Surprising, easy-to-fix issues can cause your home to overheat regularly, especially in small-scale multi-unit homes (SSMUH).
Below are innovative strategies and smart design principles to prevent overheating and improve occupant comfort when designing multifamily buildings. Gain valuable insights into managing heat effectively and ensure your building remains cool and livable for all residents.
The increasing frequency of heatwaves has made overheating a major concern for all building types everywhere - even in mild climates such as Vancouver has. This issue is particularly important in multifamily buildings, which have unique characteristics that worsen overheating and impact more residents.
Important Problems, Simple Solutions
As the building owner, you should care about resident comfort and productivity because the health and safety of more people are at risk. Comfortable living conditions support the well-being of all residents, whether extended family or rental tenants. If you're a landlord, providing a healthy environment for all residents not only boosts tenant satisfaction and reduces turnover but also is your legal responsibility. Climate-resilient design is no longer an option for the passionate few but a survivability issue for everyone.
Some of the causes of overheating are far more evident or significant with multiplexes, but the solutions apply both to multifamily buildings and to houses.
Inadequate Insulation
While we generally think of insulation in the walls and roof as a way to help keep a home's interior warm by holding the heat indoors, we forget that the reverse is true during the summer. Better insulation in the building helps hold back the heat during very hot weather. Better insulation can be achieved by thicker walls (more insulation between the studs or trusses), but this approach is less effective. Instead, a layer of insulation that runs continuous past the studs on either the outside or the interior side to prevent the heat from traveling through the structure to the indoors; this is what is referred to as reducing "thermal bridging". Some insulation is available with a foil face that will reflect most radiant heat.
High Occupant Density
Although most cities will allow a multiplex / SSMUH to be larger than a single-family home, the number of residents per square foot of floor area is greater. For example, a family of four living in 2200 ft² give off a certain amount of body heat and heat from other activities. In contrast, four families of between two and four could be living in a 4000 ft² multifamily home. That's close to twice as many people in the same amount of space - twice as much heat from human activities.
The solution to this is a more efficient ventilation and cooling system. Instead of building twice as much inefficient ventilation equipment, design and build a more efficient system to lower both the construction cost and the operating cost and to provide a more comfortable indoor environment.
More Windows
Solar gain is a common cause of uncomfortable indoor temperatures in both single-family and multifamily homes. Multifamily buildings also have less flexibility in window placement due to different unit orientations, and they typically have proportionately more windows than single-family houses, further complicating heat mitigation.
Most windows allow too much infrared sunlight to enter, trapping heat inside. Blinds and curtains are often ineffective because radiant heat still passes through the glass and becomes trapped indoors. Overhangs and other shading devices can limit unwanted sunlight, but they are often impractical or cost-prohibitive in multifamily buildings.
Choosing very high-performance triple-glazed windows, preferably Passive House Certified units, allows large windows that let in plenty of light yet block much of the infrared heat, effectively addressing overheating.
Poor Ventilation
Perhaps more problematic than inefficient ventilation systems is poor ventilation design. A typical single-family house relies on the exhaust fans from your dryer, bathroom, and range hood by design and on various gaps and cracks in the construction of your roof and walls in actuality. In a multiplex, one or two outer walls of a dwelling unit and often the ceiling will be shared with an adjacent unit and therefore not exposed to the fresh outdoor air. Trying to pull stale, warm air out through only two or three walls instead of four walls and a roof results in more "dead air spaces".
Instead, use a closed-loop system using a heat recovery ventilator (HRV or ERV) - again preferably a Passive House certified model. This system will distribute fresh air to your living room and bedrooms 24 hours a day all year long. It captures heat from outgoing air in the winter, and it pulls heat out of incoming air during the summer. I explain this concept in more detail in my article How Passive Cooling Keeps Your House Cool During Heatwaves.
Inefficient Water Heaters
Many homes and businesses still use hot water equipment that relies on burning natural gas. The pilot light generates a small amount of constant heat, while the burner flame produces significant heat, some of which radiates into the home. Additionally, the combustion flue that exhausts to the outdoors releases heat along its entire length. Insulating the flue can help, but a better solution is to choose electric water heaters.
Electric heating elements are nearly 100% efficient, transferring virtually all their heat to the water.
