Putting Building Science into Practice: Inside Allison Bailes’ Retrofit

When it comes to building science, few names carry as much weight as Allison Bailes III, PhD, founder of Energy Vanguard and author of A House Needs to Breathe…Or Does It?. He is one of the most widely read educators in the building performance industry. Through his business, his book, his training courses, and his influential blog, Bailes has spent decades helping contractors, designers, and homeowners understand how buildings really work and why good science must guide good practice.

Recently, he has put theory into practice in the most personal way: by retrofitting his own 1961 home in Atlanta, Georgia. The project has given him an opportunity to test a range of innovative products firsthand, from basement insulation panels to heat pumps and indoor air quality monitors. In a recent conversation, Bailes shared his experiences, lessons learned, and perspective on which products are pushing the field forward.

Choosing Innovation Carefully

When asked how he decides whether a product is worth using in his own home, Bailes was quick to point to first principles. “The first thing is, it’s got to be compatible with what I know about building science,” he said. “You want the product to make sense for the goal. It has to be right for the climate and right for the building.” That means climate matters, application matters, and installation details matter.

That approach guided his choices in the basement—a space common in Atlanta’s hilly terrain, though not always treated with the care it deserves.

Insulating with InSoFast Panels

One of the most intriguing products Bailes used is InSoFast, a continuous insulation panel system designed specifically for basement walls and floors. The panels are made of expanded polystyrene (EPS) foam with embedded polypropylene studs. The back of each panel features dovetail grooves that accept adhesive for mounting directly to concrete or block walls, while the front provides integrated studs for fastening drywall.

The panels bring multiple benefits in one product: insulation, an attachment surface, and a
strategy for reducing thermal bridging. “It’s not just foam,” Bailes explained. “The panels have
plastic studs embedded, and they’ve been tested to hold a lot of weight. Once I figured out the
installation process, it went pretty quickly.” By sealing tightly to the walls and floors, they also
help reduce the movement of soil gases—an essential factor in a house like Bailes’, which has
elevated radon levels.

Still, the product has its limits. The thickness of InSoFast panels (2 and 2.5 inches in Bailes’
home) can complicate floor applications, particularly where stair transitions are involved. “If I
had put it on the slab in the part of the basement where the stairs are, I would have had to
reframe the stairs, which wasn’t practical,” Bailes said. He opted to use it only on the walkout
portion of the basement floor.

There was also a performance trade-off to consider. Leaving the concrete slab uninsulated in certain areas maintains the concrete’s thermal mass, which can be beneficial for resilience. “An uninsulated slab will absorb heat during the year and slowly release it back,” Bailes noted, pointing to modeling that shows how this can stabilize indoor temperatures in both winter and summer and help keep pipes from freezing during outages.

Despite the challenges, Bailes is enthusiastic about InSoFast. “It worked great. It’s easy to work with. If you have fairly flat walls made from poured concrete or CMUs [concrete masonry units], then I think it’s a good product to use.”

Heat Pumps: Real Solutions

For heating and cooling, Bailes relies on inverter-driven mini-splits. His home includes three
outdoor units connected to five indoor units, a mix of ducted and ductless air handlers.

“The heat pump decision was easy,” he said. “Mitsubishi makes great equipment, and we already
use it in our office. We do HVAC design all over the country, and a high percentage of the jobs
we do specify Mitsubishi equipment, so we’re very familiar with it.”

Other manufacturers, such as Daikin, Fujitsu, and LG, also make high-quality variable-speed
systems, but Mitsubishi’s extensive support network gives it an edge, especially for homeowners.
“It’s easier to find contractors who know the equipment, and parts are more readily available,”
Bailes noted. “Other manufacturers are working on improving in those areas.”

Tracking Indoor Air Quality in Real Time

Indoor air quality (IAQ) has become a growing priority for Bailes, both professionally and
personally. He recently developed an online course on IAQ through HeatSpring and is preparing
follow-up classes on filtration and ventilation. At home, he relies on affordable consumer-grade
monitors to keep tabs on conditions.

“I have two Awair Element monitors,” he explained. “They give you temperature, relative humidity, carbon dioxide, particulates (PM2.5 [particulate matter smaller than 2.5 microns]), and VOCs [volatile organic compounds]. I almost never look at the overall score; I focus on the individual readings.”

