Photo: Chip Allen Photography
Innovations in technology, manufacturing, and automation enable architects to meet the new expectations of homebuyers in the multifamily market.
Innovations in the multifamily sector of building design and construction include a generation of proven fenestration systems serving novel envelope systems and facade designs that combine energy efficiency and long-term performance with the market-pleasing trend toward more indoor-outdoor experiences. This course closely looks at performance-boosting building approaches developed and put into practice recently with an emphasis on fenestration techniques that focus on thermally broken aluminum windows, doors, and sliding and multi-slide openings.
BUILDING FOR MULTIFAMILY USE – A CHANGING LANDSCAPE
Multifamily building has gone through several significant changes in the past few years. As more occupants turn to work-from-home options, the demands of individual living spaces have moved from larger communal areas to more personal spaces. Expectations for increased comfort, healthy living spaces, clean air, access to natural light, and operable windows have also increased as occupants are spending more time indoors. Building technology has advanced and some become automated, creating more consistent, resilient, and repeatable delivery of building components. Windows, doors, and wall systems can now be manufactured with efficient streamlined production, delivery, and installation.
Leading the long list of new innovations in multifamily construction is building performance, which has progressed significantly in terms of innovation, especially in the design and construction of the shell or building envelope. Improved fenestration options, glazing, rain screen technology, thermal breaks, and water management strategies now can work in harmony to create multifamily homes that are durable, healthy, energy-efficient, and aesthetically creative.
Photo courtesy of All Weather Architectural Aluminum
Low-rise multifamily projects are increasingly focused on affordability for occupants, which includes reducing energy costs through performance improvements.
A BOOST IN PERFORMANCE
Of all the latest advancements in low-rise multifamily construction, the design and integration of performance-improving building components is strikingly significant. With an increased awareness of electrical generation and the link to mitigating climate change in terms of carbon emissions, reducing the amount of energy used to heat, cool, and light residential spaces is becoming a focal point across the board. However, it is important to remember that while promoting a cleaner and more sustainable environment outside the home is critical, for many homeowners and renters poorly insulated or shabbily designed homes have a much more immediate impact.
While some architects have the opportunity to consider and design high-end projects such as those catering to luxury townhome developers, most multifamily projects in the next 10 years will consist of low-rise buildings in an effort to address the current housing crisis. These buildings will likely be targeted at working-class families, and this makes sense considering the growth of affordable housing projects in the U.S., as well. Building performance directly impacts the health and well-being of occupants through poor indoor air quality, water intrusion, and overall comfort. A poorly designed and constructed home also carries the consequence of a monthly pain point of high energy costs for the homeowner.
According to recent figures from the National Association of Home Builders (NAHB), over 43 million Americans live in multifamily housing or approximately 31 percent of the total housing stock in the United States.1 Given increasing urbanization, inflation, financial challenges for first-time home buyers, and high interest rates cooling the single-family home market, this number is expected to rise over the next few years. Most occupants are renters and a disproportionate number are poor, minority, single parents with children.
When looking at the existing housing stock, a study by the American Council for an Energy-Efficient Economy (ACEEE) found that improvements in energy efficiency could reduce multifamily building energy use by around 15-30%, especially through targeted interventions such as upgrading HVAC systems, improving insulation, and enhancing window performance. This level of reduction in energy use is significant, especially for low-income multifamily, non-white, and Hispanic households who disproportionally experience high energy burdens, and use a large share of their income to pay for energy bills. Nearly half of low-income multifamily households experience an energy burden greater than 6% as compared to 2% for non-low-income households. Research by ACEEE uncovered that electric end uses, for example, space heaters or mobile air conditioning units, are proving to be the leading cause of high energy consumption for low-income, non-white, and Hispanic multifamily households.
For new multifamily construction and retrofit projects, a focus on building performance can impact both occupants and building owners. NAHB has also noted that today’s potential homeowners are environmentally aware and have an increased interest in homes that promote sustainable design through carbon reduction and overall lowered energy use. The return on investment for upgrading the performance of buildings through improved materials and design can be relatively rapid as these units often can be offered at a premium to an eager market.
Photo by Brian Gassel; courtesy of Niles Bolton Associates
The natural properties of aluminum allow the metal to be used in a variety of high-performance and aesthetically interesting fenestration options.
