Will Your House or Multiplex Be Livable During The Next Heatwave?

Thousands of people are dying in their own homes. Will you?

I'm going to show you design considerations for making a new house or multiplex safe and comfortable for the whole family - or families - during intensifying heatwaves.

Today's Heatwaves

How Bad Is It?

Heatwaves have been growing hotter and more frequent starting in the 70s and accelerating for the past several years, and more people are dying in their homes during these periods as a result. Strategies that people have been using to keep their homes cool are beginning to fail. People remember hot weather in their youth and assume they will handle it as they did before, despite the facts that a) the temperatures are higher now, and b) they are older and less able to regulate body temperature. People also assume that air conditioning will be adequate to protect them, but eventually it won't.

A sea captain once told me that our weather patterns operate on a roughly 7-year cycle. Major heatwaves since 1976 operated on that cycle until around 2022. Europe suffered prolonged and severe heatwaves in 2003, 2010, 2022, 2023, and Europe is again hit this year (2026) with 40°C+ in France (link), Germany (link), Spain (link).

The heatwaves were responsible for 70 000 excess deaths (2003), 56 000 excess deaths (2010), 62 000 excess deaths (2022), 48 000 excess deaths (2023), and so far this year 10 000 excess deaths. Prior to this, 1911, 1947, 1976, and 1994 were similarly intense for Europe. Note three things though: 1) the decreasing intervals between severe heatwaves, 2) the increase in urbanization that results in fewer people living near the shade and temperature mitigation of forests, and 3) those older records are being broken.

2010, 2019, and 2026 are the result of a specific atmospheric pattern, an Omega Block, but all of the heatwaves were the result of persistent high pressure areas. The oceans have been absorbing massive quantities of heat (link), heating up more than ever recorded before (link), and they will be giving it back (link to Super El Niño).

This isn't just a Europe problem. The hottest parts of India are accustomed to ~40°C in the pre-monsoon season, but now they're facing 45°C weather (link). The eastern USA was hit with a heat dome at the beginning of July, and the prairies will see another one in the coming week (link). There's an anomalously warm body of water estimated to be centred in the central and eastern equatorial Pacific Ocean, about 50-150m below the surface and headed toward South America.

All these news articles about extra-hot weather isn't a matter of discomfort or memes; it points to a real, growing peril. Last summer, I was on vacation in a hot country. The hotel pool was nearly empty, and here's why. Usually, a pool is an enjoyable reprieve during hot weather even in the sun. However, the sun was able to heat up the water to perhaps ~30°C. The air was around 33°C, so there was no reprieve and the experience was very uncomfortable. I could feel my brain frying and headed back inside. Without reprieve in sufficiently hot conditions, the body internal temperature can cause damage and death.

You're Not A Spectator

You will need air conditioning in your home, and an AC system you buy or build now based on current climate data in the building code will not be enough in the future. Everyone agrees on that point. At some time in the near future, most people's homes AC systems will be almost useless as I explain in my other article, "How To Design Or Renovate Your House For Comfort During Heatwaves (link)". This is more significant a topic now that many people work from home at least part-time. Do you?

Taking a couple days off when it's too hot, or hanging out in your garage - if you have one - might have worked before, but how feasible is not working for several days or more in a row once or more every summer?

Air Conditioning Won't Fix Your Problem

The BC Building Code and Vancouver Building By-Law currently require at least one room in each dwelling unit to be capable of being maintained at a maximum of 26°C. This means active air conditioning, but that cooling equipment is being designed based on historical climate data.

Have you ever looked at the AC equipment for a reasonably well-off family's recently built house in the Middle East? Compared to the size of the house, the AC units are huge.

The population in the Middle East have learned to manage and avoid the high temperatures of midday in the summer. North American and European cultures are not similarly set up.

I go into this topic much more in my article, "Don't Install Air Conditioning In Your House - You're Wasting Your Money" (link). Suffice it to say that simply adding AC to your house or multiplex without adjusting the design is not a sustainable solution. However, here are some keys to a solution that are sustainable.

How Do We Survive This?

Reduce Cooling Equipment Using Passive Design

We Canadians understand that the better way to keep a home warm is to add insulation to the walls and roof; since the 40s the response to colder weather hasn't been adding a car-sized industrial gas-fired boiler in the kitchen just to keep us warm. However, that IS largely the defective thinking at play when addressing hot weather.

Air conditioning can help during a heatwave currently, but it should not be the primary design strategy. It should be the final layer in a home that has already reduced its cooling demand.

This matters for comfort, construction cost, and electrical capacity. If a multiplex - or even a single-family house - is designed with too much unshaded glass, poor airtightness, weak insulation, and inefficient internal systems, the cooling equipment has to be larger (and noisier and expensive) to compensate. In some projects, the higher electrical demand causes costly service upgrades. Even with suitably sized equipment, the temperature will not be uniform; it can feel terribly hot near the window or at head height.

