Queen of Zero: Lessons Learned

In a story of rebirth, a 1901 Queen Anne Victorian–style house that was destroyed by a tragic fire has become the Queen of Zero—a phoenix of a house rising from the ashes with its architecture true to the original’s turn-of-the-century aesthetic but its performance aligned with the U.S. Department of Energy’s Zero Energy Ready Home (ZERH) standard.

The site is located in a historical district of suburban Maryland just outside Washington, D.C. Though the area was once full of stately Victorians, the stock of these centenarian balloon-framed antiques has dwindled significantly. The neighborhood is now predominantly a mix of mid-century bungalows and newer, production-built craftsman-style houses.

Queen of Zero’s owner, a longtime Maryland resident with a deep appreciation for historical preservation, explained that after the fire, “it was never a question of whether we would rebuild” the original home. Yet, recognizing the demands of a changing climate and rising utility costs, the owner sought to modernize the functional aspects of his new home with advancements in energy efficiency, resiliency, and comfort. To achieve net-zero performance, Queen of Zero incorporated a host of innovative products and materials, such as solar shingles and an exterior shell made of structural insulated panels (SIPs).

As the CEO of Symbi Homes, a greenbuild developer and consulting service, I have worked for more than a decade at the forefront of high-performance homebuilding, seeking to forge new pathways for sustainability in residential construction. At the Queen of Zero project, I served as director of sustainability, working to ensure that the project aligned with our zero-energy goals, while maintaining the integrity of its Victorian aesthetic.

I worked alongside an all-star team of veteran sustainable-homebuilding professionals including architect Michael Romero, Matt Kulp and Keyur Shah of Daks Builders, Kelly Gillespie of Kelly Green Energy Raters, and Daniel Santaella of Unik Creative Studio.

The home was completed in about 13 months, achieving everything we set out to do and then some, as the project evolved over time both at the homeowner’s direction and as a result of our net-zero requirements. In this article, I highlight many of the unique and challenging aspects of this build, discussing lessons learned along the way. The article concludes with my reflections on how this case study can inform a larger effort for advancing high-performance homebuilding.

What Is ZERH?

Launched in 2012, the U.S. Department of Energy’s Zero Energy Ready Home (ZERH) certification program provides standards for the design and construction of single-family and multifamily properties that achieve a level of performance whereby the home’s energy consumption could be offset almost entirely by renewable sources. In addition to the exceptional level of energy efficiency they promote, ZERH standards boost the durability and resiliency of buildings, while lowering maintenance costs and increasing occupant comfort and well-being.

I think of ZERH as the Energy Star program “on steroids.” To meet the ZERH standard, a home must comply with the requirements for Energy Star Version 3.1, EPA Indoor AirPlus, EPA WaterSense, EPA Renewable Energy Ready Home, and the Energy Star Water Management Checklist. And that’s just the beginning!

ZERH homes are designed to achieve a HERS (Home Energy Rating System) score of 50 or less, which is at least 50% more efficient than a standard reference home, and about 25% more efficient than the average Energy Star–certified home. The Queen achieved a HERS score of 15 when modeled with the 12.3kW solar roof capacity. The Queen’s HERS model estimates utility cost savings of about $6,000 per year compared with a conventionally built reference home (equivalent to the 2006 IECC).

ZERH Implementation

Achieving ZERH certification requires assembling a team of high-performance-homebuilding experts and gathering their input early in the project’s preconstruction design phase. Team members include a third-party green rater with the credentials for certifying ZERH homes who can review architectural drawings for program compliance. In addition, the HVAC contractor and/or mechanical engineer should be engaged early to begin modeling the mechanical systems via the ACCA Manual J, D and S. The builder also needs to complete the Department of Energy’s ZERH training and registration process.

During construction, the green rater will want to stay updated on the progress at each stage of construction. Although ZERH requires only two on-site inspections (pre-drywall and final), there are several requirements that will need to be verified via photo documentation. For this reason, I recommend creating a shared drive of construction progress photos accessible to the green rater in real time.

