Building envelope design in healthcare goes beyond energy efficiency

Why is the building envelope important?

The building envelope is what separates the interior and exterior environments. It keeps the elements (wind, rain, snow) out and acts as a thermal barrier. The building envelope helps maintain environmental control of the indoor space. It affects things like: temperature, humidity, ventilation, natural light, and air quality.

A building’s envelope is made up of walls, windows, doors, and roofs. In healthcare, we often see components like curtain walls, concrete masonry, and steel stud walls making up the envelope. And the envelope has an aesthetic function, too.

Healthcare demands a bit extra from the building envelope

Healthcare facilities require tight control of temperature and humidity to promote health and recovery. Healthcare is an essential service, so the healthcare building envelope needs to be extra durable. An ideal healthcare building envelope should last a long time; and it should avoid a lot of downtime for service and maintenance.

In recent decades, the trend in healthcare has been towards more sustainable high-performance building design. First, the industry focused on reducing energy costs; then, we started looking at energy efficiency and cutting building energy use. After that, the goal was to reduce greenhouse gas emissions; first, we focused on decarbonization studies that looked at operations, now, we think about embodied carbon.

Our teams have long recognized that decarbonizing healthcare is more complex than simply electrifying buildings. We’ve written before about smart decarbonization—an approach that balances emissions reductions with reliability, resilience, and patient safety. That thinking is even more critical today.

Healthcare designers now face growing pressure to cut carbon while working within tight capital budgets. In Canada, funding typically goes first to clinical needs. Decarbonization must then fit within what remains.

Higher performance design often comes with additional costs. It’s natural for decision-makers to ask these types of questions: What are we getting from this? Does it help with energy efficiency? Does it help us hit our energy targets?

In healthcare facilities, ventilation requirements account for the majority of energy use. So, improvements to the building envelope often have limited impact on energy targets. The result is that envelope upgrades have been deprioritized. We often see healthcare projects choose a wall design simply because it hits an effective R-value for insulation performance to meet energy targets and budget.

However, healthcare design is ever more concerned with thermal comfort. We believe designing a space that’s inherently more comfortable is better than relying on the HVAC system to create those comfortable conditions—and likely drive up carbon emissions. When we look at thermal comfort in this way, building envelope design is much more important.

We believe the conversation about the building envelope needs to be more nuanced, and the design more holistic. What kind of space is it? Is it acute care or a medical office? What are the ventilation needs? Because these factors drive energy use.

What’s possible in the envelope for a hospital?

On a recent healthcare design project, we had the opportunity to pursue a carefully considered approach to the building envelope. On this public-private partnership (P3) project, we are serving as the PDC (planning, design, and construction) consultant. We had a chance to talk about windows and thermal comfort.

In healthcare design, windows are important. When it comes to inpatient units, designers want to use windows to create a connection to the outdoors. This connection has been shown to benefit those inside the building. As envelope designers, we need to consider the placement of windows, plus their shape and orientation. How much window area do we have versus wall area? We must balance the windows’ impact on the overall envelope with creating a visual connection to the outside, providing access to daylight, while balancing thermal comfort and avoiding condensation.

When we modeled the energy use for this P3 acute care hospital in Canada, we looked at using a higher-performance envelope with more insulation and triple-pane windows. That approach didn’t lower energy use much—because, as we said, in this kind of building, ventilation uses the most energy.

We wanted to have an efficient, low-carbon HVAC system, which means we are using low-temperature heating. We preferred to avoid perimeter radiators because they use high-temperature water. And they usually need boilers. High-temperature heat pumps are an option, but right now they’re expensive.

So, we asked ourselves what kind of envelope design would allow us to get rid of perimeter radiators? We studied thermal comfort in relation to window and diffuser placement. We looked at the window shape and orientation.

The wide window design would require more diffusers and radiators. By making the windows narrower and taller, we were able to reduce these requirements.

Using tall, narrow windows made it possible for us to reduce the HVAC system requirements and install fewer diffusers to control condensation on the project. A wider window design would require a longer run of diffusers. We were able to adjust the building envelope design and design the window placement for thermal comfort without using perimeter radiators.

This is just one example of how better buildings come from holistic envelope design.

Holistic envelope design has additional benefits

Building envelope design in healthcare should consider more than just energy efficiency. Other factors include:

• Durability
• Thermal comfort
• Airtightness
• Resilience
• Occupant wellbeing

In this approach, the design team tries to balance all of those points alongside a connection to the outdoors—and, of course, the budget.

Here is a look at other factors.

Thermal comfort: As we shared above, getting the the window placement and sizing right can help improve efficiency and reduce energy use. A high-performance building envelope can result in a building that’s less reliant on systems for thermal comfort.

Efficient systems: An airtight building envelope has benefits for decarbonization and energy use. It helps keep the cold or warm air in, so systems don’t need to work as hard.

Effective insulation and windows that resist heat transfer are important. But improving the airtightness of the envelope can help reduce a building’s EUI (energy use intensity).

Acoustic comfort: An airtight envelope is also quieter. This results in greater acoustic comfort in patient areas.

Environmental control: An airtight envelope also keeps out pollutants and particulate matter. For example, wildfire smoke has been an issue in recent years, especially in Canada. In 2023, Canadian wildfire smoke increased hospital visits for heart and lung issues thousands of miles away in Maryland. No one wants to breathe those particulates, especially if you’re in the hospital.

A good way to limit exposure is to have an airtight building envelope. But a lot of existing buildings aren’t very airtight; they weren’t designed to be airtight. To control particulates, the operators typically pressurize the building by blowing air out to keep particulates from entering the building. Blowing all this air just intensifies building energy use and operational costs. A good envelope will keep out particulates.

Take an integrated approach to building envelope design

How can we avoid suboptimal, prescriptive solutions and embrace more holistic approaches? Early collaboration is the key.

With project goals in mind, integrated design teams can work with building performance specialists to make more nuanced decisions about envelope and façade design. For building owners, it’s important to bring in your envelope and sustainability specialists early in the design process. This way, your team can make informed decisions about the façade and envelope rather than retrofitting solutions after architectural concepts are set.

There is no single “right” solution for building envelope design. When we make it part of the design process, we can support many project goals such as sustainability, occupant comfort, and operational efficiency. By taking a flexible, context-sensitive approach to envelope design rather than a budget-driven option, we can design buildings that meet complex needs.

While ventilation loads often take the high-performance building envelope out of the healthcare conversation, we shouldn’t forget about it. Energy models alone are insufficient for guiding healthcare envelope decisions. Thoughtful design can enhance resilience and comfort in a variety of building types.

Building envelope design should be an outcome of an integrated process that brings together architects, engineers, and building scientists. The skin is just as important as it sounds.