Last week at Facades+ Boston, hosted by AN in collaboration with AECOM, a roundtable brought together Alejandra Menchaca, founder of the energy and code consulting firm Airlit Studio; Felipe Francisco, senior architect and head of technical design at Studio NYL; and Shu Talun, associate principal at RDH Building Science. The conversation—moderated by Gretchen von Grossmann, managing principal of AECOM Buildings + Places in Boston—looked at how the Massachusetts Stretch Energy Code is evolving the way architects, engineers, and facade consultants design building envelopes.
Across back-to-back mini-presentations followed by a Q&A, the panelists shared how new requirements for thermal bridging, envelope backstop calculations, and spandrel modeling are driving earlier collaboration, more precise detailing, and new tools for achieving both energy performance and design intent. Kicking off the session, von Grossmann borrowed a mantra from Paul Ormond, an engineer at the Massachusetts Department of Energy Resources who had presented earlier in the day: “Crush the space-heating thermal load to oblivion.”
For von Grossmann, energy and resource conservation have become the “fourth dimension” of facades, demanding equal attention to operational and embodied carbon. With the Stretch Code as the backdrop, the speakers offered a grounded look at what’s changing in the design process.
Alejandra Menchaca: “Start with the window wrap”
“I spend a lot of time explaining what the Stretch Code actually means,” Menchaca began. It now requires teams to perform TEDI (thermal energy demand intensity) modeling and envelope backstop calculations, an exercise that derates—or effectively lowers—assemblies by accounting for linear and point thermal bridges. In real projects, she’s found about a 25 to 30 percent derating across the board. “That R-20 wall you used to brag about? It’s probably R-14 once you count edges and penetrations,” she said.
The fenestration-to-wall intersection, or “window wrap,” is almost always the biggest offender. Instead of reflexively adding insulation, she urged architects to start with glazing performance and those linear details. “Passing your envelope backstop doesn’t mean you’ll pass TEDI,” she added. “Do them in parallel, and start early—during the concept phase if you can.”
Felipe Francisco: “Make the model do the talking”
Francisco described how Studio NYL has retooled its process so that performance data informs design in real time. “We start with sketches at the table—analog first, then high-fidelity Rhino and Revit models layered with NFRC and backstop data,” he said. But spreadsheets of psi values aren’t much help in design meetings, so his team built Rhino/Grasshopper scripts that visualize energy performance as geometry. “You can spin the model, adjust glazing ratios, see where heat loss spikes—it’s a way to have a real conversation,” Francisco said.
On one recent project with roughly 30 percent glazing, the team found half of all annual transmission losses through glass and about 41 percent through thermal bridges, with 60 percent of that around windows. “It’s a wake-up call,” he said. “The beauty is, the same model that helps us design exports directly into our permit reports. It keeps the feedback loop intact.”
Shu Talun: “Spandrels aren’t fillers anymore”
Talun focused on the part of the facade that often gets the least design love: the spandrel zone. Under the new code, he explained, designers must back up performance claims with validated 3D thermal analysis, since heat moves through both vertical and horizontal mullions. “A section that looked like R-25 in 2D modeling dropped to about R-8.5 in 3D,” he said. “That’s not a rounding error—it’s a whole different wall.”
As spandrel zones shrink, the gap between 2D and 3D accuracy grows, and room-side insulation stops helping in narrow slab-bypass conditions. RDH, SGH, and Stantec are now collaborating on a Charles Pankow Foundation study to correlate physical testing with simulation and establish a consistent industry method. “Accurate modeling can shift whole-building energy use by double digits,” Talun said. “Getting manufacturers involved early is the key to avoiding those multi-planar losses.”
Q&A Highlights
Gretchen von Grossmann (GvG): So, benefits of the Stretch Code. Panelists, what do we think are the biggest advantages?
Alejandra Menchaca (AM): It’s helping us crush that thermal load, but most importantly, it’s making us think much earlier on about how we design buildings and how heat leaks through envelopes. That’s something that used to happen too late in the process. Now, it’s one of the first conversations we’re having. It’s bringing more people into the room earlier—architects, engineers, envelope consultants—all looking at performance as part of design, not as a compliance check at the end.
Felipe Francisco (FF): I agree with that completely. A lot of what’s in the Stretch Code formalizes things that have already been considered best practice. By making them part of the code, it levels the playing field and makes those standards achievable, rather than something we have to fight for. It allows us to move forward and push the design even further, instead of arguing to get the basics right.
GvG: Let me add a related question. Thermal comfort is something that’s evolved because of this code and because we’re building facades differently. But how do we actually quantify that, or communicate it to clients?
