Preventing indoor overheating and building community heat resilience

Human caused climate change is leading to more extreme heat events, also known as heatwaves in Canada and elsewhere. Extreme heat events increase the risk of indoor overheating, which refers to the excessive build-up of heat inside buildings without adequate climate control through passive and mechanical cooling. For occupants, this can lead to discomfort, lost productivity, exacerbation of health conditions, heat injury, hospitalization, and even death. While everyone is at risk from extreme heat, those most susceptible to indoor overheating include seniors, people who are socially isolated or who live alone, people with disabilities and certain chronic conditions, pregnant women, infants, and young children. Most buildings have been constructed based on past climatic conditions and are not suitable for current extreme heat events and hotter future climates. While high outdoor temperatures are the primary cause of indoor overheating, the design, operation, and maintenance of buildings can exacerbate overheating risk through a variety of mechanisms, including:   

• Lack of overall building shade, unshaded window exteriors and large window areas. These building features and orientation allow for higher solar heat gains, especially on the south, east and west walls, and through skylights.
• High insulation levels and airtight building envelopes. Buildings with these features reduce heat gains from the outdoor environment but also slow the transfer of trapped indoor heat to the outdoors. If the indoor space is not well-ventilated, the trapped heat can increase the risk of overheating.
• Floor and room location. The top floors of multi-unit residential buildings tend to have higher indoor temperatures than lower floors, especially if the roof or attic are not insulated or cool roof material (heat reflective) is not used.
• Poor natural ventilation. Lack of good cross ventilation by prevailing breezes, especially at night, reduces the potential for cooling through open windows.

There are effective design and retrofit strategies to reduce indoor overheating risk. Mechanic cooling with an air conditioner (AC) or heat pump is a highly effective strategy to reduce heat-related mortality and morbidity, but not a perfect solution. Many at-risk households cannot afford to install, operate, or repair cooing systems. Mechanical cooling also contributes to greenhouse gas emissions, contributes heat to the outdoor environment, and strains power supplies during extreme heat events. In addition, reliance on mechanical cooling can lead to severe health impacts during  power outages. Therefore, passive approaches should be prioritized in the design or retrofit of buildings. Combining passive and mechanical strategies can ensure thermal safety and comfort in the changing climate.

Community and neighbourhood characteristics can influence both outdoor heat exposure and indoor overheating risk. Urban heat islands, limited tree canopy, and a lack of green space can increase temperatures during extreme heat events. Equity-informed approaches for urban greening, shade, cool roofs, and climate-responsive land-use planning are needed to reduce heat exposure and build community resilience.

The resources listed below are intended to help environmental public health professionals improve their understanding of infrastructural and behavioural risk factors that contribute to indoor overheating in Canada. This guide includes resources related to building design, retrofit, codes, and standards to reduce indoor overheating and policy considerations to protect against indoor overheating. It also includes resources on nature-based and built environment strategies for building community heat resilience.

For more information please see our Extreme heat risk, preparedness, and response subject guide here.

Understanding infrastructural and behavioural risk factors that contribute to indoor overheating

• Elevated indoor temperatures and health (Public Health Ontario, 2026)
  This evidence review summarizes the health risks of elevated indoor temperatures and factors that influence indoor heat exposure. It presents practical strategies to reduce heat-related harms, particularly for susceptible populations.

• Guidance on upper indoor temperature limits: Protecting the health of older adults (Health Canada, 2026)
  This guidance reviews current evidence on indoor heat exposure and health risks among older adults, including factors that contribute to indoor overheating and a recommendation for an indoor temperature limit of 26°C to reduce adverse health effects, particularly for older adults.

• Indoor overheating: A review of vulnerabilities, causes, and strategies to prevent adverse human health outcomes during extreme heat events (Kenny et al., 2024)
  This review examines the physiological, behavioural, building, and neighbourhood-level factors that contribute to indoor overheating and heat-related health risks. It provides an overview of susceptible populations, exposure pathways, and ways to reduce overheating in homes and other indoor environments.

Building design, retrofit, codes, and standards to reduce indoor overheating

• Cooler condos – Understanding and reducing overheating risks (Zero Emissions Innovation Centre 2026)
  This guide explains the causes and risks of indoor overheating experienced by condominium communities and provides practical approaches to improve comfort, safety, and resilience during extreme heat events. It lays out building and resident factors that increase susceptibility and explores solutions like heat pumps, shading, improved ventilation, and emergency preparedness measures.

• BC Building Code 2024: Protection from overheating in dwelling units (Government of BC, 2024)
  This bulletin introduces new BC Building Code requirements to help prevent overheating in new homes, including a requirement for at least one living space in each dwelling unit to maintain a temperature of 26°C or less under summer design conditions.

• Keeping our cool: Preventing overheated buildings in the climate crisis (NCCEH, 2023)
  This webinar provides an overview of indoor overheating in Canada in the face of climate change. It covers design guidelines and standards to limit overheating in buildings, alongside examples of how to achieve “climate ready” buildings cost effectively in new and existing buildings.

• Space cooling strategies (BC Housing, 2022)
  This one-pager outlines no-cost or low-cost cooling strategies for residential buildings, as well as the pros and cons of various mechanical cooling strategies such as portable air conditions, personal fans, mini heat pumps and central air conditioning.

