We are thrilled to announce that Emu’s comprehensive training programs are now officially accredited by the American Institute of Architects (AIA). This milestone means that design professionals can now earn valuable Passive House AIA CEU credits while mastering high-performance construction.
If you are looking for meaningful Passive House architect continuing education, our programs offer a unique opportunity to elevate your practice. We focus on delivering practical, actionable knowledge that transforms how you design and build.
Bridging the Gap Between Design and Construction
The construction industry often suffers from a disconnect between design intent and on-site execution. We created our proprietary Passive Design/Buildâ„¢ core curriculum to solve this exact problem. This curriculum intentionally brings architects and designers together with builders, general contractors, and other construction professionals under one roof.
By training these groups simultaneously, we establish a shared language and a unified understanding of high-performance standards. This integrated approach delivers genuine AIA applied building science. Instead of theoretical concepts that fail in the field, you learn architect applied building science that translates directly to successful project outcomes. You will leave with a clear roadmap for how to execute complex details effectively.
Flexible Formats for Every Schedule
We understand that working professionals have demanding schedules. To make our Building Science AIA CEU credits accessible, we offer our certified Passive House training in three distinct formats:
Online Course: Master the fundamentals of high-performance design at your own pace from anywhere.
In-Person Boot Camp: Immerse yourself in an intensive, fully practical environment. This is the ultimate AIA hands-on training experience, allowing you to practice critical building techniques physically.
Hybrid Boot Camp: Combine the flexibility of online learning with a concentrated, in-person workshop. This format offers excellent AIA CEU hands-on training while minimizing your time away from the office.
Whether you prefer digital learning or dedicated Architect hands-on training, our formats are designed to help you meet your professional development goals efficiently.
Deepen Your Building Science Knowledge
Beyond our core certification courses, Emu offers a wealth of ongoing resources. We host free presentations and specialized online webinars designed to provide in-depth content on targeted topics. These sessions are perfect for professionals seeking consistent building science architect continuing education without a massive time commitment.
Don’t just take our word for the impact of this integrated education. Read how our alumni are transforming their careers and delivering superior buildings on our testimonials page.
By joining Emu’s training programs, you are not just checking a box for continuing education. You are joining a collaborative community of forward-thinking professionals dedicated to building a better future. Explore our AIA-accredited courses today and take the next step in your high-performance building journey.
California AB 368 Passive House Compliance Could Transform Building Efficiency Standards
On May 30, the passing of California AB368 Bill marks a significant milestone for the adoption of Passive House in the State, and across the Country.
In a major move toward improving building performance and reducing carbon emissions, California Assembly member Chris Ward has introduced AB 368—a bill focused on advancing California AB 368 Passive House compliance. This legislation tasks the California Energy Commission (CEC) with evaluating Passive House standards as a potential alternative pathway to the state’s Title 24 energy code.
What Is California AB 368 Passive House Compliance?
California AB 368 Passive House compliance refers to the potential approval of Passive House standards as an alternative method to meet California’s building efficiency requirements under Title 24. If adopted, this could give architects, builders, and developers more flexibility in achieving energy efficiency goals through a performance-based framework rather than prescriptive measures.
Why It Matters for California
This push for California AB 368 Passive House compliance comes at a time when the state is grappling with severe climate challenges—including wildfires, extreme heat, and water shortages. Passive House buildings are inherently more resilient, healthy, and energy-efficient, making them a strategic asset in addressing both environmental and public health goals.
The bill is sponsored by Climate Action California, an organization advocating for bold climate solutions. Its introduction reflects a growing recognition that traditional building codes may need to evolve to support deeper energy savings and long-term climate strategies.
How Did We Get Here?
The Climate Action California organization has lead the charge in promoting the AB368 Bill to make Passive House compliance a reality for California. Emu, Passive House California, and other likeminded organizations have supported the bill.