Heat pumps are more efficient, but traditional AC systems are really just crude, inefficient one-direction heat pumps. If you want to understand how heat pumps work, I have a primer in my article, "How Does A Heat Pump System Work? (Simplified Explanation) (link)"

A better approach is first to reduce the cooling needed. EXTERIOR shading blocks heat before it reaches the glass. Once the heat gets in, it doesn't really leave. Continuous insulation slows heat passing through the roof and walls. Airtight construction prevents hot outdoor air from leaking in and cooled air from leaking out. High-performance windows reduce unwanted heat from the sun while still admitting useful daylight. A compact, well-organized building shape is easier to insulate, easier to air-seal, and less complicated (less expensive) to build.

Then and only then, the HVAC system can be smaller and more targeted. A right-sized heat pump can provide cooling without becoming the main architectural idea. The owner does not need to pay for a large system simply because the design ignored the sun.

This is the practical side of high performance. It is not about adding conspicuous equipment until the home can overcome the climate. It is about using intelligent design to reduce the need for equipment in the first place.

The strongest version of my Invisible Multiplex approach is therefore not invisible to view but invisible to the budget. The form, shading, glazing, insulation, and systems all work together so the owner is not forced to solve predictable design problems with larger machinery and a larger electrical bill.

More Insulation To Keep The Heat Out

Most people still think of insulation as something that keeps a home warm in winter. That's only half of the story. Insulation slows down heat movement - regardless of whether that's toward the exterior or toward the interior.

During a heatwave, insulation also slows the movement of heat into the home. This matters because overheating is caused not only by hot air outside. The siding, roofing, and window frames are heated by the sun, and that heat steadily moves into the home throughout the day. Anyone with a South-facing garage has felt the oven blast when they opened the interior door. Once that heat is inside the building, the cooling system has to deal with it.

Just as in cold weather, continuous insulation prevents the studs in the wall from transferring heat more readily to the cooler side. This transfer is called thermal bridging, and it undermines the performance of the wall or roof. A mostly uninterrupted layer of insulation reduces that bridging. We cannot add insulation blindly though; the assembly must be designed carefully to manage moisture, airtightness, constructability, and cost to create a much more stable indoor environment instead of just a more expensive shell.

Reduce Internal Heat Gains

Heat comes not only from punishing weather. A single-family home generally does not have this concern, but in a multigenerational or multifamily home, a surprising amount of heat is generated inside. There are more people and more daily activity within a compact building. More people means more body heat. More kitchens mean more cooking. More laundry, more appliances, more lighting, more showers, and more plug loads (laptops and other devices) all add heat that the cooling system needs to remove.

In my other article, "How Passive Cooling Keeps Your House Cool During Heatwaves (link)", you can see this in some simple diagrams.

These activities all create heat, which we call "internal heat gains". In a compact multiplex, these gains can become a major part of the overheating problem. In a study of a multifamily building without adequate cooling monitored during a 2-3-day heatwave a few years ago, suites took only one day to climb to inhospitable temperatures but then took five days to cool down to an acceptable temperature. We call that "thermal inertia".

This is one reason why mechanical and plumbing coordination must be part of a building's design. Plumbing fixtures, piping, and ventilation systems should not be scattered based solely on preference. Their locations affect construction cost, energy use, comfort, and maintenance.

Shorter hot water runs are a good example. When a bathroom is far from the water heater, hot water sits in the pipes after each use and releases heat into the home. The next person then runs the tap while waiting for hot water. Clustering bathrooms, kitchens, laundry, and mechanical spaces reduces these losses and simplifies construction.

Lighting should also be part of the heat strategy. Good daylighting reduces the amount of artificial light needed during the day. In a full multigenerational home or multiplex even the heat from LED light fixtures adds up.

Establish A Safe Zone

The most thermally stable space in a home is the most comfortable, but the most stable is not necessarily the most enjoyable. In old, inefficient homes, a fully underground basement is the warmest in extreme winters and the coolest in the summer. However, it's the darkest and most depressing space year-round. In Metro Vancouver, full basements are uncommon anyways.

A multigenerational home should not begin with the question of how many suites can fit on the lot. It should begin with the question of who most needs the home to function well when conditions outside become difficult. The building code now requires at least one room to be able to be limited to 26°C, so think carefully about where you want everybody congregating during an extreme heat event.

During a heatwave, the most vulnerable person in the home may be an aging parent who is less able to regulate body temperature, but it might instead be a young child who cannot easily recognize heat stress, an infant whose body is still learning to regulate heat, or a family member with reduced mobility who cannot simply move to a cooler part of the house. A resilient multigenerational home should plan for that spectrum of realities from the start.