AM: For anyone not familiar with it, there’s a web tool called the Payette Winter Thermal Comfort Tool. That tool actually came out of a project I worked on years ago, and the goal was to quantify how facade performance affects how cold you feel near the glass. Back in the day, mechanical engineers would look at a large window and say, “Oh, you’ll need perimeter heating there,” without much data behind it. We started asking, why? What defines that threshold?
So, this tool lets you test how glass performance and glass height affect comfort. If you find that the facade design keeps people comfortable without that perimeter heating, you can potentially eliminate it. That’s a big deal—you’re reducing your mechanical system, your embodied carbon, and your maintenance costs, and you gain an extra foot or so of usable perimeter space. It’s a win-win.
FF: I think it’s also pushing us to reconsider how much glazing is actually needed. The code encourages us to be more intentional about glass—to think about placement and proportion. You can still have great daylight and strong views, but you don’t need floor-to-ceiling glass everywhere. With thoughtful design, you can achieve thermal comfort and still deliver an open, connected experience for the occupants.
GvG: Is the code driving innovation and beauty, or limiting it?
FF: In our experience, it’s actually doing the opposite of limiting. It’s encouraging teams to be more deliberate about where glass goes and how it’s used. Instead of blanket walls of glazing, we’re seeing projects that celebrate specific, well-considered moments—entries, corners, double-height spaces—where glass becomes a feature. The result is often more expressive and technically sophisticated.
Shu Talun (ST): I’d add that manufacturers are very aware of these changes. The Stretch Code is influencing product development. We’re seeing new systems—better frames, better spandrel designs—come to market because of this. It’s been interesting to watch; the market is catching up quickly.
GvG: Let’s talk about embodied carbon. How are you addressing that?
ST: Once we’ve achieved operational targets, embodied carbon is really the next focus. There are so many options now—mass timber panels, precast, light-gauge steel—and the differences can be surprising. On one project, we compared a large steel-stud mega-panel with a precast wall and found the precast actually had less embodied carbon because of the composition of the mix. It shows that there’s no single answer; you have to look closely at manufacturing, transport, and assembly.
AM: I agree. And it ties back to what I said earlier about “holes in the bucket.” For years, the first question when trying to improve the envelope was, how many more inches of insulation do we need? But that just increases embodied carbon without addressing the actual problem. Now we’re focusing on details—linear and point thermal bridges, window transitions, corners, parapets. Fixing those can reduce 25–30 percent of your heat loss, often without adding material. That’s the biggest shift: we’re improving performance through smarter detailing, not thicker walls.
GvG: What does this all mean for all-glass buildings in Massachusetts? Is there still hope for them?
FF: Realistically, we’re going to see a reduction in the overall glazing ratio with current technologies. But that doesn’t mean we’re losing transparency or design quality. You can still create buildings that feel open and light; it just comes down to how the glass is distributed and integrated. It’s more about composition than percentage.
ST: The challenge isn’t so much the glass itself—it’s the framing. For low- to midrise projects, you can work around that with panelized or stick-built systems. But for highrise buildings, where unitized curtain wall makes sense, we’ll need continued innovation to improve frame performance. The delivery system isn’t going away; we just have to make it better.
AM: And let’s be honest—if you walk around Boston, most of those all-glass buildings already have the shades half-down all year. That tells you something about comfort. The Stretch Code is forcing a conversation about why we want so much glass, and where it actually adds value. It’s a more nuanced way to design.
GvG: Okay, audience questions. Here’s one: Do shadow-box spandrels’ solar gains get counted?
ST: Not really, no—not in the reported calculation. That’s why modeling scope is so critical. When we use 3D thermal modeling, we can actually capture those multi-directional heat flows and understand where the bridging happens. 2D models just can’t show that.
GvG: Will we see more double-skin or closed-cavity facades in the future?
FF: We study them all the time, and they’re always fascinating, but they’re still rare in practice. The performance gains don’t always offset the cost or complexity. When they get built, it’s usually because a project has other goals—acoustics, daylight modulation, or visual expression—not just energy efficiency.
AM: I’d add that double-skin systems can absolutely help with solar control and occupant comfort, but if your goal is strictly to hit a target U-value under the Stretch Code, it’s not the magic solution. You’ll get more out of improving your glazing and your details.
GVG: Here’s an interesting one. Is LEED obsolete?
AM: No, not at all. The Stretch Code overlaps with parts of LEED, but they focus on different things. The code is about performance—energy and envelope—while LEED looks more holistically at materials, health, and sustainability. If you meet the Stretch Code, you’re already well on your way to LEED compliance.
FF: Exactly. Think of the code as your baseline—your minimum for energy and performance. LEED is still valuable as the broader sustainability benchmark. One doesn’t replace the other; they work together.
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