Furthermore, pipes carrying hot water from the storage tank to sinks, showers, bathtubs, and washing machines can contribute to indoor heat. Consider how long you typically run the water before it gets hot; all the cool and tepid water you waste was once hot water sitting in the pipes, giving off its heat to the indoor space. To minimize this, design the home to reduce piping distances, and heavily insulate the pipes so they and the water inside stay hot longer, releasing heat at a much slower rate.
Inefficient Lighting
Although many homes are no longer lit with 100W incandescent bulbs in desk lamps and 300W halogen bulbs in floor lamps, there is still a range of light fixtures with varying degrees of inefficiency. A decade or two ago, compact fluorescent bulbs in a rental suite could be replaced with traditional incandescent bulb. Today, many new condo units are still designed with halogen spotlights in the kitchen and bathroom because they produce high quality light in spite of running quite hot and giving off considerable heat.
Selecting light fixtures that use high-quality LED elements address both the need for high quality lighting and the need to limit the amount of heat that a cooling system needs to overcome. Try to select fixtures that are still easy enough to replace, however.
Limited Exterior Surface Area
Even during heatwaves, the outdoor temperature will drop enough at night that "flushing" the home interior with outdoor air will bring the indoor temperature down. For a single-family home, the surface area of the roof and walls allows the accumulated heat to radiate away during the night also.
An optimized, efficiently-designed multiplex will generally have a simpler overall geometric form. This means that the ratio of the exterior surface area to the interior volume is lower; we call this an efficient "form factor".
While the best solution is to minimize heat gain during the day as much as possible, provide as many operable windows as possible. A large portion or the entire window should open; a small operable pane in the corner is ineffective. Ensure that the windows are fitted with insect screens to allow residents to keep the windows open throughout the night without fear of blackflies and mosquitoes ruining a good night's sleep.
Air Leakage
When it's hot outside, it's important not only to cool the air indoors but to ensure that hot air is not leaking into the home - or that air-conditioned air isn't leaking out. If you left your refrigerator door wide open, the refrigeration system obviously wouldn't be able to overcome the heat loss. When there are many gaps around doors, windows, pipes, ducts or wiring that run from inside to outside or there are gaps at building joints, an air-conditioning system's performance will be degraded and not able to overcome the heat gain. In a multifamily building, there are likely to be more penetrations and openings than in a single-family house. The solution to this leakage is the same as one of the keys to retaining heat in winter: improve airtightness of the walls and roof by sealing all the cracks, joints, and penetrations.
Dark Colours
Dark-coloured building materials absorb more solar energy and get hotter.
The temperature of any roof is much higher than other surfaces on the building, so the choice in roofing material makes a big difference in how much heat the building gains from the sun. Light-coloured ("low albedo") options are available - especially for flat roof materials.
Since window frames conduct more heat to the interior per square inch, dark window frames - which are gaining popularity - that consequently get hotter are the worst offenders. The solution here if a white frame is undesirable is "over-insulating" the frame. That means extending exterior wall insulation on front of the frame to shield it from the sun in the summer and hold in more heat in the winter. This approach is common in Passive House and other Net Zero projects.
For the last half of my career as an architect, my focus has been on regenerative, ultra high-performance architecture including Net Zero and Passive House principles. Compiling practical, proven strategies from a variety of high-performance projects enables me to craft an optimized design solution that doesn't break the bank.
You could own a rental property that commands higher rents and gets next to no complaints, or you could have to respond to pleas from tenants dying in the heat despite the various AC hoses hanging out the windows.
My SAPPHR Strategy isn't a "nice to have" add-on; it is integral to my design process. Many designers and architects draw first and ask questions later. I turn the usual sequence on its head and research first instead of wasting time on ideas that aren't workable or don't satisfy the client's objectives. Ultra high-performance is not optional in my professional opinion; it is my moral duty. The key to both my Ultrahome and Invisible Multiplex solutions is the comprehensive research, design, and documentation process in the SAPPHR Strategy. Click on the link below to download the SAPPHR guide.
If you plan to build an ultra high-performance multiplex or house in the next year, you can use the button below to book a free, 30-minute call with me and learn the first steps to take to avoid wasted time and money.
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 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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