High Expectations for Fenestration
Fenestration has proven to be a critical element in modern multifamily construction with many expectations for performance, operability, and aesthetics. Balancing the design and performance goals of a project can be a challenge but also rewarding. Modern low-rise, or buildings under five stories tall, increasingly seem to require the best of all worlds: expansive views, natural light, interesting exteriors, and energy efficiency─all on a conservative construction budget.
For the architect, the specification of the material type of frames can have a significant impact on the project in terms of both cost and performance.
Today’s choices for fenestration include aluminum, vinyl, wood, fiberglass, and composite material. Of these, aluminum, vinyl, and wood capture most of the market share. The pros and cons of each material type need to be weighed against the overall goals of the project, budget, and how well each type integrates with the building envelope.
Aluminum frames are widely used in fenestration for multifamily housing due to their durability, lightweight material, and strength. One of the primary advantages of aluminum is its ability to support larger glass panes while maintaining a slim profile that allows for improved line-of-sight and maximized natural light. Aluminum is resistant to corrosion, can be extruded into custom shapes and lengths, can be painted or anodized to match any color, and is very low maintenance. However, aluminum has high thermal conductivity, meaning it easily transfers heat and cold, making it less energy-efficient compared to other materials. To address this, aluminum frames often include thermal breaks—plastic sections within the frame that help reduce the flow of heat.
Photo: Chip Allen Photography
Innovations in technology, manufacturing, and automation enable architects to meet the new expectations of homebuyers in the multifamily market.
Innovations in the multifamily sector of building design and construction include a generation of proven fenestration systems serving novel envelope systems and facade designs that combine energy efficiency and long-term performance with the market-pleasing trend toward more indoor-outdoor experiences. This course closely looks at performance-boosting building approaches developed and put into practice recently with an emphasis on fenestration techniques that focus on thermally broken aluminum windows, doors, and sliding and multi-slide openings.
BUILDING FOR MULTIFAMILY USE – A CHANGING LANDSCAPE
Multifamily building has gone through several significant changes in the past few years. As more occupants turn to work-from-home options, the demands of individual living spaces have moved from larger communal areas to more personal spaces. Expectations for increased comfort, healthy living spaces, clean air, access to natural light, and operable windows have also increased as occupants are spending more time indoors. Building technology has advanced and some become automated, creating more consistent, resilient, and repeatable delivery of building components. Windows, doors, and wall systems can now be manufactured with efficient streamlined production, delivery, and installation.
Leading the long list of new innovations in multifamily construction is building performance, which has progressed significantly in terms of innovation, especially in the design and construction of the shell or building envelope. Improved fenestration options, glazing, rain screen technology, thermal breaks, and water management strategies now can work in harmony to create multifamily homes that are durable, healthy, energy-efficient, and aesthetically creative.
Photo courtesy of All Weather Architectural Aluminum
Low-rise multifamily projects are increasingly focused on affordability for occupants, which includes reducing energy costs through performance improvements.
A BOOST IN PERFORMANCE
Of all the latest advancements in low-rise multifamily construction, the design and integration of performance-improving building components is strikingly significant. With an increased awareness of electrical generation and the link to mitigating climate change in terms of carbon emissions, reducing the amount of energy used to heat, cool, and light residential spaces is becoming a focal point across the board. However, it is important to remember that while promoting a cleaner and more sustainable environment outside the home is critical, for many homeowners and renters poorly insulated or shabbily designed homes have a much more immediate impact.
While some architects have the opportunity to consider and design high-end projects such as those catering to luxury townhome developers, most multifamily projects in the next 10 years will consist of low-rise buildings in an effort to address the current housing crisis. These buildings will likely be targeted at working-class families, and this makes sense considering the growth of affordable housing projects in the U.S., as well. Building performance directly impacts the health and well-being of occupants through poor indoor air quality, water intrusion, and overall comfort. A poorly designed and constructed home also carries the consequence of a monthly pain point of high energy costs for the homeowner.
According to recent figures from the National Association of Home Builders (NAHB), over 43 million Americans live in multifamily housing or approximately 31 percent of the total housing stock in the United States.1 Given increasing urbanization, inflation, financial challenges for first-time home buyers, and high interest rates cooling the single-family home market, this number is expected to rise over the next few years. Most occupants are renters and a disproportionate number are poor, minority, single parents with children.