Looking Ahead
If adopted, California AB 368 Passive House compliance could pave the way for more sustainable construction practices across the state. By integrating Passive House design into the regulatory framework, California has an opportunity to lead the nation in energy-efficient building innovation—while offering residents safer, healthier, and more climate-resilient homes.
Find out what other free building science presentations we have planned over the Summer, including a panel discussion with Passive House builders on September 9.
Join us this Summer for a great series of free in-depth webinars and in-person social events. Deepen your knowledge of building science and Passive House and building science, and network with other professionals across the U.S.
HB 1183: A Key Step for Passive House in Washington
Washington State has recently passed HB 1183, a landmark bill aimed at supporting Passive House construction. This bill addresses major challenges in building energy-efficient homes by reducing barriers in local zoning and building codes. By making it easier to implement Passive House standards, Washington is paving the way for more affordable and sustainable housing.
With HB 1183, Washington becomes a leader in promoting green building practices and energy-efficient homes. These homes, built to Passive House standards, use up to 90% less energy for heating and cooling. As a result, they provide significant savings on utility bills while helping reduce carbon emissions statewide.
Key Features of HB 1183 for Passive House Construction
HB 1183 includes several important revisions that make it easier and more affordable to build Passive House projects. By addressing obstacles such as building height limits and setback requirements, the bill supports energy-efficient designs. Additionally, it helps developers and architects streamline their projects.
The changes are essential for making Passive House construction feasible in urban areas. They simplify the design process and reduce unnecessary costs, which makes it easier to prioritize energy performance without sacrificing affordable housing goals.
Key Changes in HB 1183
HB 1183 introduces several major changes to building regulations, aimed at supporting Passive House development:
Wall Projections: Insulated walls can now extend 8 inches into setbacks, even for non-conforming buildings.
Roof Height Increases: Buildings can exceed height limits by 8 inches to accommodate insulation; 4 feet for solar panels.
Parking Requirements: Onsite parking is no longer mandatory for permit approval, making development more affordable.
Facade Modulation: Facade modulation and upper-level setbacks are no longer required, reducing unnecessary costs.
Floor Area Measurement: Floor area is now measured from the inside of drywall, making thicker walls acceptable.
These changes directly address the barriers that often make Passive House construction impractical, especially in densely populated cities. By relaxing restrictions, Washington State is taking an essential step toward energy-efficient, sustainable housing.
To find out more about how these changes impact building efficiency, find out more on Emu’s Building Science Blog.
Collaborative Efforts Behind the Bill
The passage of HB 1183 is the result of collaboration between various stakeholders, including Rep. Davina Duerr and experts like Rob Harrison, a Passive House consultant. Their combined efforts, along with input from Dan Bertolet and David Neiman, have made this bill a reality. As a result, Washington is now well-positioned to lead in sustainable housing.
By reducing regulatory hurdles and streamlining the process, HB 1183 is a major step forward in building a more energy-efficient and affordable future for Washington’s residents. This bill not only addresses the current needs but sets a precedent for future legislation in other states.
Xcel Energy Now Reimburses 90% of Training Fees for Emu’s Passive House Boot Camp
Construction professionals in Colorado now have an incredible opportunity to advance their skills, thanks to Xcel Energy’s reimbursement program.
Xcel is offering to cover 90% of the training fees for Emu’s Passive House Boot Camp. Here’s everything you need to know about this valuable program.
How the Xcel Reimbursement Program Works
If you’re a construction professional working in Colorado and served by Xcel Energy’s electrical service, you’re eligible to receive 90% reimbursement of your Emu Passive House Boot Camp training fees. Here’s how it works:
SUBMIT YOUR APPLICATION for the Xcel reimbursement – one application works for up to 10 team members. Xcel will verify your eligibility. Estimated response time is 3 weeks, so plan ahead.
Enroll in the Passive House Boot Camp: Register for the Denver Passive House Boot Camp. You’ll need to pay upfront in full (payment plans are available at checkout).