A Victorian ZERH

Traditional Victorians are fanciful and embellished—reflective of a moment in history when homes served as artistic expressions and status symbols made possible by the invention of power tools and a growing middle class during the Industrial Revolution. This architectural vernacular of elaborate trim details and intricate brass fixtures may seem at odds with the concept of a newly built net-zero home, which often conjures the image of a minimalist contemporary house or off-grid cabin.

However, from a theoretical perspective, the high-performance features of a net-zero build exist primarily outside the realm of embellishments, focusing on the mechanicals, wall systems, windows, insulation, and air-sealing (the “guts” of the home). For this reason, much of the Queen of Zero project followed a typical playbook for constructing a ZERH-certified home, with some exceptions when the aesthetics and performance seemed to duel. For example:

Rooftop renewables. The complicated roof structure with its many pitches, hips, and valleys meant that installing solar panels would be virtually impossible and practically useless, especially considering the county’s setback requirements. Thus, the decision was made to source a Tesla Solar Roof with the added bonus of the material’s low-tech look resembling historical slate shingles. The Tesla solar installers recommended a naturally vented roof, which proved challenging due to the complicated roof design and the fully unvented third-floor attic space. To solve for this, the team opted to install the roof sheathing on 1-by purlins, holding these a couple of inches back from the hip and valley rafters to provide a channel for air to flow past the purlins at these locations.

Air-sealing and insulation details. To be sure, a nice, flat, continuous wall is much easier to air-seal and insulate than one with a variety of projections, curves, or funky angles. Yet, Victorians favor dormers and bay windows, which are notoriously leaky. And the rafters of a turret roof contain dozens of nonperpendicular angles. With each architectural detail in the Queen’s structure, our crew had to pay particular attention to how these spaces would be properly insulated and air-sealed, using a variety of products (spray foam, cellulose, caulk, rigid insulation, etc.) to get the job done.

Low-emission finishes. The tighter the home, the more critical it is to avoid adding materials that emit indoor air pollutants such as VOCs. However, when it comes to wood finishes, low-emission products are typically lighter in color and sometimes difficult to apply. The hardwood flooring installers refused to use a water-based product, for example, because of the challenges in covering a large room without areas of patchiness or uneven finish. Fortunately, we found a great product—ProCoat UnoCoat Hardwax Uroil, a no-VOC stain that provides consistent coverage in a variety of dark, rich colors that perfectly matched the wood trim.

LED lighting. ZERH homes reduce energy costs in part by requiring LED bulbs in all lighting fixtures. When the design calls for period lighting (as in, the period when electricity was invented), LED fixtures can be scarce, but many antiques can be retrofitted with LED bulbs that mimic the original look. At the Queen of Zero, the homeowner purchased several decorative antique lights that were expertly and beautifully retrofitted for efficiency.

Cozy fireplaces. Ideally, a well-sealed ZERH home would not include any combustible gas appliances or equipment that might introduce toxins into the indoor air. Victorians are known for their multiple fireplaces with decadent mantels and hearths, cherished family gathering spots. I asked the homeowner to consider a variety of electrical inserts—typically LED-glowing fake logs with a background video playing flickering flames—for the home’s two prominent fireplaces. He understandably turned me down and instead opted for direct-vent gas inserts with fixed, flush glass fronts.

Mechanicals Fit for a Queen

Designing an optimal heating, cooling and ventilation system for the Queen of Zero was no easy feat, especially considering its location in Maryland (zone 4A), a mixed climate with high humidity levels. Our team of mechanical experts needed to address both comfort and efficiency in a tight home conditioning all four floors with a segmented layout typical of Victorians.