When looking at the existing housing stock, a study by the American Council for an Energy-Efficient Economy (ACEEE) found that improvements in energy efficiency could reduce multifamily building energy use by around 15-30%, especially through targeted interventions such as upgrading HVAC systems, improving insulation, and enhancing window performance. This level of reduction in energy use is significant, especially for low-income multifamily, non-white, and Hispanic households who disproportionally experience high energy burdens, and use a large share of their income to pay for energy bills. Nearly half of low-income multifamily households experience an energy burden greater than 6% as compared to 2% for non-low-income households. Research by ACEEE uncovered that electric end uses, for example, space heaters or mobile air conditioning units, are proving to be the leading cause of high energy consumption for low-income, non-white, and Hispanic multifamily households.
For new multifamily construction and retrofit projects, a focus on building performance can impact both occupants and building owners. NAHB has also noted that today’s potential homeowners are environmentally aware and have an increased interest in homes that promote sustainable design through carbon reduction and overall lowered energy use. The return on investment for upgrading the performance of buildings through improved materials and design can be relatively rapid as these units often can be offered at a premium to an eager market.
Photo by Brian Gassel; courtesy of Niles Bolton Associates
The natural properties of aluminum allow the metal to be used in a variety of high-performance and aesthetically interesting fenestration options.
High Expectations for Fenestration
Fenestration has proven to be a critical element in modern multifamily construction with many expectations for performance, operability, and aesthetics. Balancing the design and performance goals of a project can be a challenge but also rewarding. Modern low-rise, or buildings under five stories tall, increasingly seem to require the best of all worlds: expansive views, natural light, interesting exteriors, and energy efficiency─all on a conservative construction budget.
For the architect, the specification of the material type of frames can have a significant impact on the project in terms of both cost and performance.
Today’s choices for fenestration include aluminum, vinyl, wood, fiberglass, and composite material. Of these, aluminum, vinyl, and wood capture most of the market share. The pros and cons of each material type need to be weighed against the overall goals of the project, budget, and how well each type integrates with the building envelope.
Aluminum frames are widely used in fenestration for multifamily housing due to their durability, lightweight material, and strength. One of the primary advantages of aluminum is its ability to support larger glass panes while maintaining a slim profile that allows for improved line-of-sight and maximized natural light. Aluminum is resistant to corrosion, can be extruded into custom shapes and lengths, can be painted or anodized to match any color, and is very low maintenance. However, aluminum has high thermal conductivity, meaning it easily transfers heat and cold, making it less energy-efficient compared to other materials. To address this, aluminum frames often include thermal breaks—plastic sections within the frame that help reduce the flow of heat.
Vinyl frames are extruded polyvinyl chloride (PVC) with colors embedded in the frames at the time of manufacturing. The properties of PVC are very successful at arresting heat transfer, making this an ideal choice for projects with energy efficiency goals. PVC is also resistant to moisture, rot, and insects. Yet detracting from vinyl is the fact that the material is not as durable as other types of material as it can warp or degrade over time, especially when exposed to extreme temperatures. While very cost-effective for smaller fenestration needs, vinyl can limit the design options for multifamily buildings as wider frames are required, compared to aluminum windows.
For a traditional design choice, wood frames offer a classic look and strong insulation properties for multifamily projects. Aesthetically wood frames clad in aluminum or vinyl on the exterior can offer exposed wood on the inside to enhance the look and feel of the interior of the home. Wood can be painted or stained and performs well for both energy efficiency and soundproofing. But wood frames do come with several drawbacks. Compared to aluminum and vinyl, upfront costs of wood are usually higher, and wood is susceptible to damage from moisture and insects, meaning regular maintenance is required. In addition, wood frames are thick, reducing the amount of light let into the home and diminishing the view.
Photo courtesy of Aluminum Extruders Council
The pour and debridge process creates a channel filled with polyurethane to halt the flow of heat energy from the glass to the aluminum frame.
As California Goes, So Goes the Nation
California has long been a bellwether state for providing a glimpse of how the nation will move forward from a legislative standpoint, especially related to environmental concerns such as pollution, air and water quality, and energy efficiency. For multifamily building, this may mean a shift in priorities that require a more sustainable design approach.
