Designing a Net-Zero Remodel
This is a complex process with no blueprint to follow. Your family’s lifestyle needs must be built in, along with energy efficiency, proper orientation to the sun, sufficient energy production, all subject to budget. There are so many variables to consider in designing a net zero home that each time is unique. Perhaps this is why so few remodel projects attempt to reach net-zero – because it is difficult to find (1) examples in each neighborhood; (2) architects, builders, and subcontractors to guide projects; and (3) boilerplate roadmaps to guide net-zero projects.
Here are the steps that we followed in the design stage.
1) Find the right house. If you already live there, skip this step. If not, look for a home with a clear view of the sky, preferably with roof surfaces facing somewhere between South and West. Look also for one where you can shade high summer sun on the south elevations, but let low winter sun in to passively heat the home. Look for west and east elevations that are not naked to the sun. See the story of our house hunt here.
2) Do an energy audit. Find out the features already in the home, and the flaws. Test the leakage of the HVAC ducts and the living space.
3) Do a solar study. Find out the potential generation of a typical PV array in your area,
with your available roof surfaces. We used 4 kW as a start, with simple ratios possible to scale up or down from there.
4) Evaluate various labels for your project, such as Build it Green, LEED, HERS rated, Energy Star, Water Sense, Passivhaus that can help guide your decisions and market your home to potential buyers someday and help the community to understand what you’ve built.
5) Set your goal for the project. Net zero at any cost? Only systems with 10-year paybacks? Eliminate all Tier III and IV electric and gas usage? All-electric? Indoor air quality? Sustainable materials? Minimal water use? What will success look like when it’s built and operational?
6) Reconfigure the space to fit your family. Think about natural breezes, where the sun rises and sets, the natural environment that your house needs to embrace and coexist with most days of the year. Most of all, make it a comfortable set of spaces for your family that will adapt to your evolving needs over time. If we do this right, we won’t have to move every 7 years, which is the American average. This is the stage you may want to hire an architect to learn how your family lives, thoroughly research local ordinances, test different floor plans, and eventually produce the construction documents.
7) Model the performance of the building.
Energy modeling can be performed by many people, including architects, contractors, consultants, and engineers. Find someone with experience and the right software to take your building design and forecast its energy usage with multiple what-if scenarios to optimize performance-cost tradeoffs.
8) Build a budget: identify any incentives for your project, such as utility rebates, government tax breaks, and local city programs to make your project as affordable as possible. Get a ballpark quote from a general contractor for the general scope of work you are considering without any bells and whistles. You can treat those as upgrades later.
9) Identify where the money will come from to do the project. Consider sources of financing that consider energy-efficiency, such as Renovation 203k loans, low-interest utility loans, and PACE programs that roll the cost of upgrades into your property tax assessment. Calculate payback in several different ways, such as payback period, internal rate of return, utility bills, etc. Use sensible escalators for electricity and fossil fuels in your calculations. Use the useful life of your PV system as a time period.
10) Hold a design meeting with your team before finalizing design. Often called “charrettes”, these meetings bring your team together to understand the goals and expectations, brainstorm design ideas you haven’t thought of, catch mistakes beforehand, and reality-check the design prior to submitting to the City. It might cost you $1,000 to get all this experience in a room, but it can save many times that.
What We Did
Since buying the house, we have completed most of the design steps. Some of our experiences follow below for each step above.
1) Finding a house: we had a scare when we began thinking about what a roof-mounted PV array could generate on our dream house. Using a solar generation simulator, we were alarmed to find our roof classified as “not suitable for solar generation”. The mature magnolia trees along the south lot line cast enough shade on the roof that the Solar Map did not recommend our house for solar generation. An email to our friends at the City found that magnolias, while no longer recommended today for new plantings in our city, cannot be removed for the purpose of access to the sun. The Solar Rights Act is a fascinating example of traditional law running up against unforeseen consequences of rooftop PV generation — the law protects existing solar panels from new objects that might impede solar energy production, but does not provide for removal of pre-existing objects that would reduce solar energy production. This makes sense, as a one-story house next to a residential tower can’t insist the tower be torn down to allow for PV panels to be put on the roof. But there may be opportunities for forward-thinking cities to examine their tree policies and allow for replacement of higher-water-demand, high-growth, shallow-root, evergreen trees with more appropriate trees that preserve neighborhood beauty while allowing for improved PV output, passive solar heating, and lower water use.
Fortunately, our friendly local solar installer, Solar Source, came out that same day and reassured us that our roof was practical for PV installation.
2) Energy audit: We wanted to set a baseline to measure improvement and give people an idea how typical housing stock performs after 50+ years. Our Energy Audit found asbestos in the attic where the heating ducts connect to the “boots” in the walls that transition to the grills in the walls. The auditor said half the time they discover an unsafe condition, such as this, that prevents them from actually performing the duct and blower door testing.
3) Solar Study: Preliminary meetings confirmed roof surfaces facing east and west could be used for PV generation at about 85% of what a south-facing roof might generate. PVWatts and the contractor’s own programs confirmed the 85% figure for east-facing panels, and gave us a site-specific estimate to confirm we could get to net zero with existing roof space and calculate how many panels it would take to get there. It also gave us cost and incentives. The 30% federal tax credit is the main incentive in our area today, and we found it is not a function of income levels, Alt Min taxes, etc.
4) Labels: Build it Green helps ensure sustainability and performance, and serves as advertising for the project’s green attributes. A HERS rating gives a quantitative measure of the home’s performance relative to similar new and existing homes. Energy models will predict energy usage for us to measure actual usage against.
5) Goals: Our goal is mainstream demonstration of readily available technologies to attain near net zero site energy. Local contractors will be used wherever possible. The project will be made public to expose the community to different ways of thinking about remodeling projects. We will carefully manage indoor air quality throughout the course of the project and create an appealing living space that many families would embrace and feel comfortable in.
6) Reconfigure space: In our case, we needed to take a 2 BR, 2 BA house with dated chopped-up interior and turn it into a 3 BR, 3 BA with office and open floor plan. We wanted passive solar orientation to be carefully thought-out, breezes to flow through the living areas, outdoor spaces to flow out of the interior and be practical and inviting, and our children’s need for privacy and hang-out spaces to be successfully met. It needs to fit the neighborhood but not look 50+ years old, giving some clues that all is not typical inside.
7) Model the Energy Usage: I already knew Energy Pro software for California energy code compliance (Title 24). I used two versions of the software to model before and after energy usage, test what-if scenarios, and send the design to other professionals for their own analysis. I used NREL’s software, BeOpt, to give another estimate of energy use and test more what-ifs. I went over past electric and gas bills with a fine tooth comb, and downloaded a full year’s of hourly electric usage from my Smart Meter to determine peak loads, and tease out estimates of cooling, heating, lighting, hot water, and other electric loads. Each family is different, so these served as valuable starting points to the energy use models post-renovation.
8) Incentives: Energy Upgrade California will contribute up to $4,500.
9) Financing: We plan to use a 203k renovation loan to finance much of the renovation over 30 years as part of our home mortgage. We may look to Energy Upgrade California low-interest loans as another source, and the rest will come out of savings.
10) Design Meeting: We held a design charrette to go over the energy efficiency features of the home with our team all in one room. Our architects, builder, and electric utility shared experiences with various materials and systems, with the Net Zero Nest goals in mind. Some of the key items discussed included under-floor air ducts, hydronic heating (using the hot water heater), ductless mini-splits, fiberglass windows, and expected energy usage of the house. After the meeting, we modeled three alternative mechanical systems: ductless mini-split HVAC, hydronic heating, and conventional HVAC.