Now that the home is near completion and the system is operational, I can attest to the superior level of comfort (thus far) throughout all four levels of this 4,800-square-foot home. In September with outdoor temps near 80°F and humidity an average 74%, the Queen’s interior achieved a consistent 72° and 45% humidity, even in the finished attic space on the third floor. Most notably, the home stayed relatively comfortable during workdays when a constant stream of crew members entered and exited the property’s seven exterior doors.

System components. The Queen of Zero is heated and cooled via four high-performance cold-climate heat pumps manufactured by Mitsubishi Electric HVAC US. With the exception of the basement music room, the house is conditioned via three ducted air handlers serving 1) first floor and partial basement; 2) second floor; and 3) third-floor finished attic. The basement music room, built with extensive sound-attenuation materials in the walls and ceiling, has a dedicated wall-mounted mini-split for heating and cooling—a ductless system designed to reduce sound-wave transmission to adjacent areas of the home.

At the jobsite, we have a saying, “This is not your grandmother’s Victorian,” and the final mechanical design is a perfect example. Despite the home’s conventional turn-of-the-century layout with its many segmented rooms and despite the central staircase that encourages the stack effect of warm air rising to the upper floors, the compartmentalization of the Queen’s HVAC into four distinct systems, each with its own thermostat and controls, ensures optimal comfort in all areas of the home. Gone are the days of sweltering attic spaces and chilly, damp basements.

As per ASHRAE 62.2 ventilation standards, the tight envelope of this high-performance home (less than 2.0 ACH50) requires a whole-house mechanical system to help circulate fresh air. We selected an AprilAire V22BEC Energy Recovery Ventilator (ERV), which transfers much of the energy used to heat or cool the indoor air from the exhaust air to the intake stream as it dumps fresh, filtered air into the supply side of the Mitsubishi Electric SVZ-KP24NA air handler. The V22BEC ERV also pairs with AprilAire’s 8120X Ventilation Controller, which monitors outdoor temperatures and will adjust its schedule to avoid bringing in fresh air during the hottest, most humid times of day.

To control humidity in the house, we added an AprilAire whole-home dehumidifier to each heating and cooling system. Importantly, these units can monitor indoor humidity levels and operate independently from heating and cooling demands. In other words, even in conditions where the thermostat is not calling for cooling, the dehumidifiers will run to remove excess humidity from the conditioned space. Similarly, a whole-home AprilAire 800 Steam Humidifier connected to the first-floor air handler will add humidity to the home during dry winter months—even when the thermostats are not calling for heat.

Addressing Duct Leakage

The ZERH program follows Energy Star standards for maximum allowable duct leakage. For this project, duct testing measurements could not exceed 6% air leakage (≤6 CFM25 per 100 square feet of conditioned space). Increasingly, local municipalities are also requiring duct tests to pass final residential building inspections. The requirement makes a lot of sense—leaky ducts reduce thermal comfort, decrease the efficiency of mechanical systems, and increase the cost of utility bills. Such rigorous duct leakage testing is a significant shift in the work processes for many residential HVAC professionals, who may not be accustomed to such scrutiny. I have yet to find a system that passes on the first manometer reading.

Retrotec’s Noah Lawrence assisted with pre-drywall duct testing. His initial tests did not go as planned—results showed approximately 12% duct leakage, which is double the allowable amount for ZERH certification, on all three ducted systems. We worked with the HVAC contractors over several days chasing theatrical-smoke trails to find and plug the leaks before we finally managed to get the duct leakage below 6% at pre-drywall. One lesson learned: We should have tested the attic systems prior to spray-foam installation, as it was difficult to reach some leaks in the tight cavities behind the knee walls.

Because this process of sealing the ducts can be labor-intensive, it is important to include the standard for maximum allowable duct leakage in the HVAC subcontract so expectations are clear up front. Also, it helps to clarify who will be responsible for additional consulting fees if the green rater needs to make multiple trips for testing and diagnostics.

