Indoor Air Quality and Ventilation in Newly Built Homes

In Summary

• Reducing heat loss in residential buildings is a necessary part of Ireland’s Climate Action Plan: Informed residential retrofitting and design of new builds is key.
• Current regulations and energy rating tools overlook real-world indoor environmental performance. Building standards and Building Energy Rating (BER) assessments lack measured indoor air quality (IAQ) data, limiting their ability to ensure healthy, comfortable homes.
• Energy efficiency improvements can compromise indoor air quality without appropriate ventilation strategies. Natural ventilation, by its nature, is highly variable and is also influenced by the behaviour of residents, often resulting in year-round unhealthy IAQ, with higher concentration of pollutants in winter and overheating in summer.
• This policy brief draws from research conducted as part of the ALIVE Project in the University of Galway and University College Dublin to make recommendations for these integrated actions to relevant policymakers. The ALIVE project assessed how well natural ventilation can reduce energy use and prevent overheating in energy-efficient buildings, while still maintaining acceptable IAQ.
• The EPBD recast (May 2024), to be transposed by May 2026, requires EU Member States to set requirements for adequate Indoor Environmental Quality (IEQ) in both new and existing residential buildings, and to include IEQ-related recommendations in Energy Performance Certificates.

Glossary

1. Ventilation and Health: Issue Overview

Ireland’s strategy to reduce building-related carbon emissions has focused heavily on improving the energy performance of its housing stock through large-scale retrofitting and more stringent standards for new construction. These efforts are essential to meeting Irish national and EU climate targets. Key measures include increasing the thermal insulation of dwellings and improving airtightness, i.e., limiting the amount of uncontrolled air leakage through the building envelope. While these design changes reduce heating demand due to lower heat loss, they also limit the natural movement of air through the building. While this improves energy efficiency, these energy-efficiency measures introduce critical risks to indoor environmental quality (IEQ), specifically Indoor Air Quality (IAQ) and thermal comfort. The problem arises from a performance gap: buildings meet regulatory requirements on paper (e.g. air permeability thresholds, passive ventilation provisions), but often fail to provide adequate ventilation, effectively remove indoor pollutants, or mitigate overheating under real-world conditions.

In many homes, particularly those without mechanical ventilation systems, natural ventilation, which relies on passive openings like wall and trickle vents, often proves insufficient in delivering adequate indoor air quality, making it an increasingly concerning issue. In theory, these openings should provide sufficient airflow to maintain safe indoor environmental conditions. In practice, however, airtight homes relying solely on passive airflow are not achieving the recommended air exchange rates (AERs), particularly during colder and warmer seasons when window and vent use is controlled by occupants. This has led to a measurable decline in IAQ in numerous newly built homes studied in this project across Ireland.

Despite advances in energy-efficient building design, naturally ventilated (NV), energy efficient dwellings are experiencing a performance gap between intended energy saving and real-world indoor air quality (IAQ). Specifically, low air exchange rates (AER), especially in winter, can result in poor dilution of indoor pollutants such as PM2.5, CO₂ and TVOCs. The current passive ventilation systems (wall vents and trickle vents) are insufficient to maintain adequate IAQ year-round, especially during winter when occupants reduce window use due to cold outdoor temperatures. This is compounded by increased pollutant exposure during common activities like cooking and limited occupant knowledge of ventilation best practices, ultimately undermining the intended benefits of airtight, energy-efficient homes. The Irish building regulations, as outlined in Technical Guidance Document F (Ventilation), specify that required ventilation rates in dwellings should primarily be met through a combination of background ventilators and natural infiltration. While features like windows are designed for intermittent ‘purge’ ventilation to quickly clear pollutants, the home’s primary ventilation is meant to be provided by background ventilators (wall and trickle vents) designed for constant airflow.

Poor IAQ, particularly in energy-efficient homes that rely solely on natural ventilation, poses health risks with wide-reaching consequences. Elevated levels of PM2.5, CO₂ and TVOCs have been linked to a range of adverse health outcomes. PM2.5, which was found to exceed World Health Organization (WHO) 24-hour limits on 93% of winter days in monitored Irish kitchens, is associated with respiratory conditions such as asthma and chronic obstructive pulmonary disease (COPD), as well as increased risk of cardiovascular events including strokes and heart attacks. High indoor CO₂ levels exceeding 1000 ppm for a longer period can impair cognitive function, including concentration, memory, next-day performance, and decision-making. TVOCs, often emitted from cleaning agents, personal care products and building materials, contribute to symptoms such as headaches, dizziness and skin or eye irritation, and can lead to long-term respiratory issues with repeated exposure. Vulnerable groups such as the elderly, young children and individuals with pre-existing health conditions are disproportionately affected, particularly in winter months when cold temperatures discourage window opening and limit ventilation. Economically, the health costs of indoor air pollution in Ireland is estimated at €0.15bn, or 0.06 percent of GDP per year. Poor indoor climate can lead to increased healthcare costs. With its impact on asthma and respiratory conditions, poor IAQ can cost European health services over €2.6 billion per year. These findings reinforce the urgent need for integrated policy solutions that address the intersection of energy performance, indoor air quality and public health.

