December 14, 2023

Comparing CO₂ Standards Across Green Building Certification Systems

Green Buildings

There's a lot of talk about outdoor CO2 pollution and its role in climate change, with carbon dioxide being the primary human-made greenhouse gas. However, CO2 concerns aren't limited to just the outdoor environment. The COVID-19 pandemic shed light on the importance of indoor air quality. It's no longer just about making buildings more energy-efficient; it's also about ensuring healthy indoor environments for people.

Indoor CO2 pollution primarily originates from human respiration. Inadequate ventilation can result in sick building syndrome (SBS) symptoms such as headaches, fatigue, nausea, and irritability. However, detecting elevated CO2 levels within our indoor spaces can be challenging. Consequently, assessing and addressing CO2 pollution in enclosed environments becomes very important.

Indoor air quality monitors provide valuable data on particulate matter (PM), carbon dioxide (CO2), and total volatile organic compounds (TVOC) levels. However, it's crucial to compare readings with optimal levels. This is where indoor air quality standards play a role, setting a benchmark for evaluating and tracking a building's air quality over time.

This article presents a comprehensive overview of the acceptable CO2 thresholds defined by the leading Green Building certification systems (WELL, LEED, RESET, and Fitwel), pivotal information for assessing building air quality.

Source: “Harvard Business Review”

Introducing Green Building Certification Systems

Green building certification provides guidelines for constructing and operating sustainable buildings. There are two types of certifications: those promoting overall sustainability and those focusing on human health and wellbeing. Some standards focus on one or the other, while others do both. A standard will have a sustainability focus if it considers environmental performance, while it will have a health focus if it considers the health performance of buildings.

WELL, LEED, and RESET systems focus on both sustainability and health, while Fitwell focuses mainly on health and well-being.

Ensuring indoor air quality is a critical component of green building certification standards, which helps maintain occupant comfort and promotes health and environmental safety. Among the most crucial aspects of indoor air quality in green building certification systems is monitoring and regulating CO2 levels. 

Different green building certification systems have adopted varying standards for measuring and regulating CO2 levels. Organizations such as WELL, LEED, RESET, and Fitwel have specific criteria and measurement techniques. 

Several factors must be considered when selecting a relevant certification standard, including complying with local regulations, selecting appropriate standards for the building's purpose, and evaluating certification options. For example, compliance with standards such as ASHRAE Standard 62.1 in the US or country-specific indoor air quality norms is critical.

Source: ASHRAE Technical FAQ


The levels of Carbon Dioxide (CO2) are mainly addressed in three features of the Air Concept: A01 (Fundamental Air Quality), A03 (Ventilation Design), A06 (Enhanced Ventilation), and A08 (Air Quality Monitoring and Awareness). According to the feature A06, CO2 levels in the breathing zone of all regularly occupied spaces should be kept below 900 ppm to earn one point. Two points can be earned by reducing CO2 levels to 750 ppm. Table 1 shows guidelines on monitoring density in occupiable spaces required by WELL.

Table 1. Number of Monitors Required in Occupiable Spaces Based on Project Area

Source: WELL Performance Verification Guidebook

For accurate measurement of CO2 levels, WELL recommends continuous monitoring using annually calibrated sensors placed strategically across the building. 

LEED (Leadership in Energy and Environmental Design)

The beta version of LEED v5 O+M, announced at Greenbuild 2023, introduces new standards for indoor air quality (IAQ) monitoring. The focus is on real-time, continuous IAQ monitoring to improve occupant comfort and well-being while identifying energy-saving opportunities. 

The new IEQ Credit: Indoor Air Quality Performance offers up to 13 points. 

  • Three points can be earned by maintaining CO2 levels below 1000 ppm (Minimum IAQ limit). 
  • Four points can be earned by reducing CO2 levels to 800 ppm (Enhanced IAQ limit).

Learn how Atmocube can help earn up to 10 points.


RESET (Real-time Environmental Sensing and Evaluation Technology)

The RESET Standard is modular, allowing project teams to implement specific modules based on their priorities. Certification only requires completing some modules. RESET Air, a data standard for air quality monitoring designed to prioritize ongoing results and long-term occupant health, is one of these modules.

RESET Air requires constant measurement of five parameters: PM2.5, TVOC, CO2, temperature, and relative humidity. The RESET certification highlights the importance of continuous air quality monitoring, which identifies changes due to occupancy, behavior, and seasons. 

  • Commercial interiors can achieve acceptable or high-performance levels, with CO2 thresholds under 1000 ppm for acceptable and 600 ppm for high performance
  • For Core & Shell projects the thresholds are 800 ppm or 350 ppm over outdoor levels. 

RESET emphasizes continuous air quality monitoring of indoor air pollutants, especially for CO2, using certified sensors such as Atmocube, a RESET Grade B -accredited monitor. This ensures indoor air quality and allows swift corrective actions.


Fitwel v2.1 introduces pathways to accumulate certification points, explicitly targeting indoor air quality (IAQ) enhancement – except for commercial sites. These strategies encompass the establishment of a comprehensive IAQ policy (6.3), the implementation of air quality assessments (6.4), and the transparent communication of results to building occupants (6.5). Essential to this framework is an IAQ policy that aligns with Fitwel's exacting criteria, possesses universal applicability, and establishes integration within leases and manuals.

Compliance with IAQ testing procedures (6.4) is imperative to earn certification points. This entails post-construction or renovation IAQ testing, coupled with continuous monitoring efforts that ensure the maintenance of specific air quality benchmarks such as PM2.5 and CO2 levels. To earn points, CO2 monitoring results should demonstrate values below 1100 ppm or 700 ppm over the ambient concentration. 

Regular CO2 level measurement can be accomplished through intermittent assessments utilizing handheld sensors or seamless integration of continuous monitoring.

Table 2. Comparing CO2 Thresholds Between Different Green Building Certifications

WELL v.2   |   LEED v.5   |   RESET   |   Fitwel

Measuring CO2 for Green Building Standards  

How do you measure CO2 in your indoor space? Do you pay for inspection services annually? 

Installing a real-time air quality monitor in your space is an effective way to continuously monitor indoor air quality. 

Atmocube, a RESET Grade B accredited air quality sensor, is an excellent solution for your needs, providing accurate and precise readings every time. In addition to CO2 readings, the sensor monitors other pollutants important for Green Building certification points (See Table 3).  

Table 3. Atmocube Sensor Specifications

Post tags
Interested in monitoring indoor air quality and environmental comfort of your space?
Let's chat
Atmocube on the wall