Humidity Control

High-performance building standards tighten and fortify a house’s exterior shell to keep the outdoor elements at bay, while maintaining more consistent, comfortable conditions within the house. In theory, this beefing up of the shell means that the mechanical systems will work less to heat and cool the indoor space. However, in many climates, less conditioning and less natural airflow will necessitate whole-home humidity control mechanisms that operate independently from heating and cooling equipment.

Over the years, I have learned that a standard Energy Recovery Ventilator (ERV) does not provide adequate dehumidification of indoor air in our humid climate zone. In fact, even though ERVs remove some of the humidity from the incoming ventilation air, they do not remove all of it and can still make indoor humidity levels rise on days when the outdoor environment is particularly moist. For this reason, we installed an ERV at Queen of Zero that includes an outdoor climate sensor to limit the ventilation intake when outdoor relative humidity levels rise.

In addition, it is important to note that adding a dehumidifier in the basement, the most common location for homes in our area, would not be sufficient for this project. According to Doug Horgan, vice president of best practices at BOWA, a Washington, D.C.–area custom home-building and remodeling firm, “Humid air is lighter than dry air. So everything else being equal, if your house is closed, your upper levels will end up with more humidity.” In other words, a dehumidifier in the basement will do nothing to solve humidity problems on the upper floors of the home, which is why the Queen of Zero has a ducted, whole-home dehumidifier attached to each heating and cooling system.

Horgan also points out that dehumidifying equipment inherently adds heat to the treated air and therefore recommends that ducted units operate on the supply side of the air handler. At the Queen, the HVAC contractor, Ridgchi Appadoo, found that the warm air emitted from the dehumidifiers was causing the Mitsubishi Electric air handlers to operate less efficiently. The solution was to alter the settings on the AprilAire equipment to reduce its operation slightly—more specifically, the dehumidifier was programmed to operate only when the thermostat was not calling for cooling.

Equipment integration

In total, 14 pieces of mechanical equipment regulate the Queen’s indoor air and operate in harmony to ensure optimal comfort for her occupants. To help manage the system from a user perspective, Appadoo opted for Ecobee Premium Pro Wi-Fi-enabled thermostats, which allow the homeowner to control the complex system from one app on his cellphone.

However, because there are some limitations of the Ecobee thermostats pairing with Mitsubishi Electric air handlers, Appadoo used an Airzone Aidoo Pro module to integrate the Mitsubishi system with the Ecobee Premium Pro thermostats and AprilAire dehumidifiers. According to Appadoo, “This setup allows all parts to work together seamlessly, providing optimal temperature and humidity control tailored to the home’s needs.”

Tweaks to the System

Despite our concerted efforts to model the mechanical loads and duct design, the system has still required some adjustment. For example, we found that the system sometimes struggled to keep up with afternoon solar heat gain in the kitchen from a 2-by-4‑foot skylight. Fortunately, the homeowner had the foresight to purchase a solar shade with his Velux FCM 2246 skylight, which solves this problem.

We anticipate adjustments to the system will continue through four seasons of occupancy. Joseph Hillenmeyer, AprilAire senior product manager, explains that many factors can impact how mechanicals function—from number of occupants, to opening windows, to cooking and showering habits. “As people live in the house, they probably will end up tweaking the equipment to an extent. But if you don’t include [the equipment] on the front end, then they’re calling someone to [install] it later, and it’s always going [to] be more difficult to retrofit those things. At least now we know everything’s designed for the size of the house and the operation of the house, and the tweaks they want to make will all be possible.”

Another significant factor impacting performance will be equipment maintenance. The Queen’s HVAC system has at least 11 air filters throughout the house that will require regular cleaning or changing, with schedules varying based on manufacturer specifications, filter type, and degree of use. The upside to all this housekeeping is incredibly pristine indoor air, as the filters are designed to remove a plethora of airborne toxins and pollutants such as dust, mold, and viruses.