Achieving green building certifications or satisfying model energy code goals for sustainability is an attractive option for many multifamily projects whether to genuinely protect the environment or as a marketing strategy. However, in California, sustainable design for low-rise multifamily projects is not an option. Title 24 is part of the California Code of Regulations2, specifically focused on energy standards that govern the design and construction of buildings to improve energy efficiency and reduce environmental impact. Implemented by the California Energy Commission (CEC), Title 24 is updated every three years with the most recent version released in 2022.
Title 24 sets higher standards for energy efficiency than the International Energy Conservation Code (IECC), which serves as a model energy code for many states. One of the most distinctive features of Title 24 is its Net Zero Energy (NZE) initiative. Under recent updates, all new residential buildings, including low-rise multifamily projects, are required to achieve NZE or near-NZE performance. This means that new homes must produce as much energy as they consume, typically by integrating renewable energy systems, such as solar photovoltaics (PV). While this may not be practical for all projects nationwide, the emphasis on energy use reduction and lowering carbon emissions both embodied and occupied are becoming more relevant.
For the building envelope, particularly in terms of insulation and window performance Title 24 limits the total amount of window or glass area relative to the building’s exterior wall area. For multifamily buildings, the general rule is that the fenestration area should not exceed 40% of the gross exterior wall area. This is to ensure that while windows are used for daylighting, they do not contribute excessively to energy inefficiency.
In terms of design, these requirements allow for some flexibility for the architect. The glass-to-wall ratio is not just about the percentage of glass but also about the performance of the glass itself by designating specific U-Factor and Solar Heat Gain Coefficient (SHGC) ratings based on climate zone. If a project has a higher glass-to-wall ratio, it can still meet Title 24 requirements when high-performance glazing is used to reduce energy loss. Likewise, if the frames and wall systems (basically all components of the building envelope) work in harmony, the building can achieve these aggressive performance goals.
This is where aluminum-framed windows can help achieve project goals by allowing designers to incorporate more glass into projects. This in turn allows more light through doors and windows while also delivering on performance expectations.
Un-Bridging the Window
Aluminum by nature is a naturally conductive material. Heat energy will readily pass through aluminum. To compensate for this, manufacturers of extruded aluminum products have developed different technologies to arrest the heat flow and basically “un-bridge” the thermal bridging.
The first approach to breaking the thermal bridge in aluminum window and door frames is called pour and debridge. The process begins with the extrusion of aluminum profiles for the window frame. A channel is then created along the thermal bridge – the area of the frame where heat could transfer between the inside and outside. In the pour step, a high-performance insulating material, typically polyurethane, is poured into the channel and allowed to cure and harden. Next, the metal along the bottom of the channel, under the polyurethane, is cut away to fully separate the inner and outer aluminum sections, creating a thermal break.
The pour and debridge process follows guidelines published by the American Architectural Manufacturers Association in the AAMA QAG-1-09 specification, or Quality Assurance Processing Guide for Pour and Debridged Polyurethane Thermal Barriers. The guide outlines best practices for processing, handling, and testing polyurethane thermal barriers used to improve the energy efficiency of aluminum frames by reducing thermal conductivity.
Pour and debridge fenestration systems can offer impressive performance, protecting against temperatures as far as -100°C (-148°F). Neither extreme cold nor hot temperatures will transfer through an aluminum frame with a pour and debridge thermal barrier, and the capacity of the frame to structurally support large pieces of glass is not diminished.
The second innovative technology for breaking thermal bridges in aluminum frames is using a polyamide thermal strut. Polyamide is a type of synthetic polymer commonly known as nylon. It is widely used in industrial applications due to its strength, durability, and thermal resistance. For thermal struts, a specific type of polyamide known as PA66 (Nylon 66) is often used, sometimes reinforced with glass fibers to further improve its structural integrity. Polyamide, like polyurethane, is non-conductive, meaning it acts as an insulator, which is key in preventing the transfer of heat or cold between the inside and outside of the aluminum frame.