Complete the Training: Attend the Boot Camp and successfully complete the course. This training will help you master energy-efficient design and construction techniques that align with Passive House standards.
Submit Your Documentation: After finishing the boot camp, submit proof of enrollment, completion, and payment for the course to Xcel Energy.
Get Reimbursed: Upon approval, Xcel Energy will reimburse you 90% of the training costs, making it an affordable investment in your career and the future of sustainable construction.
Emu’s Passive Pods, used to teach Passive House techniques during a Boot Camp.
Xcel Passive House Training Reimbursement – Eligibility Requirements
To be eligible for the reimbursement, you must meet the following criteria:
Be a construction professional (builder, contractor, architect, engineer, etc.) working in the state of Colorado, within Xcel Energy’s electrical service area.
Enroll in the official Emu’s Passive House Boot Camp.
Provide the required documentation showing that you completed the training.
If you meet these requirements, you’ll receive significant financial support from Xcel Energy to help you gain critical Passive House skills.
Benefits of the Passive House Boot Camp
Participating in the Passive House Boot Camp offers several advantages:
High Demand for Skills: As energy efficiency becomes a priority in building practices, professionals trained in Passive House standards are highly sought after.
Environmental Impact: Learning to build energy-efficient structures means contributing to sustainability by reducing energy consumption and lowering carbon footprints.
Financial Savings: Energy-efficient buildings lower operating costs, benefiting homeowners, tenants, and clients by reducing long-term energy bills.
Career Advancement: With Passive House certification, you’ll be positioned as an expert in a growing field, opening doors to new projects and opportunities.
Little-Known Policy Set to Make Passive House Standard Mandatory Nationwide
WASHINGTON — A Trump-era executive order on energy policy has unexpectedly set the stage for a sweeping transformation of U.S. building regulations. Due to an overlooked legislative trigger, the Passive House standard—one of the world’s most rigorous energy-efficiency requirements—will become mandatory for all new buildings by April 1, 2027.
Originally aimed at restricting Canadian coal imports and Chinese photovoltaic panels, the executive order contained a clause requiring that, in the absence of affordable domestic alternatives, U.S. buildings adopt “the most stringent feasible energy efficiency standards.” Due to ongoing trade restrictions and rising energy costs, this provision has now been automatically triggered, forcing new construction across the country to comply with the Passive House standard—a move that is sending shockwaves through the real estate, construction, and energy industries.
Trump’s Energy Policy and the Passive House Loophole
Signed in 2019, the executive order was intended to prioritize American energy independence, banning imports of Canadian coal and Chinese-made solar panels. However, the order also included a contingency clause mandating that if no viable energy alternatives were introduced, the strictest available energy-efficiency standard would become law.
That standard, as determined by the Department of Energy in late 2024, is Passive House—a European-originated building method that slashes energy consumption by up to 90% compared to conventional buildings. The Energy Security Act of 2023 unknowingly reinforced the provision, linking it to an automatic legislative trigger that went unnoticed by lawmakers until it was too late.
Now, with the April 1, 2027 deadline looming, developers and builders are scrambling to comply with the unexpected energy mandate.
“It’s an energy policy no one voted for, yet it’s happening anyway,” said a senior congressional aide.
Tesla Powerwall Controversy: Elon Musk’s Involvement Raises Questions
A key component of Passive House design is on-site energy storage, often achieved through solar power and battery systems. However, with Chinese solar panels still restricted under Trump’s original order and no clear alternative available, the Tesla Powerwall has emerged as the default energy storage solution for many Passive House projects.
This has raised concerns over a potential conflict of interest involving Elon Musk, whose Tesla Energy division stands to profit significantly from the policy shift. As the U.S. market pivots toward Passive House standards, Tesla Powerwall battery demand is expected to surge, giving Musk’s company an even greater share of the home energy market.
