To get to “net zero”, they are building a tight building envelope with energy-efficient windows, blown-in cellulose insulation, an efficient heat pump water heater, and plenty of PV cells on the roof. This would be enough to make the project remarkable in this region. But these homeowners have taken the project much farther, to the point of making it an intellectual and philosophical challenge.
The Fortunatos, owners of the home, are blogging about the experience of building their home this way. Perhaps because of the full disclosure of every decision they make, they are taking the time to dig deeply into the pros and cons of each design decision and material choice. They would like to help others think about how decisions they make for their home should be dictated by their specific lifestyle. And there are some eye-opening conclusions on their website for you to consider in building your own home.
For instance, installing tankless water heaters and solar thermal panels has become a common practice in green home building. Instead, the family chose a multi-tank solution that first pre-conditions the city water to ambient temperature, which at the beach is quite often 75 degrees, a savings of 20 degrees worth of energy use. Then they utilize a new technology heat pump that has efficiencies far in excess of traditional gas burners used in tank and tankless heaters. While tankless water heaters have widespread advantages in certain situations, there are no one-size-fits-all solutions in green building. The owners thought about water heating in terms of how best to support their lifestyle and generate return on investment; in their case – 3 people who are often out of town travelling – a solar thermal system and tankless water heater were not the answer.
The building design also takes into account orientation to the sun to keep sun out in cooling periods and welcome it in during heating periods. The southern exposure is the culmination of this philosophical debate. Using quantitative models, they arrived at a 5-foot overhang over the windows on the front of the house, carefully calculated to shade the building from the sun in summer (high up in the sky) and to allow the sun to heat a thermal mass wall in the master bedroom during winter (when the sun is low in the sky). Decisions like this can save significant amounts of energy, and are modeled by Energy Soft when an energy consultant evaluates a project. Every window is entered into the model with a specific compass orientation and overhang dimensions, so that passive energy use can be considered.
The homeowners are also looking deeply into the insulation design on their project. Once the solar arrays had been specified and they knew the energy their home would produce, they could design the building envelope to release only a known amount of energy. They settled on blown-in cellulose insulation between the framing members (many of which are reused 2x4s), for an R-value of about 13. Rather than install foam on the exterior of the framing, commonly known as Continuous Insulation or CI, they determined that vapor permeability of wall systems is a desirable feature for air quality and mold resistance. Their search for an energy efficient alternative to foam insulation led them to fiber board, a natural vapor-permeable material that adds an R-value of 2.6 for every inch of thickness. Together with the blown-in insulation, their wall systems achieve an insulation value sufficient to realize their goal of “net zero”, together with all the other good decisions they have made throughout the house.
Next they had to choose an exterior cladding system that is attractive and protects the building from the elements. They determined early on that they wanted to incorporate recycled content into their project, while minimizing embodied energy (the energy used to produce the materials in their home) and minimizing energy loss through the walls. They are using metal panels on parts of the building, and plaster elsewhere. The plaster will incorporate recycled content from locally-sourced recycled concrete aggregate and flyash. The flyash question is a debate in and of itself, with questions of heavy metals, coal-fired power plants, and long-term maintenance to consider. As with every other decision on the house, the Fortunatos considered all the angles in deciding whether to use materials that incorporate flyash and divert it from landfills.
Build Smart Group advised the owners on plaster material decisions, including fiber-reinforced base coats with recycled content, color coat stucco finishes based on recycled aggregates, and lime plasters with lower embodied energy than cement-based alternatives (and stunning good looks). Merlex Stucco’s website is a good source of inspiration in this area http://www.merlex.com/sustainable_stucco_how_to.htm.
This project should serve as an inspiration to all green-minded homeowners to carefully consider how their new home fits their lifestyle. Rather than leaving the key decisions up to design professionals working in a vacuum, owners should fully inform their design teams of their values and lifestyle and what green means to them. After all, for those blessed with the resources to create the home of their dreams, a home should say “This is our home. This is who we are.”