For this process, two separate aluminum profiles, one for the interior and one for the exterior – are joined together by polyamide thermal struts. The struts are manufactured to exacting specifications separately, and then inserted between the aluminum profiles into grooves created during extrusion. As with the pour and debridged technology, a guide has been produced by AAMA on the specifications named AAMA QAG-2-12 Voluntary Quality Assurance Processing Guide for Polyamide Thermal Barriers.
Besides providing for an effective thermal break in the window, the polyamide strut technology allows for different color profiles or tones on the frame – one choice of color on the inside and another on the outside, for example.
Photo courtesy of All Weather Architectural Aluminum
Polyamide thermal struts are another technology used in fenestration frames to create a thermal break.
IGUs
Choosing the appropriate framing material for fenestration and doors can go a long way in improving the performance of a building, but innovations in glazing technology and design are also contributing to performance goals. As design trends in multifamily projects move toward increasing window sizes to improve views and invite more daylight into the living space, the performance of the window unit becomes more critical. Of note, the specification of Insulating Glass Units (IGUs) has changed the performance landscape – and expectations – for low-rise multifamily projects, both improving thermal performance and reducing noise within the home.
IGUs consist of two or more panes of glass separated by a gas-filled space. The gas, usually argon, is a better insulator than air and reduces heat transfer between panes. Spacers between the panes help center and support the glass. Historically spacers were made from aluminum, however, the glass to aluminum connection point served as a thermal bridge. Today, a new spacer technology called a “warm-edge spacer” has been developed to help arrest this heat flow. Made from less conductive materials like stainless steel, silicone, and neoprene or foam, warm-edge spacers improve the energy efficiency of the window while also helping secure the panes in place. The glass panes are carefully sealed around the edges to prevent moisture intrusion and gas leakage.
The insulation and air sealing allow the interior surface of the glass to remain warmer, relatively the same as the indoor ambient temperature. By keeping the interior glass surface warmer, IGUs reduce the likelihood of condensation forming on windows, which can lead to mold growth or damage to interior finishes over time.
Low-emissivity (Low-E) coatings are applied to one or more glass surfaces, further improving the unit’s thermal performance by reflecting infrared energy (heat) while allowing visible light to pass through. Coating types, colors, and characteristics can be “tuned” or customized by the architect to achieve specific goals. These goals may be site-specific and based on the physical orientation of the building. For instance, in cooler climate zones, south-facing windows may call for a specific higher SHGC rating to increase heat gain during the winter months. Visible Transmittance (VT) may also be adjusted with low-E coatings. VT measures the amount of visible light transmitted, impacting daylighting and occupant comfort. Higher VT values indicate better natural lighting within the building. Depending on the type of building and needs of occupants, specifying VT can provide a creative option to satisfy occupant requirements. When needed, lower VT ratings are better suited to reduce natural lighting to avoid glare, provide privacy, or create a specific aesthetic for the interior.
Multifamily homes often face noise challenges, particularly in urban environments or areas near transportation hubs. IGUs can be designed to offer improved sound insulation by varying the thickness of the glass panes or using laminated glass in conjunction with the IGU. This provides enhanced acoustic control, improving occupant comfort and privacy, which is particularly important in densely populated housing developments.
IGUs are commonly used in curtain wall systems for multifamily projects. These systems allow for large expanses of glass that maximize natural light while maintaining high energy efficiency. Curtain walls with IGUs can be used in a rainscreen configuration to provide additional moisture protection for the building envelope. The rainscreen design helps keep water out by using a ventilated air cavity behind the facade material, preventing moisture penetration into the insulation layer and offering another way to help reduce the risk of mold or structural damage.
Value Engineering as a Path to Success
For some projects, architects may decide to employ the concept of value engineering and introduce multiple material types for windows to balance energy performance, budget, and aesthetic expectations. Value engineering is a common and successful approach to design when there are limitations on the project that must be observed. For instance, when the front facade of a multifamily project requires a more creative and contemporary design with large fenestration, narrow frames, and metallic finish, aluminum framed windows are likely the best and only solution. These public-facing choices may be cost-prohibitive to specify for the entire project, so more affordable vinyl windows may be used for discreet areas, such as the back of the building. While both materials can deliver relatively strong energy efficiency, durability, and performance attributes, vinyl frames are not structurally capable of supporting the weight of larger glass systems, which is not an issue for extruded aluminum frames, even with thermal breaks.