“Musk is uniquely positioned to benefit,” said David Peterson, a policy analyst at the Institute for Energy Transparency. “This is a policy outcome driven by trade restrictions, and Tesla is reaping the rewards.”
Lawmakers, including Senator Elizabeth Warren, are calling for an antitrust investigation into whether Tesla’s market dominance in home energy storage constitutes a monopoly.
Musk, however, brushed off the controversy.
“Powerwalls are great. Everyone loves them,” he posted on X (formerly Twitter). “If the government wants to mandate energy-efficient homes, that’s their choice. But let’s be honest—Tesla makes the best batteries.”
Industry Backlash and Political Fallout
The policy shift has sparked outrage among Republican lawmakers, who argue that the Passive House standard is an overly strict mandate that will drive up construction costs and limit housing development.
“This is the kind of European-style overregulation we were trying to avoid,” said Senator Ted Cruz. “Now, because of some buried clause in an old executive order, every home in America has to be built like a spaceship.”
Meanwhile, Democratic leaders are embracing the policy as an unexpected victory for energy efficiency.
“We’ve been advocating for stronger energy standards for years,” said Senator Ed Markey. “Thanks to this legislative oversight, we’re now moving toward a zero-energy future—faster than anyone expected.”
Challenges for Homebuilders and the Real Estate Market
The U.S. construction industry is facing an unprecedented challenge in adapting to the Passive House mandate. Builders will need to integrate triple-pane windows, advanced insulation, and high-performance air-sealing techniques—materials that are still relatively scarce in the domestic supply chain.
Many developers fear construction costs will rise, potentially pricing out homebuyers. However, advocates argue that energy savings over time will offset initial costs.
“It’s not that Passive House is a bad idea,” said Mike Reynolds, a New York-based architect specializing in energy-efficient design. “It’s just that no one expected this transition to happen overnight.”
Trump Responds: “I Always Supported the Best Houses”
For his part, former President Trump has claimed credit for the unintended consequences of his order.
“I have always supported the best houses,” Trump said in a statement from Mar-a-Lago. “Very strong houses, very energy efficient. Some people are saying I invented Passive House. Who knows? Maybe I did.”
Despite calls from some in Congress to repeal or modify the policy, industry experts warn that the market is already adapting, with builders, suppliers, and energy companies shifting resources toward meeting the 2027 mandate.
Unless Congress acts swiftly, the United States will soon be constructing buildings to the world’s highest energy-efficiency standard—whether it planned to or not.
American construction is currently undergoing a massive and necessary transformation. Builders, architects, and developers are rapidly adopting continuous exterior insulation to meet stricter energy codes and higher performance standards. We insulate our walls better than ever before, wrap our buildings in high-tech weather barriers, and obsess over sealing every tiny crack.
Yet, amidst all this progress, the industry suffers from a massive blind spot. Project teams will spend hours agonizing over minor heat loss caused by a few extra wood studs in a wall assembly. Then, those same teams will turn around and approve a continuous strip of highly conductive aluminum cutting straight through their expensive exterior insulation.
This oversight is costing us dearly. A standard sheet metal flashing detail is perhaps the most overlooked cause of thermal bridging in high-performance construction in America today.
If you want your buildings to actually perform as designed, you must understand why this happens. Let us explore the mechanics behind this massive energy leak, the sheer scale of the problem across different projects, and how to fix it using better materials.
The Rise of Exterior Insulation in America
For decades, American builders relied almost entirely on cavity insulation—stuffing fiberglass batts between wood studs. Building science eventually proved that this method leaves buildings highly vulnerable to energy loss. Every single wood stud acts as a small bridge for heat to escape.
To combat this, the industry embraced the concept of the perfect thermal envelope. By wrapping the entire building structure in rigid foam or mineral wool, you drastically improve energy efficiency and indoor comfort.