Of course, none of this innovative work would be possible without a highly competent and dedicated team of HVAC professionals willing to go above and beyond business-as-usual. Appadoo and his staff at Thermal Plus participate in advanced training and professional development opportunities as an integral part of their business model, which means they are uniquely prepared for increasingly stringent building energy codes on the horizon. Our team has also benefited from direct communication with the manufacturers, which offered valuable advice and technical assistance throughout the project.

Scaling Sustainability

In conclusion, I turn to a question posed at the outset of this case study: What do our lessons learned from Queen of Zero teach us about scaling sustainable homebuilding across the country? Less than 1% of all homes built in the U.S. achieve the Zero Energy Ready Home standard. What will it take to increase that number to even 5% or 10%? What barriers exist to more widespread adoption of high-performance homebuilding practices?

The Queen of Zero case study demonstrates that it is possible to build to a higher standard of performance while also tackling the complexity of an embellished architectural vernacular. Net-zero homes do not need to look like square boxes. Given a generous budget, performance and Victorian aesthetics can coexist.

I have also built ZERH homes without a generous budget. I have found that the efficiency upgrades of a net-zero build may add 5% to 10% to the construction costs but that those expenses can be offset by value engineering other parts of the project. Budgets aside, there are some significant gaps that I believe need to be addressed to scale sustainable homebuilding in the U.S., including:

The workforce gap. Although the project benefited from a leadership team experienced in building sustainable homes, the vast majority of crew members were learning on the job how to adapt to high-performance standards. The first framing crew, unfamiliar with how to install SIPs, complained that site supervisor Matt Kulp was being “too picky” and walked off the job after their first day. Thus, builders should be prepared for some growing pains as they work to assemble a competent and willing team, one that may have had a limited history of training opportunities. The challenge is not only to fill gaps in knowledge but also to encourage a growth mindset that welcomes the learning process.

The incentive gap. Building to a net-zero standard requires more planning time, a longer production calendar, and more resources for project management and oversight than building a similar conventional, code-built home. At the Queen of Zero, we had five conference calls to finalize the design of the naturally ventilated roof—just one detail out of many that required special care and attention. Builders who complete a for-sale ZERH-certified project are eligible for the 45L federal tax credit up to $5,000. Homeowners who build a ZERH are eligible for additional federal tax credits (for example, the renewable energy tax credit) through the Inflation Reduction Act. These benefits are helpful, but I don’t believe they’re sufficient to encourage more widespread adoption of the program. The trades, for example, should also be incentivized to stretch their knowledge and techniques to adapt to the standards.

The ecosystem gap. It’s one thing to specify a bunch of “high performance” equipment and materials, and quite another to expertly assemble all the components of a house into one integrated system that optimizes comfort, resiliency, and efficiency. This ecosystem approach requires that the design and construction of the house considers the climate, inhabitants, and uses of the property. A well-balanced ecosystem incorporates the underlying principles of building science and can adapt to a changing environment. Collaboration is key, and all contributors must be on board with the sustainability program.

The testing gap. High-performance houses are subjected to more rigorous testing and inspections than typical builds. A ZERH house has a required pre-drywall inspection that includes duct testing for air leakage and a detailed quality check for insulation installation. At Queen of Zero, we added a pre-drywall blower door test to identify any unplugged exterior penetrations. In my experience, many of these pre-drywall energy inspections happen after the county’s building official has already inspected and approved the project for close-in. Yet, the little gaps and cracks identified by energy auditors at pre-drywall can have a tremendous impact on the performance of the house.

In the pursuit of building better houses, working to fill these gaps and make the leap to high-performance homebuilding may seem overwhelming or otherwise unattainable. Yet, at the moment I am writing this conclusion, I am also wrapping up participation in a local workgroup gathering industry input on code changes for residential construction in the District of Columbia. Similar to other jurisdictions around the country, D.C. will soon be requiring net-zero standards for all new homes and substantial renovations. It’s hard to believe but, in the coming years, building homes that produce as much energy as they consume will likely become the norm, not the exception.