The value engineering approach is an important tool when trying to meet overall building performance goals, for instance in California’s Title 24 requirements, where “trade-offs” are allowed between building components.
Photo courtesy of All Weather Architectural Aluminum
Trends indicated buyers and renters are looking for increased square footage inside private spaces to allow for work-from-home and entertaining.
A SHIFT IN DESIGN
Design innovations in multifamily housing are evolving both inside and out. Modern buyers and renters are becoming more aware of how their living space impacts their health, wellness, emotional balance, and social interactions. To this end, buyers are starting to seek out properties with alternate floor space plans, biophilic accents, and a different focus on the type and style of amenities. For the architect, these changes in attitude about the dwelling space are driving design and material specifications in the multifamily market.
The Work-From-Home Occupant
Modern trends point to a desire for more space within the home, and the efforts include finding better ways to use spaces in the structure. Even before the Covid-19 pandemic, the home office was becoming an oft-required staple for renters and buyers. Since the pandemic, many companies have found an increase in productivity from employees who work from home, and an opportunity to scale back on office space by offering either fully remote or hybrid working environments. A recent survey by the Bureau of Labor Statistics found that around 27% of the U.S. workforce was working remotely at least part-time, and information from the Pew Research Center highlights that about a third of workers with jobs that can be done remotely are working from home all of the time, up from only 7% before the pandemic.
Multifamily units are the ideal solution for a work-from-home generation hoping to downsize, skip the commute, and simplify their lifestyle. The challenge resides in trying to accommodate this new lifestyle, as buyers are prioritizing new and different aspects of interest in a multifamily home.
First, a dedicated workspace or ideally a separate home office is a must for many. Teleconference calls from the kitchen table are a thing of the past. Productivity and privacy are fundamental for work-from-home occupants, yet to incorporate this into a standard design can be a creative challenge for the architect. Home offices must meet the same egress requirements as bedrooms per the International Residential Code (IRC), however, work areas without a door may provide a design solution. A flexible home environment may include movable partitions, curtained areas, or line-of-sight changes that can provide privacy but also allow easy access to the rest of the living space.
Another option to increase per-unit square footage is to simply reduce the overall number of units in a project. Although counterintuitive to the idea that more units equals higher returns, building owners have found that reducing the number of units can be a windfall financially. Larger floorplans can demand a higher premium per square foot, meaning the overall average price of units will rise. Fewer units can increase the total amount of square footage per project. Fewer units also put less demand on parking, heating and cooling systems, and amenities.
To increase square footage per unit, a final option is to forgo some of the traditional communal spaces and amenities offered. This approach follows recent trends in multifamily building that suggest occupants are less interested in sharing spaces outside with their neighbors, and that people tend to socialize more in private individual units. While a dedicated gym or workout area is still a popular attribute for buyers, spaces like conference rooms, lounges, games rooms, and communal kitchens tend to be underused. A more common solution is to create a separate center for these amenities, though. A stand-alone amenities center can prove ideal to maximize unit capacity and help manage noise and activity levels within the multifamily complex. This approach can facilitate more popular trends for occupants that include pet-friendly features like pet washing stations or fenced off-leash areas.
Selecting alternative amenities can also be a way to reduce overall energy use and maintenance for the building. Instead of installing a rooftop swimming pool or barbecue area, for example, switch to a living green roof offering residents a community garden. Creative alternatives can drastically reduce energy and water use, minimize maintenance, and attract occupants who are looking for a more non-traditional approach to renting or homeownership.
Photo courtesy of All Weather Architectural Aluminum
In the multifamily environment one of the key methods of incorporating a more biophilic design is to invite more natural daylight into the living spaces.
Photography by Robert Tsai; courtesy of HKS
Access to the outside of the building through large operable fenestration or multi-panel sliding doors enables occupants to connect better with fresh air and daylight.
Designing for Daylight
Whether as a response to the work-from-home trend or simply as a desire to incorporate nature and light into the home, biophilic design is becoming more prevalent in multifamily projects. Biophilic design is the incorporation of nature or natural elements into the built environment. The result is a better connection between people and the planet, which has been shown to improve mood, concentration, health, productivity, and even sleep cycles.