However, moving insulation to the exterior means we have to rethink how we manage water. When water gets behind cladding, it needs a way to drain out safely. The traditional solution has always been to insert a piece of metal flashing to kick the water away from the wall. Unfortunately, bringing this old habit into modern wall assemblies creates a massive building science flaw.
The Most Overlooked Thermal Bridge
A thermal bridge occurs when a highly conductive material bypasses a building’s thermal insulation layer. Heat always seeks the path of least resistance. When a conductive material slices through your insulation, it acts like a superhighway for heat to escape your building during the winter and enter during the summer.
When you look for a textbook thermal bridge example, you do not need to look much further than standard sheet metal. Aluminum, copper, and stainless steel are incredible conductors of heat. Even though the metal used for flashing is very thin, its high conductivity means it easily pulls heat straight through the wall.
Think about a gaping, one-inch hole running the entire length of your exterior insulation. Most construction professionals would immediately halt a project to fix such an obvious defect. However, a continuous strip of highly conductive metal does exactly the same thing to your energy performance. This makes the standard metal flashing example the worst offender for breaking a modern high performance building envelopes.
A seemingly innocent flashing detail in a wall assembly using exterior continuous insulation.Isothermic view of the same detail. The metal sheet flashing causes a severe distortion of the isotherms, and a significant thermal bridge.
For comparison, we modeled the thermal bridging caused by leaving an empty gap between the boards of the exterior continuous insulation. From a thermal bridging perspective, we found that the metal flashing detail shown above causes as big a thermal bridge as a 1-inch wide empty gap between the insulation boards.
The wall detail showing the exterior continuous insulation with a 1-inch gap.The thermal impact of the 1-inch gap between insulation boards is comparable to the thermal bridging effect of the metal flashing detail shown earlier.
Thermal Bridging: Mice and Elephants
The American high-performance building sector has a strange double standard. We heavily scrutinize the thermal bridging caused by standard wood framing. Teams will redesign entire structural layouts to eliminate a few extra two-by-fours, adopting advanced framing techniques just to save a fraction of an R-value.
Wood, however, is a relatively poor conductor of heat. While wood studs do cause some thermal bridging, their impact is minimal compared to metal. In other words, in the realm of thermal bridging, wood studs are but little mice compared to the thermal bridging elephants of metal, concrete, and masonry.
On the other hand, the standard metal flashing details often get a free pass with project teams. Installers routinely slide aluminum flashing all the way back to the structural sheathing, cutting completely through the continuous exterior insulation. Because we are so focused on mitigating minor heat loss from wood framing, we completely ignore the massive thermal bridging detail right in front of us. We solve a minor issue while installing a massive energy leak by default.
The Scale of the Problem: Thousands of Linear Feet
You might think a thin piece of metal cannot possibly cause that much energy loss. This assumption ignores the sheer scale of modern construction. We are not just talking about a single piece of flashing over one single exterior door.
In a standard single-family residential build, you might have several hundred linear feet of flashing above windows, doors, and floor transitions. If every single foot of that flashing slices through your insulation, the cumulative heat loss is staggering.
When you scale this up to a large commercial facility or a multi-family deep energy retrofit, the problem multiplies exponentially. These larger projects often feature thousands of linear feet of exterior flashing. When you apply a highly conductive thermal bridging example across thousands of feet, the energy loss forces the building’s mechanical systems to work continuously just to maintain a baseline temperature.
The Consequences: Performance Gaps and Mold
Ignoring a massive thermal bridge detail leads directly to what building scientists call the “performance gap.” This gap represents the stark difference between how a building is modeled to perform on paper and how it actually uses energy in the real world. Performance gap is a particularly sticky point when it comes to high-performance projects, and building electrification (read how Passive House can help you prevent it).
When energy models fail to properly account for the immense heat loss caused by a metal flashing example, the building consumes far more electricity or gas than predicted. This drains the owner’s wallet and puts unnecessary strain on the grid.
