When Sunshine Mathon set out to remodel the Willowbrook House, he didn’t just aim for a beautiful, functional home—he wanted to prove that Net Zero Energy was possible in Austin’s climate. The project, completed in 2014, became a model for resource-conscious design in the region.
This deep dive will explore every key decision, from passive cooling strategies to high-efficiency systems, that transformed a 1948-built home into one of the most energy-efficient residences in Texas.
1. Energy Efficiency: Reducing Demand Before Producing Energy
The first principle of Net Zero Energy design is reducing a building’s energy demand before adding renewables. Willowbrook House started with a highly inefficient structure—uninsulated concrete block walls, single-pane windows, and outdated HVAC systems. The remodel completely reversed that, creating a tight, high-performance building envelope.
Envelope Upgrades: Keeping Heat Out, Comfort In
- Exterior Insulation → Instead of insulating inside, R-18 rigid foam insulation was added to the outside of the concrete block walls, allowing the mass to help regulate interior temperatures.
- High-Performance Windows → Fiberglass-framed, double-pane windows with tailored Low-E coatings were installed based on orientation:
- South & West-facing windows: Low SHGC (0.18) coating to block solar heat gain.
- North & East-facing windows: Higher SHGC (0.24) coating to allow beneficial winter heat gain.
- Spray Foam Insulation in the Attic → 8 inches of open-cell spray foam (R-28) at the roofline sealed the attic and created conditioned storage space.
Smart HVAC & Ventilation: Right-Sizing for Efficiency
- High-SEER Heat Pump HVAC System → A variable-speed Carrier Infinity heat pump that adjusts capacity based on real-time demand, reducing energy use.
- Ducts Inside Conditioned Space → Rather than placing ducts in the hot attic, they were strategically routed within insulated areas to reduce energy loss.
- Energy Recovery Ventilator (ERV) → Instead of bringing in unconditioned outdoor air, the ERV pre-conditions fresh air by capturing energy from outgoing stale air, improving indoor air quality without excessive energy use.
2. Renewable Energy: Onsite Solar Power
Once energy demand was minimized, Willowbrook House could offset its usage with solar energy. The final system was designed to generate slightly more energy than the home consumed, ensuring true Net Zero performance.
Solar Power System
- Photovoltaic (PV) System: 4.5 kW solar array (18 x 250W panels) with microinverters.
- Solar Hot Water: Two solar thermal panels pre-heat an 80-gallon storage tank, reducing reliance on electric water heating.
Electricity Use Breakdown (Annual)
- Total Consumption: 5,310 kWh per year
- Energy Use Intensity: 8.59 kBTU/sf/yr
- Breakdown by Usage:
- Cooling: 1,628 kWh/year
- Plug Loads & Equipment: 3,167 kWh/year
- Lighting: 100 kWh/year
- Water Heating: 187 kWh/year
- Heating: 228 kWh/year
With this setup, solar generation matches energy consumption on an annual basis, making the home Net Zero Energy Certified.
3. Passive Design: Working With, Not Against, the Climate
Austin’s hot, humid climate means air conditioning is a necessity—but smart design reduces how much cooling is needed. Willowbrook House used passive strategies to cut down heat gain before relying on mechanical cooling.
Key Passive Strategies
- Orientation & Shading
- The house was positioned to maximize shade during peak summer months.
- Deep roof overhangs block high-angle summer sun while allowing winter light inside.
- Thermal Mass
- The original concrete block walls were leveraged for their ability to stabilize indoor temperatures—absorbing heat during the day and slowly releasing it at night.
- Ceiling Fans
- Efficient induction-motor ceiling fans allow for higher indoor temperatures without discomfort, reducing cooling demand.
- Strategic Window Placement
- Windows were positioned for cross-ventilation, allowing fresh air to replace hot, stale air when conditions allow.
4. Eliminating Fossil Fuels: All-Electric Home
For full ILFI Net Zero Energy certification, the home needed to eliminate fossil fuel use. Natural gas was removed, and all systems were converted to electric.
Gas-to-Electric Conversions
- Gas Cooktop → Induction Cooktop
- Gas Furnace → Electric Heat Pump
- Gas Water Heater → Solar Hot Water + Backup Electric Heating Element
This shift ensured that every watt of energy used in the home could be offset with renewable energy.
5. Resource Efficiency: Water, Materials, and Future Adaptability
The remodel went beyond just energy—it also focused on long-term sustainability through water conservation, waste reduction, and material reuse.
Water Efficiency
- Low-flow fixtures and ultra-efficient showerheads.
- Strategic rainwater management to prevent runoff and erosion.
- Native, drought-tolerant landscaping (xeriscaping) to eliminate irrigation needs.
Material Choices & Waste Reduction
- Reclaimed Wood Flooring → Salvaged pecan and longleaf pine from an old Waco warehouse.
- Hand-Crafted Steel Details → Custom metalwork provided functional design elements without waste.
- Minimal Construction Waste → Many materials were either repurposed or locally sourced.
6. The Bigger Picture: Lessons from Willowbrook
Willowbrook House proves that Net Zero Energy is not just for high-budget, high-tech homes—it’s achievable with thoughtful, regionally responsive design.
Key Takeaways
- Existing homes can achieve Net Zero Energy with the right approach.
- Passive design is essential—reducing the need for mechanical systems makes achieving Net Zero much easier.
- Material reuse and smart sourcing matter—sustainability extends beyond energy use to waste reduction and longevity.
- Eliminating fossil fuels is possible—an all-electric home paves the way for a clean energy future.
For Webber + Studio, this project reinforces a philosophy we’ve always believed in: buildings should work with their place, not against it. Whether it’s an adaptive reuse project or new construction, we can apply these same principles to create more resilient, self-sustaining architecture for Austin.