• Irreversible extreme heat: Protecting Canadians and communities from a lethal future (Intact Centre on Climate Adaptation, 2022)
  This guide presents a series of actions individuals, property owners and managers, and communities can take to mitigate the risks of indoor overheating. Actions are divided into three categories: 1) planning and behavioural changes, 2) working with nature, and 3) improving buildings and public infrastructure.

• Climate resilience buildings: guideline for management of overheating risk in residential buildings (National Research Council Canada, 2022)
  This report provides a general framework to evaluate overheating risk in buildings (chapters 6-9), identifies potential mitigation strategies to reduce overheating risk (chapter 10), and presents the application of the framework to three types of buildings: detached homes, attached homes, and multi-unit residential buildings (chapters 11-13).

• Resilient cooling strategies – A critical review and qualitative assessment (Zhang et al., 2021)
  This article provides a critical overview of traditional and novel building cooling strategies and how they hold up under heat waves and power outages. The authors suggest that a combination of cooling strategies with different functions is important to achieving thermal resilience.

• How to retrofit buildings in a climate emergency: Stepwise EnerPHit(The Passive House Network, 2021)
  This webinar provides an overview of Stepwise EnerPHit, a tool to help building owners understand climate risks to buildings and plan retrofits that are adapted and resilient to a changing climate.

Policy considerations to protect against indoor overheating  

• The right to cool. Protecting renters from extreme heat: A municipal response (Climate Caucus, 2026)
  This toolkit outlines municipal policy options to protect renters from extreme heat, including tenant protections, cooling standards, and housing resilience measures.

• Thermal safety in existing multi-unit residential buildings (Metro Vancouver, 2026)
  This policy toolkit outlines strategies for improving thermal safety in existing multi-unit residential buildings across BC's Lower Mainland, including measures to reduce indoor overheating, enhance occupant health and comfort, and support climate resilience through building retrofits, policy changes, and public education.

• Too hot to think small: The case for a right to cool in British Columbia (UBC Centre for Climate Justice, 2025)
  This report makes the case for a "Right to Cool" in British Columbia, by exploring the limitations of current cooling measures and proposes equitable policy approaches that address the social, housing, and health factors that shape vulnerability to extreme heat.

• Climate resilient buildings for urban Indigenous housing and service providers (Aboriginal Housing Management Association, 2024)
  This report explores approaches to strengthening climate resilience in urban Indigenous housing, with a focus on asset management, emergency preparedness, community engagement, and long-term planning. It also provides recommendations for housing providers and policymakers to support safer, more resilient indoor environments in a changing climate.

• Heat-proofing community housing: Prioritizing extreme heat adaptation for vulnerable Canadians (Action Canada, 2023)
  This report explores how policymakers can better protect community housing residents in urban areas, including establishing a maximum indoor temperature and modernizing Canada’s building codes to ensure community housing is climate resilient.

• Policy tools to create and support cooler, safer indoor living spaces (Vancouver Coastal Health, 2023)
  This report summarizes the results from a review of policy and regulatory options that could increase thermal safety in homes. While this was developed with the Vancouver Coastal Health region in mind, there is broad applicability of these policy and regulatory options to other regions across Canada.

Nature-based and built environment strategies for heat resilience

• Thermal effects of cool roofs and urban vegetation during extreme heat events in three Canadian regions (Lu et al., 2023)
  This peer reviewed article examines how urban greening and cool roofs can reduce temperatures during extreme heat events in the Ottawa-Montréal, Calgary, and Vancouver regions.

• Nature based solutions to mitigate urban heat island effects in Canadian cities: Literature review (Hayes et al., 2022)
  This literature review examines the effectiveness of nature-based solutions, such as urban forests and green infrastructure, for reducing urban heat island effects and building heat-resilient communities.

• Irreversible extreme heat: protecting Canadians and communities from a lethal future (Intact Centre on Climate Adaptation, 2022)
  This guide outlines a series of actions individuals, property owners and managers, and communities can take to mitigate the risks of extreme heat events. It includes sections on working with nature to protect Canadians from extreme heat.

• Urban heat islands tools and resources (Health Canada, 2022)
  This webpage compiles tools, guidance documents, case studies, and planning resources community planning, urban greening, and public health approaches to reducing heat exposure.

• HealthyPlan.City (HealthyDesign.City, 2021)
  This mapping tool is designed to help planners, public health professionals and policy makers understand inequities across urban neighbourhoods by intersecting built environment variables (e.g., tree canopy cover or land surface temperature) with the percentage of susceptible populations who live there.  
   
• Urban heat island mitigation strategies: 2021 update (Institut national de santé publique du Québec, 2021)
  This literature review provides an overview of measures to mitigate urban heat islands for decision-makers, public and private property managers, municipal stakeholders, non-profit organizations, and other project designers can adopt to ensure healthier and more comfortable living environments.

• Reducing urban heat islands to protect health in Canada (Health Canada, 2020)
  This report provides tips, strategies, and case studies to help public health professionals support local governments and organizations to reduce urban heat islands in Canada, with advice focused on outdoor air temperatures.