Beyond energy loss, this detailing creates serious health and durability risks. When heat escapes through the metal during cold weather, the interior surfaces directly behind the flashing drop in temperature. Warm, moist indoor air hits these cold spots, causing hidden condensation inside your walls. Over time, this continuous condensation creates the perfect breeding ground for toxic mold and structural rot.
Fortunately, you do not have to choose between a waterproof building and an energy-efficient one. You can achieve effective bulk water management without destroying your carefully designed thermal envelope.
The solution lies in adopting proper exterior insulation flashing techniques. Instead of relying on highly conductive sheet metal that penetrates the entire wall assembly, project teams must substitute non-metal alternatives.
A thermal bridge-free alternative flashing detail. In this case, a vinyl flashing profile was used instead of metal sheet.The non-metal flashing profile used in this detail completely eliminates the thermal bridge.
By utilizing rigid fiberglass components, specialized high-density plastics, or high-performance flashing tapes, you can direct bulk water safely away from the wall cavity. These materials provide effective drainage while possessing a fraction of the thermal conductivity of aluminum or steel.
When you specify non-metal continuous insulation flashing, you maintain the full integrity of the exterior insulation. You keep the interior surfaces warm, prevent hidden condensation, and completely eliminate the most overlooked thermal bridge in the country. Start demanding better details on your projects, and stop letting old habits ruin modern building performance.
What is a clear thermal bridge example in modern construction?
A common thermal bridge example is a metal through-wall flashing detail. Because metal conducts heat rapidly, it pulls heat directly through the building’s exterior insulation layer, acting just like a physical gap in the thermal envelope.
Why is a standard metal flashing detail problematic for energy efficiency?
A standard metal flashing detail creates a continuous thermal bridge along the exterior of a building. The metal conducts heat easily, bypassing the exterior insulation and causing significant energy loss, which dramatically increases heating and cooling demands.
Why is the metal flashing example considered the most overlooked issue?
Builders often focus heavily on mitigating minor thermal bridging from wood framing but ignore metal flashing. A metal flashing example is critical because a single project can contain thousands of linear feet of this highly conductive material, causing massive, unmodeled energy loss.
How does a poor thermal bridging detail cause mold?
A thermal bridging detail allows heat to escape, making adjacent interior wall surfaces extremely cold. When warm, humid indoor air meets these cold interior surfaces, condensation forms. This trapped moisture eventually leads to toxic mold growth and structural rot.
What is continuous insulation flashing?
Continuous insulation flashing involves using non-conductive materials—such as specialized membranes, rigid plastics, or fiberglass—to provide water drainage without breaking the building’s thermal envelope.
How does exterior insulation flashing improve building performance?
By using non-metal exterior insulation flashing, project teams ensure that water drains safely away from the wall assembly without creating a highly conductive thermal bridge. This preserves the building’s energy efficiency and prevents the dreaded performance gap.
This is one of those cases where the label performance should not be taken at face value: U-value of glass units – if the glass is meant to be installed horizontal or with a tilt angle. The analysis shown here illustrates the performance of two different IGUs, depending on the tilt angle.
Thermal performance of insulated glass units (IGUs) is driven by the combination of 1) the number of gas pockets (or in layman’s terms, the number of glass panes), the thickness and the fill of the glass pockets, and the low-emissivity coatings (low-e) on the glass panes).
The gas pockets provide insulation because the gas (whether air, Argon, or Krypton) conducts less heat than a solid. The more still the gas remains, the higher its insulation property, the lower the heat losses.
However, the gas does move. In doing so, it is subject to gravity, meaning that its ability to provide insulation is impacted by the tilt angle of the IGU.
Unfortunately, manufacturers provide glass U-values assuming the glass is vertical, even for IGUs intended to be installed horizontally or at an angle – as in the case of skylights. In other words, the label value may not represent the actual performance of the glass.
The performance gap is not negligible – the heat losses through the glass can be up to 30-35% higher than the label value.
Of course, this does impact the risk for condensation, as well as the whole building energy performance.