2. ALIVE Project Research Findings

The findings of the ALIVE project highlight the challenges associated with the delivery of adequate ventilation by passive systems, and identifies the combined impact of occupant behaviour and ventilation system design issues. The ALIVE project used sensors to collect data in buildings and created computer models to understand the impact of natural ventilation on health and energy efficiency. The ALIVE project and its associated studies [1][2][3] provide robust empirical, longitudinal and simulation-based insights into these issues:

Indoor Air Quality (IAQ) Deficiencies in naturally ventilated energy efficient homes

• CO₂ exceeded 1000 ppm during 94% of winter sleeping hours in nine dwellings breaching WHO and EN16798 recommendations and thresholds.
• Fine particulate matter (PM2.5) concentrations exceeded the WHO 24-hour guideline in 92% of kitchen measurements during winter and 51% in summer (n=9) even with the monitored homes using electric cooking, suggesting that gas cooking could further exacerbate the problem.
• TVOCs frequently exceeded 430 ppb, particularly in bedrooms, and were linked to the use of personal care and cleaning products. Peak values reached 1200–4600 ppb which can lead to health impacts.
• Ventilation rates (AERs) were consistently below recommended levels with mean values of winter mean: 0.21 hr^-1; summer mean: 0.33 hr^-1; annual mean: 0.28 hr^-1).

Thermal Performance and Overheating

• During summer, seven out of nine monitored rooms failed CIBSE TM59 Criterion A for overheating. Temperatures exceeded 24°C for an average of 54% of time across bedrooms and average of 44% in kitchens during summer[4].
• Adaptive comfort models indicated that natural ventilation alone was often insufficient to fulfil the potential of passive cooling and maintain indoor temperatures within recommended IEQ categories, even during shoulder seasons (spring and autumn).

Occupancy-Ventilation Interaction

• Occupant behaviour, including reduced winter window use, variable cooking habits and limited purge ventilation (manual opening of windows), exacerbated seasonal indoor air quality (IAQ) issues. This interaction is not accounted for in current Dwelling Energy Assessment Procedure (DEAP) or Building Energy Rating (BER) assessments. A newly created optimisation framework demonstrated that occupancy, window operation duration and heating setpoints critically affect heating consumption, CO₂ levels and discomfort hours².

3. Policy Recommendations

The general findings of the ALIVE project indicate that while airtightness improves energy performance, natural ventilation alone is insufficient to maintain healthy indoor conditions year-round, without significant occupant engagement; examples of excellent practice exist within the dataset. To address this, the following interventions are proposed:

1. Develop a Framework for Post-Occupancy Performance Verification: To close the gap between design and real-world performance, building regulations should evolve to include post-occupancy performance. As a first step, we recommend piloting a program for seasonal IAQ and overheating testing in a representative sample of new homes. This data would inform the development of a cost-effective verification method, such as sensor audits or validated CO₂ decay tests, that could be integrated into future regulations.
2. Introduce Risk-Based Auditing of Indoor Environmental Quality: Rather than mandating universal testing, regulations should require developers to demonstrate compliance through risk-based auditing. A statistically significant percentage of homes from new developments would undergo seasonal post-occupancy testing for IAQ and overheating. If a development’s sample fails to meet performance standards (e.g., CIBSE TM59 or EN 16798-1), it would trigger wider testing and require remedial action, thus incentivizing developers to build for real-world performance from the outset.
3. Promote Hybrid or Mechanical Ventilation Integration: Challenges have been observed in the underperformance of passive natural ventilation in new homes, underscoring the need for careful consideration during the design phase. Where natural ventilation is likely to be insufficient to achieve desired indoor conditions, hybrid or mechanical ventilation strategies should be explored. Kitchen extraction systems should not only comply with the minimum airflow rate requirements (e.g., ≥30 L/s as outlined in the TGD Part F), but also be subject to routine performance checks over time to ensure ongoing pollutant removal efficiency during cooking, highlighted in the ALIVE study as a key source of indoor air pollution. These interventions would ensure that ventilation is not left to occupant discretion and reduce IAQ degradation.
4. Educate Occupants and professionals on energy and health: Occupant behaviour plays a decisive role in the performance of naturally ventilated homes. National awareness campaigns should be launched to educate residents on the effective use of trickle vents, purge ventilation and recognition of poor air quality indicators such as condensation, odours, or headaches. Simultaneously, industry professionals (including BER assessors, retrofit contractors and ventilation system installers) should receive updated training that includes ventilation commissioning, sensor-based verification and best-practice IAQ strategies. Integrating these modules into professional development pathways ensures a competent workforce that understands both energy and health outcomes.
5. Integrate IEQ into Energy Rating and Retrofit Assessment Tools: To ensure occupant health and comfort are not side-lined in the pursuit of energy efficiency, the national DEAP and NEAP frameworks should be expanded beyond static inputs to explicitly include indoor environmental quality (IEQ) performance indicators. While ventilation type and heating system efficiency are considered, these frameworks do not currently assess time-based or occupant-facing outcomes such as air quality or overheating risk. Metrics such as the number of hours CO₂ exceeds 1000 ppm, the percentage of occupied hours above 26°C, and ventilation performance (e.g., air exchange rates or purge capability) would provide a more complete picture of real-world performance. Linking SEAI grant eligibility to these combined energy and IEQ indicators would incentivise more holistic design decisions that balance energy use, indoor air quality, and thermal comfort. This is particularly important as retrofit activity scales up, with a risk of unintended consequences like poor ventilation or overheating in highly airtight homes. Pilot programmes using in-situ monitoring (CO₂, PM2.5, temperature, humidity) in A-rated homes can help verify the alignment between predicted and actual indoor conditions. These data can create a feedback loop to refine performance-based thresholds, support improved DEAP/NEAP methodologies, and inform future iterations of building regulations that prioritise occupant well-being alongside decarbonisation targets.