He also uses two different monitors from Airthings, one of which measures radon, an especially important factor in his area. Atlanta lies within an EPA-designated Radon Zone 1, where average indoor levels are 4.0 picocuries per liter (pCi/L) or higher. Elevated radon is common in Atlanta homes with basements, and Bailes’s monitoring has confirmed higher levels in his home.

“We have high radon in our house,” Bailes explained. “The basement remodel reduced it, but it’s still high enough that I’ll need active mitigation. The monitor helps me track progress.” Active radon mitigation systems typically use a sub-slab depressurization fan and vent piping to draw radon gas from beneath the foundation and safely exhaust it outdoors—a straightforward but highly effective approach for reducing exposure.

Bailes is practical about the limitations of these devices. “They’re not research-grade instruments. There’s some inaccuracy, but they’re good enough to tell you when something’s going on. And the apps make it easy: graphs show green, yellow, or red zones, so even a homeowner who doesn’t know the exact thresholds can understand when there’s a problem.”

The air quality monitors have provided useful lessons like the time a burnt grilled cheese sandwich triggered a noticeable spike in particulate matter. And, more seriously, when demolition work in the basement involving a gasoline-powered concrete saw caused PM2.5 levels six times higher than the cooking mishap. “That was not a good day,” Bailes recalled. “The workers didn’t have proper protection, and it showed how critical IAQ awareness is during construction.”

Spray Foam in the Attic

In the attic, Bailes chose to work with a spray foam product supplied by Enverge Spray Foam, a partially bio-based insulation that incorporates sugarcane waste. Installed by a local contractor, the open-cell spray foam helps control heat and humidity in Atlanta’s humid climate.

“It went well, and the attic is doing great,” he said. The decision was shaped not only by performance but by relationships—knowing trusted people in the industry and contractors capable of sound installation.

Hot Water Distribution: Small-Diameter PEX

Another upgrade focused on hot water delivery. In many older homes, oversized plumbing combined with low-flow fixtures results in prolonged wait times for hot water. In his 1961 house, Bailes often waited nearly three minutes for hot water to reach the kitchen sink.

The solution was a retrofit with small-diameter PEX [cross-linked polyethylene] piping and
manifolds. In this case, Bailes even fabricated his own copper manifolds to learn the art of
soldering. The result: much shorter delivery times, reduced water waste, and improved comfort.

Lessons on Innovation

Not every product is perfect for every home. For example, Bailes points out that InSoFast works
best on smooth, flat walls but not on rubble stone foundations. And consumer-grade IAQ
monitors cannot replace professional diagnostics, but they’re accurate enough to guide
homeowners toward healthier living conditions.

Still, the value of innovation lies in expanding options. “If you have the right conditions and the
right goals, products like these can really simplify the work,” he said.

When asked what he sees as underrated in the industry, Bailes pointed to two categories:
modular construction and air-to-water heat pumps. Modular homes, built in factory-controlled
environments, can achieve tighter tolerances and higher quality than traditional site-built
methods. By reducing weather delays and minimizing jobsite variability, modular construction
can deliver better insulation continuity, fewer air leaks, and less material waste. Many in the
building science community see this as a path to higher performance as energy codes tighten.

Air-to-water heat pumps, while still emerging in the U.S. market, offer an efficient alternative to
traditional HVAC. These systems move heat between the indoor and outdoor units using water rather than refrigerant alone, creating flexibility in how heating and cooling are distributed indoors. They can work with radiant or other hydronic systems, or use fan coils for air distribution. This versatility makes them especially effective in retrofits where existing hydronic components are already in place.

A Retrofit That Teaches

For Bailes, retrofitting his own home has been as much about learning as improving comfort and
efficiency. It has given him an opportunity to experience products firsthand, confirm building
science principles, and test solutions he writes about in his blog.

In the process, he continues to share insights that guide others, whether it’s a contractor weighing insulation options, a homeowner curious about IAQ monitors, or an industry peer exploring the future of heat pumps.

Ultimately, the message is clear: Innovation matters, but it must always be grounded in building science. That combination of curiosity and rigor has defined Allison Bailes’ career, and it’s on full display in his ongoing home retrofit.