The most stable suite in the home should be the one that is easiest to access and easiest to keep comfortable. Often, this will be a ground-oriented suite with a direct entrance, fewer stairs, and a close relationship to a shaded outdoor area. It should not feel like the leftover space in a basement. It should feel like a dignified home within the larger home.

This is where overheating resilience becomes more than a technical subject. It becomes part of the family’s long-term plan. A suite that remains comfortable in August, bright in February, and accessible in twenty years is not an add-on. It is one of the strongest arguments for building a purpose-designed multigenerational home in the first place and a unique sellable feature secondarily.

Bring Light Deep Into The Home

Ground floor and basements suites often fail because they are treated as spaces to be made legal rather than as spaces to be made joyful.

Good daylighting is not the same thing as bigger windows. A bright lower-level suite does not require a wall of glass. In fact, too much glass creates glare, heat gain, privacy loss, and a weaker building envelope. Good daylighting is the careful design of where light enters, how far it travels, and how it feels when it reaches the people inside.

Tall windows are usually more useful than wide windows because the height of the window head determines how deeply daylight can enter the room. Glass near the floor often contributes less useful light, while it still adds cost and reduces insulation value. A better strategy is to place the glass where it will work hardest.

Courtyards, light wells, clerestories, flared window openings, and light-coloured interior surfaces can all help move daylight deeper into the plan. These strategies are especially useful in a high-performance wall assembly, where thicker walls can otherwise make windows feel tunnel-like. Instead of treating that thickness as a problem, the design can use it. A flared opening can bounce light inward and make the wall feel substantial rather than heavy.

Exterior shading must be designed in conjunction with the openings - not tacked on. The objective is soft, useful light without excessive solar heat gain. That requires attention to orientation, window proportions, glass performance, privacy, and shade. Done properly, a lower suite does not feel secondary. It feels calm, bright, and intentional. That is especially important in a multigenerational home, where the suite may become a parent’s long-term home rather than a temporary rental compromise.

I go into daylighting techniques in more detail in my article, "Daylighting Design for a Happier Space (link)"

Intentional, Functional Outdoor Space

Remember above where I mention not having trees in abundance nearby? The outdoor space around a multigenerational home should not be treated as decoration. It can be one of the home’s most useful climate-control features and is almost always used strategically in Passive House projects.

A shaded courtyard, a covered patio, a deep balcony, or a planted side yard can become an outdoor room that supports the way extended families actually live. It can be the place where grandparents sit comfortably while children play nearby. It can be the place for family meals, quiet morning coffee, or a break from indoor activity when the house is full. In a dense multiplex, this shared outdoor space can provide relief without requiring each household to retreat behind a closed door.

The climate value is just as important. Hard paving, exposed walls, and unshaded windows can turn the area around a building into a heat trap. Planting, shade structures, roof overhangs, exterior screens, and carefully placed walls can make the same area cooler and more usable. The goal is not simply to create a pleasant view but to shape the microclimate around the home. A cool outdoor room is not a luxury feature. It is a low-energy living space, a family gathering place, and a buffer between the heat of the city and the comfort of the home.

This is also where the Invisible Multiplex and Ultrahome can show their purpose through deep shade, strong edges, protected entries, and outdoor spaces that are shaped in response to sun and heat. Like older architectural traditions in hot climates, the form can tell you what problem it is solving. Since architecture is problem-solving manifest, performance becomes part of the architecture rather than an expensive correction applied after the fact.

The Invisible Multiplex™ (link) and Ultrahome™ (link) are my design recipes geared specifically toward ultra comfort in the face of extreme weather due to climate change. They go beyond Net Zero and Passive House but while optimizing for constructability to avoid huge cost premiums.

You could continue to enjoy your home even during the really bad heatwaves. Your home will be bright, pleasantly warm, and supplied with fresh air constantly. Alternatively, you could sit in a darkened bedroom with the portable AC running full blast or in the garage working on your laptop trying to ignore the smell of automotive fluids.

If you want a free, 30-minute consultation with me to discuss how to design a home to be heatwave-resistant without spending a bucketload of extra money, click the button below to book a time that works for you.

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DISCLAIMER:

The information included in this article is to an extent generic and intended for educational and informational purposes only; it does not constitute legal or professional advice. Thorough efforts are made to ensure the accuracy of the article, but having read this article, you understand and agree that Daniel Clarke Architect Inc. disclaims any legal liability for actions that may arise from reliance on the information provided in this article. I am an architect in BC, but readers are recommended to consult with their own architect on their specific situations before making any decisions or exercising judgement base on information in the article.

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