4. Policy Implementation

These policy recommendations will require a coordinated implementation approach across a range of sectoral stakeholders:

Conclusion

Ireland’s climate action ambitions require improvements to the energy related performance of Ireland’s building stock. Recommended measures include retrofitting of poorly rated dwellings and the design and construction of new builds to reduce heat losses over time. However, such improvements should not come at the cost of occupant health and indoor environmental quality. The findings of the ALIVE project underscore an important gap between regulatory compliance and real-world performance, particularly in energy efficient homes relying on natural ventilation. To bridge this gap, policy must evolve beyond energy consumption metrics to embrace a more holistic framework that integrates measured indoor air quality, occupant behaviour and seasonal performance. This requires updating building regulations, embedding ventilation standards in retrofit grant schemes, educating both residents and industry professionals and expanding BER assessments to reflect real-world indoor conditions.

By implementing the recommendations outlined in this paper, which are grounded in empirical evidence and aligned with best international practice, policymakers can ensure that Ireland’s building stock is not only energy efficient but also healthy, and comfortable for residents. The latest recast of the Energy Performance of Buildings Directive (EPBD), published on 8 May 2024 and entering into force on 28 May 2024, formally introduces Indoor Environmental Quality (IEQ) at the European level and embeds it across the building life cycle. Member States, including Ireland, are required to transpose the directive into national law by 29 May 2026. This means that optimal IEQ must be integrated into energy performance requirements for new buildings and major renovations, key IEQ parameters such as temperature, humidity, carbon dioxide, and particulate matter must be monitored through smart building systems, and energy performance certificates must reflect IEQ. This integrated, evidence-based approach is essential not only for delivering robust climate action, but also for protecting the planet and improving the quality of indoor environments where people live and work.

References

1. Alhindawi, I., McGrath, J. A., Sood, D., O’Donnell, J., & Byrne, M. A. (2025). A seasonal assessment of indoor air quality and thermal performance in naturally ventilated airtight energy-efficient dwellings. Building and Environment, 276, 112862. https://doi.org/10.1016/j.buildenv.2025.112862
2. Sood, D., Alhindawi, I., Ali, U., Finn, D., McGrath, J. A., Byrne, M. A., & O’Donnell, J. (2025). Machine learning based multi-objective optimisation of energy consumption, thermal comfort and CO2 concentration in energy-efficient naturally ventilated residential dwellings. Building and Environment, 267, 112255. https://doi.org/10.1016/j.buildenv.2024.112255
3. Sood, D. Evaluating the effects of occupancy on energy use and indoor environmental quality in residential building archetypes over spatial and temporal scales. PhD thesis, University College Dublin. School of Mechanical and Materials Engineering and UCD Energy Institute, 2025. https://researchrepository.ucd.ie/entities/publication/0f826f11-3b15-4c2c-b4f7-edf66ce53c8a
4. Alhindawi, I., Fernandes, J.M., McGrath, J.A., Sood, D., O’Donnell, J. and Byrne, M.A., 2025. Temporal Assessment of Overheating Risk and Thermal Environment in Naturally Ventilated Energy-Efficient Airtight Dwellings. Journal of Building Engineering, p.114027. https://doi.org/10.1016/j.jobe.2025.114027

Acknowledgement

This publication has emanated from research supported partly by a grant from the Sustainable Energy Authority of Ireland (SEAI) under the ALIVE Project: Assessing Indoor Environmental Quality and Energy Efficiency In a Range of Naturally-Ventilated Buildings: A Multi-Disciplinary Approach. The Government of Ireland funds the ALIVE project (19/RDD/537) through the SEAI Research, Development and Demonstration Funding Programme 2019. The opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the SEAI. I would also like to thank Simon Jones from Air Matters for his feedback. Preparation of this policy paper has been facilitated by the NexSys Strategic Partnership Programme. NexSys is funded by Research Ireland Grant no. 21/SPP/3756 (NexSys Strategic Partnership Programme). Observations and recommendations in this paper do not necessarily reflect the views of NexSys affiliated research organisations or industry partners.

^[a] While SR 54 outlines the need for ventilation assessment during retrofit design, this recommendation calls for measurable validation through on-site testing (e.g., flow rate testing, IAQ checks) both before and after works are completed.