Written by: Jenn Pratt

From construction to operations, the built environment accounts for more than 38 percent of carbon emissions in the U.S. Amid increasing concerns over climate change, public sector demand for more sustainable buildings and growing awareness of social responsibility, the construction industry is grappling with how to reduce its environmental impact and play a role in a more sustainable future.

As recently as ten years ago, sustainable buildings were viewed as experimental but today, are becoming more feasible. And still, owners and project stakeholders are often forced to choose between sustainability and cost. An owner may have ambitious sustainability goals but if the cost of bringing them to life is too high, they may be out of reach.

We’ve seen this happen time and again. Designers, engineers and contractors work to accommodate an owner’s environmental goals but run into problems when pricing comes into play. Often, green features push the project over budget and realizing the building can’t generate enough rent to satisfy the proforma, the owner asks the team to come up with a less costly option. In doing so, green features are cut one by one until the project is within budget, but far less sustainable.

Progress Through Innovation

Through advances in technology and innovative approaches to construction, sustainable buildings today don’t have to cost more. Beginning in the earliest design phase, all the way to operations, sustainable buildings are becoming a reality without breaking the bank through:

Collaboration: Waste in the construction industry has been an ongoing problem. However, through early engagement, whether during pre-design or schematic design, owners, architects, engineers and contractors can reduce rework and wasted materials. Constructible BIM solutions and collaboration platforms make it easy to share real-time project data across teams. Using these solutions to work together throughout the design and construction process, problems that could lead to higher costs, delays and material waste are identified and resolved before it’s too late.

Building Performance Analysis: Recent advances in building performance analysis tools allow design professionals to explore the energy impact of various design features. For example, they can quantify the energy savings exterior shading elements on the windows or electrochromic glass may provide. The ability to test concepts at the beginning of a project and collaborate with the entire team to find sustainable options that are also within budget can eliminate the need to choose between cost and sustainability.

Additionally, considering how a building will be occupied can eliminate unneeded space and thus, reduce the amount of energy required to cool, heat and light it. These cost savings can then be invested in sustainable features such as lighting controls or exterior sun shading devices. 

Prefabrication: Offsite manufacturing, also known as prefabrication, has grown in popularity for its ability to deliver cost and schedule certainty but could it also help deliver more sustainable buildings? Building off-site in a controlled environment reduces material waste and a streamlined manufacturing process is more energy and labor efficient. Advances in prefabricated facade systems not only change how structures are constructed, but also optimize their core integrated systems to maximize energy efficiency and performance, and occupant wellness and comfort.

Radiant Systems: Heating and cooling, and hot water, account for nearly half of global energy consumption in buildings. Recent research conducted by the Center for the Built Environment demonstrates how heavy thermal mass radiant heating and cooling (radiant in concrete floors) can leverage milder water temperatures to considerably reduce the energy needed to heat and cool buildings.

In a heavy thermal mass radiant solution, heating and cooling energy are delivered to the slab using water. This water heats or cools the slab.  The slab then radiates this heat or cool into the surrounding space. 

Concrete is great at storing and holding energy. If you’ve ever spent a summer evening on a slab that was in the sun all day, you know that hours later, it still feels warm. Unlike traditional systems that are designed to maintain comfort during the worst hours of the worst day, a heavy thermal mass radiant system can leverage the mass of the building itself to store heating and cooling energy and release it slowly into the space. The system essentially turns a building into a battery.

This opens up a world of green opportunities. By storing energy in the slab, a building operator suddenly gets to choose when to use that energy. For example, if the goal is to use solar energy to cool the building, only run chillers during hours of sunlight. Or, if the aim is to halve the size of all-electric heating and cooling plants, equipment is sized for the average heating and cooling demand over the day and the slabs store the excess until it’s needed.

Accelerating the Path to Zero

Industry conversations around embodied carbon have increased tenfold in recent years and for good reasons. Building materials represent nearly a third of the construction industry’s embodied carbon. When it comes to materials, concrete isn’t always viewed favorably. In fact, cement, the glue that holds concrete together, is alone responsible for 7% of the worlds CO2 emissions.  At the same time, concrete is the most widely used man-made material in the world. While concrete is often characterized as our biggest problem, it may actually be our biggest opportunity. Concrete is durable, long-lasting and its thermal stability can lead to more energy efficient buildings and facades.

Low carbon solutions for concrete exist today. In fact, some have been used successfully for 40 years. These solutions make use of materials called Supplementary Cementitious Materials (SCMs), which are often post-industrial waste products such as flyash (a by-product of the coal industry) and slag (a by-product of the steel industry).  These materials, which can replace a portion of the cement in concrete, are not burdened with high amounts of CO2 and actually improve the concrete’s performance. The only downside is that SCMs can slow down the curing process, causing the concrete to gain strength more slowly.

Historically, the construction industry has refined building design with only a single driving variable – cost. In efforts to simplify formwork, structurally inefficient systems emerged that save labor but use more material. Efforts to accelerate construction lead the development of mixes that can achieve high strengths in only a few days. These practices combined result in buildings that use more concrete and concrete mixes that use more cement.

Today, the industry must consider a second variable in building design – CO2. As the industry optimizes designs around this new two variable system (cost and carbon) it can’t simply take a traditional design, toss in some SCMs and call it sustainable. It’s time for the industry to completely rethink the way it builds.

In 2018, Clark Pacific did just that. Starting with a blank canvas, the company established a two variable approach and evaluated dozens of potential designs for cost and carbon. Concrete volume was carved out by thinning slabs and adding ribs to achieve the same strength with less.  Ribs were made wider to reduce the early strength requirements of the concrete and enable higher SCM mixes. Offsite fabrication allows for the use of a form heating system that accelerates early strength gain. This allows for the removal of up to 70 percent of the cement from mixes. The heating system removes roughly 20 times the carbon from the mix than it took to heat the forms.

This aggressive approach removes roughly 20 percent of concrete from the building and the remaining concrete has 45 percent less carbon when compared to 2019 National Ready Mix Concrete Association Baseline mixes for similar strengths.

The system also incorporates an offsite manufactured heavy thermal mass radiant heating and cooling system built integral with the floor system and delivered to the site complete with distribution piping and controls.  The overall solution results in removal of half the carbon from the concrete, 30 percent less electricity over traditional all electric air-based solutions at a price that is competitive with conventional low performance buildings. 

Looking Ahead

As individuals and industry professionals, we should all consider the fundamental design, whether it’s concrete, steel, timber or precast, with both cost and carbon in mind. The advances in technology, materials, systems and processes captured here are encouraging first steps. Together, we can all pave the way to a greener, more sustainable future.