I-Joist vs Larsen Truss:
Does it make a difference for exterior high R-Value insulating?
Many high-performance buildings, when addressing the issue of super-insulation, will opt for traditional 2×6 stud framing with an added layer of exterior insulation to help reach the higher R-Values. One affordable and popular way to do that is with dense-packed, blown-in cellulose or fiberglass.
When considering the framing options for that exterior cavity, many builders will be inclined to use I-Joists and assume that any thermal bridging caused by that type of framing is negligible.
The thing is… the higher the performance, the more these seemingly small details can result in a gap between the expectation and the result.
Enter the Larsen truss option. A Larsen truss, with its point-to-point gussets (the small strips of plywood that connects the inside chord to the outside chord of the truss), greatly reduces the effect of thermal bridging compared to the continuous web of an I-Joist.
Our graph pictured here shows percentage, but you can think about it in dollars for effect. For every $100 you spend on a nominal R-Value, the Larsen truss gives you $92.50 of performance, while the I-Joist only delivers $81.10. So you basically lose about 10% of your expected R-Value.
The higher your goal, the more educated you need to be in making decisions like this. You may still decide to go for the I-Joist, for labor reasons or otherwise, but it’s important to arrive there as a well-informed decision. Every element of good design/build is an evaluation of trade-offs.
Go forth. Learn. Make informed decisions. And #RunWildBuildPassive !
In this article, we cover two very important aspects of glazings: light transmission and the solar heat gain coefficient.
These parameters are extremely important for performing buildings and passive houses, however, they are often overlooked by both designers and window manufacturers.
We’re going to describe how silly it is to evaluate the quality of a window or a door by its average Uw value alone, even if it is calculated according to ISO 10077-2. About ISO 15099, we reserve judgment until we gain more confidence with the norm.
Thinking of window quality through its Uw value is as silly as saying that a zebra is a “light grey” or “dark grey” horse: it does not make sense.
If you think that a zebra is a grey horse, then the Uw value is all you need.
A mediocre window may look to be performing well, due to a very low transmittance value of glass, Ug, regardless of the fact that you may have condensation (or ice!) forming along the edge of the glass.
Ice forming along the edge of the glass, on the room side, due to very low window quality.Window in a passive house near Riga, Latvia.
THE VALUE OF A WINDOW
What’s the purpose of an opening? In a building, windows and doors:
connect the inside to the outside;
contribute to the overall aesthetic of the building;
create views;
allow for natural ventilation;
provide daylight to the interior environment.
Palazzo Rucellai in Firenze, designed by Leon Battista Alberti. Doors and windows have always played a fundamental role in the aesthetic composition of architecture.
The aesthetic value of openings in a building is undeniable.
Daylight requirement and energy performance of glass units may be in contrast with one another. To lower the thermal transmittance of glass, Ug, insulated glass units (IGUs) are created with double or triple glass panes, with low-e coatings (made of metal oxides).
With the same type of glass, the more the number of panes, the less light gets through. Choosing the type of glass (e.g. extra clear glass), can have a very important effect on the quality of the internal environment, in terms of daylight.
As far as low-e coating, if their quality is not excellent (standard coatings), a low thermal transmittance Ug is associated with a low light transmittance.
In order to conciliate low thermal transmittance and high light transmittance, the low-e coatings need to be “selective”. They need to be able to reflect the infrared component of the spectrum and transmit the visible light. This is why a proper specification of a glass unit includes the light transmission value (to be 70% or higher), besides the thermal transmittance Ug.
We’re going to publish an article on daylight, and how this is affected by the type of IGU (double pane vs triple pane; standard low-e vs selective).
SOLAR HEAT GAINS
Solar heat gains represent the portion of total solar radiation (visible light + infrared), that is transmitted through a structure, and penetrates into the building. For insulated opaque assemblies (walls, roof, etc.), the amount of transmitted solar radiation is negligible; for glazed elements, it is extremely important.
