: protecting HVAC equipment and ducts, controlling pollutant sources, interrupting pathways between dirty and clean areas, housekeeping, and scheduling.

Before occupancy, many projects either flush out the building with large volumes of outdoor air while maintaining comfortable conditions, or test indoor air for formaldehyde, total VOCs, particulates and other contaminants against set limits. Flush-out takes time and energy and may not be practical in winter; testing is quicker but risks failure and retesting. Moisture management is part of air quality too: wood framing, mass timber and drywall should be dry before they are enclosed, typically below 19 % moisture content for wood, to prevent mold.

Thermal comfort

Thermal comfort depends on six factors: air temperature, mean radiant temperature (the temperature of surrounding surfaces), air speed, humidity, clothing and activity level. ASHRAE Standard 55 and ISO 7730 use the predicted mean vote (PMV), a scale from −3 (cold) to +3 (hot), to estimate how a large group of people would rate their comfort, and the predicted percentage dissatisfied (PPD), which follows from PMV.

# Predicted percentage dissatisfied (PPD) from predicted mean vote (PMV), ISO 7730 / ASHRAE 55
import math
def ppd(pmv):
    return 100 - 95 * math.exp(-0.03353 * pmv ** 4 - 0.2179 * pmv ** 2)
for pmv in (-2, -1, -0.5, 0, 0.5, 1, 2):
    print(f"PMV {pmv:+4.1f}: PPD {ppd(pmv):4.1f} %")

PMV -2.0: PPD 76.8 %
PMV -1.0: PPD 26.1 %
PMV -0.5: PPD 10.2 %
PMV +0.0: PPD  5.0 %
PMV +0.5: PPD 10.2 %
PMV +1.0: PPD 26.1 %
PMV +2.0: PPD 76.8 %

Even in ideal conditions, about 5 % of people are dissatisfied, because individuals differ. ASHRAE 55 generally aims for a PMV between −0.5 and +0.5, which corresponds to a PPD of about 10 % or less. Envelope quality matters to comfort as well as energy: cold window surfaces and drafts from air leaks lower the radiant temperature and create discomfort near the perimeter, which better windows and airtightness solve.

Overheating is a growing concern in multifamily buildings, especially in units with large windows and no cooling, and heat waves such as the 2021 Pacific Northwest heat dome caused deaths mostly among people in homes without air conditioning. Some jurisdictions now require cooling in rental housing or set maximum indoor temperatures, and others are considering similar rules. Heat pumps provide cooling as well as heating, which is one reason they suit Cedar Row; shading, moderate window areas and operable windows reduce cooling loads. Lesson 11 returns to heat resilience.

Daylight, views and lighting

Daylight and views of the outdoors are linked with occupant satisfaction and wellbeing, and good daylighting reduces electric lighting. Common metrics include spatial daylight autonomy (the share of floor area that receives enough daylight for most of the year) and annual sunlight exposure (the share that receives too much direct sun, causing glare and overheating). The trade-off with energy is real: Lesson 5 showed that more glazing increases heat loss, so designers use window placement, high-performance glazing, light shelves and shading rather than simply more glass. Electric lighting should provide appropriate light levels with good color rendering and controls that respond to daylight and occupancy.

Acoustics

Noise from neighbors, building services and outdoor traffic is one of the most common complaints in multifamily buildings. Sound transmission class (STC) rates how well an assembly blocks airborne sound, and impact insulation class (IIC) rates floors against footfall and impact noise. The International Building Code requires walls and floors between dwelling units to achieve STC 50 (or 45 if field tested) and floors to achieve IIC 50 (or 45 if field tested). Acoustic performance is easily lost in construction: unsealed gaps at the edges of walls, back-to-back electrical boxes, rigid connections across resilient channels and flanking paths through floors and ceilings can reduce a wall's field performance dramatically. Mass timber floors, as in Cedar Row's Option B, usually need a topping, underlayment or ceiling to meet impact requirements.