When Symbi Homes set out to transform a 1950s kit home in Kensington, Maryland — known as the Retro Rambler — the goal wasn’t just to modernize; it was to prove what’s possible with sustainable building technologies. 

Today, that same 73-year-old home feels like it’s been completely reborn. “It’s like flipping a switch,” says Nicole Tysvaer, CEO of Symbi Homes, a residential developer focused on homes that emphasize wellness, energy efficiency and technology. “Rooms that were once drafty now feel like they’re wrapped in a warm, protective blanket.”

With the addition of SANCTUARY® by Greenfiber, soundproofing and comfort have improved dramatically, with outdoor noises nearly eliminated. “The acoustics are so good now with the cellulose insulation,” Tysvaer adds. “You could easily host a little home concert, and it would sound incredible.”

Greenfiber cellulose insulation, a sustainable, high-performance solution, helped Symbi create a Net Zero Energy Ready home without sacrificing the charm and scale of its original postwar design.

Net Zero Energy Ready homes are optimized to generate as much energy as an average family consumes annually. To take energy efficiency to the next level, the home can be upgraded to Net Zero with built-in and ready-to-use solar panels installed on the rooftop. 

This renewable energy source provides sustainable, low-carbon energy by generating electricity from the sun, saving you money over time. Together with cellulose insulation, these features create a strong foundation for lasting sustainability and comfort.

Where Can You Find Greenfiber in the Retro Rambler?

• Exterior Walls (in the Addition): Spray-applied SANCTUARY cellulose provided a full cavity fill for consistent coverage and reduced air leaks. 
• Ceilings: Dense-packed SANCTUARY cellulose enhanced sound control between floors, improving acoustic comfort.
• Attic: Blow-in SANCTUARY cellulose to R-60 delivered exceptional thermal performance and energy efficiency.
• Vaulted Second-Floor Ceilings: A hybrid assembly combined 5" of closed-cell foam with 7" of dense-packed cellulose. The foam creates an air and vapor barrier, while the cellulose adds R-3.7 per inch and helps eliminate thermal bridging.

Watch this video to see how Greenfiber was installed in the Retro Rambler's spray-applied walls. 

Although the house is still under construction and energy data is not yet finalized, performance monitoring will track energy use over the first 12 months after completion. Early observations suggest that the tight envelope and high-performing insulation are setting the stage for significant energy savings.

Why Symbi Homes Chose Greenfiber Cellulose Insulation

Tysvaer selected Greenfiber cellulose because it supports the company’s sustainability principles while meeting the performance demands of a Net Zero Energy Ready remodel. From safety and sustainability to comfort and efficiency, the insulation checked every box. 

• Nontoxic and Safe for Installers: Unlike spray foam, which typically requires crews to avoid the area for 24–48 hours while off-gassing occurs, cellulose insulation allows workers to reenter immediately after installation, keeping the project safe and on schedule.
• Carbon Negative: Made of 85% post-consumer recycled paper, cellulose locks carbon into the home’s structure, reducing overall emissions.
• High Thermal and Acoustic Performance: Cellulose delivers a high R-value of up to 3.7 per inch, improving both energy efficiency and sound attenuation for quieter, more comfortable homes. Its dense, interlocking fibers fill cavities completely, reducing sound transmission through walls and floors and providing best-in-class acoustic performance verified in lab-tested assemblies.
• Fire Resistant and Durable: Greenfiber cellulose insulation has a Class 1/A fire rating and qualifies as a fire-blocking material, enhancing both safety and long-term durability.
• Low Waste: Installation produces virtually no waste, as any excess cellulose can be vacuumed and reused, making the process environmentally friendly from start to finish.

Note on Pest Protection: For projects where pest protection is a concern, Greenfiber also offers SANCTUARY® DEFENSE, an insulation product treated with an EPA-registered pesticide that helps protect insulation from pests. Learn more.

What is the Retro Rambler project?

Located in a family-friendly, walkable community just outside Washington, D.C., the Retro Rambler is a 1952 Gunnison kit home originally built during the postwar housing boom. Like many ranch-style homes of its time, it was designed to be affordable, durable and easy to mass-produce.