The term “passive” itself derives from the fact that a passive house is such an efficient thermal envelope, that the solar heat gains become a determining factor (as well as the interior heat gains).
The solar factor g, also called SHG (solar heat gains) represents the amount of total solar radiation transmitted by the IGU – it is expressed as a percentage, or as a number (from 1,00 to 0,00). As in the case of the thermal transmittance of glass, Ug, the solar factor g also has to be expressed with two decimal figures.
In a well-designed building, the openings can become the most cost-effective “solar panels”, and provide “free gasoline” (solar gains), to keep the building comfortable in winter and reduce the demand of energy for heating.
The solar factor g represents the amount of “free gasoline” provided by the windows to the building.
Let’s get used to seeing the solar factor g as “free gasoline”, provided by the glazed components of the thermal envelope (Image source: TurboSquid)
The solar factor g is a very important element in the energy design of the entire building, next to the thermal transmittance of the glass, Ug, and the light transmission.
The question a designer needs to ask is: does the building need solar gains?
In residential building, even in moderately warm climates (e.g. Northern Italy): probably yes;
In non-residential buildings, with high interior heat gains (high number of people, appliances, etc.): maybe no.
The solar factor has to be designed as an integral part of the thermal envelope so that its effect can be evaluated for both winter and summer.
OVERHEATING
Let’s remember that any unshaded glass (even single pane), can cause overheating: the cause of that does not lie in the thermal performance of the glass per se, but in poor design or use of the building.
A car parked in the sun. This is equal to an uninsulated building, provided with single pane glazings. Overheating is caused by human error (poor design, poor management, or both), not by the energy performance of the building or of the glass.
To avoid overheating and guarantee daylight, the best strategy is to provide the building with external adjustable shading devices. This allows building users to manage daylight and solar gains based on season and daily activity schedule.
A building without shading is like a car without brakes: if you lose control (if it overheats), it is not the fault of the accelerator.
If solar gains need to be constantly kept low (e.g. non-residential buildings, with high interior heat gains), the glass units can be provided with a low solar factor on purpose.
GOOD GLASS, BAD GLASS
Let’s have a look at a data sheet we received from a window manufacturer for a residential project near Reggio Emilia, Italy.
In the eyes of the manufacturer, the glass unit was extremely good, with a Ug value of 0,47 W/m2K (0,08 BTU/h*ft2* °F, about R12). In his mind, this would have allowed his 92 mm solid timber frame window to meet passive house requirements in the local climate (which is not true, because he was considering the bare Uw value, without installation thermal bridges).
The data sheet of the glass. Top left: the widow manufacturer highlighted in green the Ug value, which made him think that the IGU could be very performing.
If you keep in mind what described above, it is evident how this glass unit is really not very good, because is provided with low-quality low-e coatings, not selective ones.
A light transmission of 50% would probably cause the failure of the windows to provide the minimum daylight factor (2%), with electrical lighting being required during daytime.
On the other hand, a solar factor of 0,30 (30%) dramatically reduces the overall energy performance of the building, and increased the demand for heating, even if the thermal transmittance Ug is better than other glazings.
Is this a “bad” glass?
Glazings are very dynamic components of the thermal envelope. In order to understand if a glass unit is appropriate for a specific building, in the local climate, you need to carry out an analysis on the entire thermal envelope. This cannot be done by the window manufacturer: it needs to be done by the designer of the building.
CONCLUSIONS
Glazed openings provide a determining contribution to the energy balance of high-performing buildings and passive houses.
The selection of insulated glass units has to be made based on climate, urban context, and use of the building. Thermal transmittance of glass, Ug, has to be paired with light transmission and solar factor g.
The quality of glass has consequences on the overall quality of the building, in terms of comfort, daylight and energy efficiency. For this reason, the design of the glass units has to be carried out by the designer of the building, not by the window manufacturer.