In the multifamily environment, one of the key methods of incorporating a more biophilic design is to invite more natural daylight into the living spaces. Thomas Ehret, Regional Sales Representative for All Weather Architectural Windows and Doors, has noted this shift in the priorities of buyers and renters when it comes to multifamily dwellings and nature or the outdoors. “The trend is really going towards larger windows, bigger views, and more light coming into the home,” says Ehret. “Everybody wants thin sight lines and more openings for glass. From the inside, it means better views and lots of light, from the outside it can work to express more of an architectural design for a project.”
Requesting larger windows and more light is not a simple design alteration, and comes with consequences, especially when trying to improve building energy performance. “Larger windows offer better buyer appeal and rental appeal for the end user who’s going to be living in that particular apartment or townhouse, but the challenge is to attain the same energy performance capabilities of smaller fenestration units,” Ehret says.
Expansive views require thinner frames to allow for more glass. Extruded aluminum frames are ideal for this application. Aluminum is strong enough to incorporate multi-pane windows or IGUs with minimal framing requirements. With the advancements in thermal breaks and warm-edge spacers, modern metal framed windows can easily satisfy U-rating requirements.
Access to fresh air and the outdoors is also trending in multifamily design, especially for units with a patio, balcony or terrace. According to Ehret, French doors and sliding doors with multiple panels remain of strong interest to potential buyers. “Multi-slide doors systems are really popular right now. Buyers are starting to gravitate to the ability to open the whole wall and bring the outside in, especially on the ground floor if there is a courtyard with greenery. It’s very soothing and I think it reminds them of a Hawai’i trip,” Ehret says.
“The nice thing about aluminum is it offers lots of design flexibility in terms of look, color, and customization. These frames can incorporate easily with whatever rainscreen or exterior cladding system,” he points out. “We see projects today that allow tons of natural light, have operable windows to bring fresh air and improve indoor air quality, offer very wide views and all the while hit performance targets. The innovations in the fenestration industry today are amazing.”
Photo courtesy of All Weather Architectural Aluminum
Thin-shell concrete tunnel-form system with modular aluminum formwork.
INNOVATIONS IN THE BUILDING PROCESS
In this article, innovations in multifamily design have so far focused on benefits to the occupant and building owner, but there have been significant steps forward in the construction of multifamily projects, as well. New onsite building systems that enable an efficient and repeatable building process, as well as the rise of modular off-site construction, both offer builders the opportunity to streamline the construction process like never before.
Building Better─Faster
Thin-shell concrete load-bearing tunnel-form systems crafted with modular aluminum formwork have greatly reduced the cost of construction and reduced build schedules to allow for more creative design options. This method involves creating monolithic concrete structures, where walls and slabs are cast simultaneously using modular aluminum formwork. The term “tunnel” refers to the shape and method used to form the concrete walls and slabs in one continuous pour. The tunnel-form system involves large, reusable formwork units that are shaped like half-tunnels or U-shaped molds. These molds, sometimes prefabricated to exact specifications, are positioned on-site to create both the vertical walls and the horizontal slabs of a building simultaneously, resulting in a monolithic concrete structure.
After the concrete cures, the formwork is removed and reused for the next section, advancing through the building floor by floor. The formwork system allows for rapid construction and increased accuracy in creating durable and consistent structural elements.
Before the advent of thin-shell concrete load-bearing tunnel-form systems, traditional construction methods for low-rise multifamily buildings typically relied on a combination of reinforced concrete frames and masonry infill, steel frames with cladding systems, or stud framing using wood or steel.
While reinforced concrete or steel frame systems provided a solid structural frame, they required longer construction times due to the need for multiple stages of framing, masonry work, and finishing. In addition, traditional non-insulated concrete systems were more prone to thermal bridging, leading to an overall increase in energy consumption for heating and cooling. Construction methods onsite were also often wasteful, generating more debris and requiring more material compared to modular systems used in modern tunnel-form methods.
The use of modular aluminum formwork ensures precision in construction, which minimizes gaps, cracks, and thermal bridges that can lead to energy loss. As the formwork is reusable, it reduces construction waste and supports environmentally friendly practices. Because the forms are aluminum, they are durable, lightweight, and 100 percent recyclable at the end of life. These systems also allow for better integration of modern insulation materials, further improving the overall energy efficiency of the buildings.