Rather than tear it down and build new, Symbi Homes chose to remodel the aging structure, preserving the neighborhood’s character while demonstrating how older homes can be retrofitted to modern sustainability standards. The result is both a showcase and a blueprint: a Net Zero Energy Ready remodel that proves energy efficiency doesn’t have to come at the cost of architectural charm.

Building on Greenfiber’s previous collaboration with Symbi Homes on the Queen of Zero project, this remodel exemplifies the company’s commitment to circular, high-performance design.

The project’s main efficiency goals focused on:

• Tightening the building envelope with advanced insulation and air-sealing techniques
• Replacing the outdated mechanical system with a modern all-electric setup
• Achieving DOE Efficient New Homes certification while prioritizing health, comfort and sustainability

See the full project at Symbi Homes: Retro Rambler

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Challenges of Remodeling for Net Zero

Retrofitting this older home required addressing challenges that many new builds do not face:

• Thin Exterior Walls: With only 2.5" of cavity space for insulation — compared with 5.5" in typical modern 2" × 6" framed walls — the thin walls made it more difficult to achieve high R-values.
• Old Foundation: Poorly installed siding led to water infiltration issues that had to be fixed before improving the envelope.
• Moisture Damage: Persistent dampness caused ant infestations and material breakdown within the existing structure.
• Low Insulation Baseline: The home’s original fiberglass batts provided an estimated R-6, far below modern energy efficiency standards.
• Small First-Floor Footprint: At just 800 square feet, expanding the space while maintaining a tight building envelope required careful planning to minimize air leaks and energy loss.

One of the most critical challenges was thermal bridging: points in the building envelope where heat can bypass insulation through structural elements such as studs or joists. In older homes, thermal bridges can be extensive, causing significant energy loss, uneven temperature and condensation issues that may lead to mold or rot. 

Achieving a modern, airtight envelope in a 73-year-old structure required careful planning to minimize thermal bridges and integrate advanced air-sealing techniques throughout walls, ceilings and rooflines.

Why Projects Like the Retro Rambler Matter

Both market trends and regulatory shifts are driving the move toward higher-performance, low-carbon homes. Cities such as Washington, D.C., are already introducing net-zero requirements for new construction, and as building codes continue to evolve, builders and remodelers who adopt greener materials now will be better positioned to stay competitive.

At the same time, homeowner demand for sustainable, healthy and energy-efficient homes continues to grow. According to Green Builder Media’s 2024 Energy Insights survey, consumers are increasingly prioritizing features that improve performance and reduce environmental impact. While high-performance windows remain the top energy-efficient upgrade, COGNITION Smart Data surveys show that upgraded insulation has steadily increased in importance among homebuyers from 2022 to 2024.  

Projects like the Retro Rambler illustrate how these trends come together. The remodel serves as a replicable blueprint for thousands of postwar homes — including ramblers, Craftsman bungalows and Sears kit houses — that could be remodeled to net-zero standards, proving that sustainability and efficiency can coexist with neighborhood character. 

Partner with Greenfiber on Your Next High-Performance Project

The Retro Rambler shows how thoughtful design and the right materials can make net-zero remodeling achievable. 

Learn how Greenfiber insulation can help your next high-performance remodel or new build achieve comfort, efficiency and sustainability.

Frequently Asked Questions

How is remodeling an older home to net zero different from building new?

Older homes come with constraints such as thin walls, outdated foundations and minimal insulation. Achieving net-zero status requires careful upgrades to the envelope, insulation and air sealing while balancing comfort and indoor air quality, which are challenges new builds don’t usually face. 

Can projects such as the Retro Rambler be replicated in other homes?

Yes. Symbi chose a rambler style because thousands of similar older homes could benefit from added insulation and air sealing to improve comfort, efficiency and resilience. According to Tysvaer, the key is a holistic approach that applies building science principles to ensure upgrades also support optimal indoor air quality.

How does Greenfiber cellulose contribute to green building certifications?

In the Retro Rambler, Greenfiber’s cellulose helped the project qualify for the DOE Efficient New Homes program. More broadly, cellulose insulation’s recycled content, carbon storage and high thermal performance also support certifications such as ENERGY STAR® and National Green Building Standard® by earning points in energy efficiency, materials and indoor air quality.