Photo courtesy of Autoval
Automation and robotics in panel manufacturing facilities have reduced both construction schedules and call-back issues.
The rise of Automation
An important advancement in multifamily construction is the automation of prefabricated and panelized facade systems. This innovation allows manufacturers to streamline the production of factory-built panels, enhancing both the speed and thermal efficiency of construction. The result is a significantly shorter construction timeline, reduced dependency on skilled labor, improved quality control, increased safety, and more efficient integration of materials like aluminum into building envelopes or rainscreen systems.
For the architect, the process of designing prefabricated panels enables a great deal of creative expression in the facade while also supporting performance goals and helping the builder. Panels come pre-assembled with key elements such as moisture barriers and exterior finishes thanks to advanced manufacturing techniques. This approach offers less reliance on weather conditions and a more predictable construction timeline, minimizes on-site labor, and ensures that the building components meet high-performance standards.
While offsite construction of building components has been around for decades, most notably in framing systems, one major innovation to the process has been the inclusion of robotic or automated panel manufacturing.
An advantage of robotic automation is its ability to reduce production time. Robotic automation reduces labor dependency, addressing challenges related to skilled labor shortages in construction. This allows manufacturers to produce complex facade systems with fewer human resources while maintaining high standards of safety and quality. It also enables the integration of complex designs, such as curved or custom-shaped panels, which would be challenging and time-consuming with manual processes.
Another benefit of automated panel manufacturing is the overall thermal performance of the units. Tasks like cutting, assembling, and installing elements such as window frames, insulation, and cladding can now all be done with the precision of robotic systems. Design elements like thermal breaks and enhanced air sealing can be consistently and repeatably manufactured. For the builder, this can mean that all building envelope components can be code-compliant before they arrive on the jobsite.
“There are so many benefits for builders when it comes to panelization,” notes Ehret. “It saves on time, it saves on labor, it increases safety during installation.” After being built in a factory, the finished product can be taken apart, brought out to the building site, and put up successfully in days instead of months or even years in some cases. “With the integrated fenestration, modular companies can include all glass entrances, aluminum frame doors, slider windows, and really anything the architect can design,” Ehret says.
The shift towards prefabrication and modular construction has transformed the way architects approach building design. Prefabricated exterior panels simplify the process of achieving a high-performance building envelope by providing complete assemblies that include all necessary elements, from air barriers to exterior cladding. For architects, this means that design time can be spent focusing on architectural aesthetics and performance goals rather than managing the complexities of coordinating multiple trades on-site.
CONCLUSION
The low-rise multifamily housing market has evolved significantly in response to shifting occupant needs, technological advancements, and a growing emphasis on energy efficiency. Innovations in prefabrication and modular construction have further transformed the industry through the use of robotics and automation.
Buyers and renters in the multifamily market today are seeking homes that are comfortable, energy-efficient, larger, and that can provide greater access to daylight and the outdoors. These trends coincide nicely with the automation of panelized systems capable of prefabricating larger panelized systems that incorporate larger window openings while not diminishing building performance.
Of the ingredients necessary to create the best of both multifamily worlds – an energy-conscious and aesthetically comfortable home – aluminum remains a popular choice in the specification of windows and door framing. The natural attributes of aluminum work in harmony with energy efficiency goals, especially when proper thermal breaks are installed to support more sustainable buildings. At the same time, the thin frames of aluminum create the opportunity to invite more sunlight into the living space, helping address the full range of biophilic needs of the home’s residents, and the work-from-home community. Innovation, faster building, and the rise of automation have all worked in tandem to benefit these developments.
END NOTES
1https://www.nahb.org/Other/Consumer-Resources/Types-of-Home-Construction/Multifamily 2https://www.energy.ca.gov/sites/default/files/2022-08/CEC-400-2022-010_CMF.pdf
Andrew A. Hunt is Vice President of Confluence Communications and specializes in writing, design, and production of articles and presentations related to sustainable design in the built environment. In addition to in-structional design, writing, and project management, Andrew is an accomplished musician and voice over ac-tor, providing score and narration for both the entertainment and education arena. www.confluencec.com. www.linkedin.com/in/andrew-a-hunt-91b747/.
