The Bellingham Affordable Net-Positive Home is a new 2 bedroom home with a Built Green certification rating of 5 stars. The building is currently housing its original residents and has reliably provided enough power to allow them to live independent of the public power grid. Energy efficient Structural Insulated Panels (SIPs) construction required a special inspection process to meet code.
Normally during building construction, the framing is put up and then inspected. However, the use of SIPs panels cover the framing before it can be inspected. To comply with the code, the inspector was required to visually inspect the base plate connections before the SIPS could be installed. An engineer was also required to inspect them and sign off that they were installed correctly. Though these problems increased the challenge in building this home, the technologies they allowed the use of were vital to achieving the goal of the home.
Exterior walls of structural insulated panel construction shall be designed and constructed in accordance with the provisions of Section R614. SIPs shall be fastened through both facing surfaces to other wood building components. Use of SIPs in residential homes beyond the scope of Section R614 will require a licensed engineer to approve the build plans before construction begins.
Inspectors are generally unfamiliar with Structural Insulated Panels (SIPS).
Part of the framing that is typically inspected after installing the mechanicals but before covering the insulation is covered up, leaving it inaccessible to the inspector.
The building inspector was required to make additional site visits to inspect base plate connections before installing each level of walls.
An engineering firm was hired to approve the building plans before construction began.
The current residents were in search of a new home, and decided to build their own instead of purchasing an existing one. One of the incentives to building their own home was that it could be custom designed. After touring the home of Ted Clifton of TC Legend Homes, they chose his company to handle the construction of their new abode. A primary goal of the custom design and build of their new house was to be a net-positive living space with the most efficient and cost effective options available.
Because energy efficiency was so important in the design of this home, many unusual technologies were implemented. Insulation was optimized to reduce heat loss through the air. SIPs panels were implemented, which reduced air loss by 50% while also reducing the amount of waste material included in the building. A concrete floor was chosen because it is essentially a free finished-floor, is cost effective and can be used as a thermal mass. To further reclaim heat that would be lost in a conventionally built home, a Heat Recovery Ventilator (HRV) with 90% efficiency was used. Thicker windows were also utilized to decrease the amount of heat energy that would be lost. To reduce water usage, low flow toilets and faucets were used, with future plans to add a water catchment system. Energy Star rated appliances were used wherever possible to reduce electrical energy usage.
The project was custom designed by the owners, and the result was a net positive house with a HERs rating of -25, and a Built Green rating of 5 stars was built in 7 months. As the goal of this project was to be net positive, all parts of the house needed to be optimized, and the HVAC system was an important consideration in this. To improve performance, a Mini Split heat pump was installed. Where normal HVAC systems have a performance ratio of approximately 1:1, the Mini Split can achieve ratios as high as 4:1. While this element is one of the largest contributors to efficiency of the building, it was also one of the largest hurdles of the build process. Heat pump HVAC systems such as the Mini Split are relatively new, and it is difficult to find contractors who have the knowledge to install them properly.
Another design aspect that contributed to the net-positive goal was the Heat Recovery Ventilation (HRV) system. This system uses an air flow heat exchanger to recover heat that would normally be exhausted to the outside. The HRV and Mini-Split Heat Pump are tailored to the rest of the house to work together t optimize heating and cooling loads, balance air pressure and maintain indoor air quality within the airtight building envelope.
Another important design aspect was the Structural Insulated Panels (SIPS). SIPs are foam insulation boards that have a high structural integrity and increased the building’s insulation. Wall panels are manufactured in a factory, shipped and installed by crane in a fraction of the time a framed house can be built. The monolithic panels have very few seams which are sealed with tape to create an extremely airtight building envelope. Another design aspect is the solar panel array. The amount of solar panels used are capable of outputting enough energy to charge an electric car in addition to powering the house. The solar array presented a financial challenge because startup prices were high at the time of the building’s conception. The solution was to wait two years to install the solar array, a decision that saved an estimated $50,000. Finally, all appliances are energy star rated.
The cost to benefit ratio of this project is extremely good. Cost of living expenses are significantly decreased for multiple reasons. The solar array on the roof of the home has the capacity not only to power the home but also charge their electric car, dropping both their electrical and gasoline expenses to zero. This comes to roughly three thousand dollars in savings each year. In addition to this, during periods when the solar panels produce more power than the home consumes, this excess power can be sold back to the power company. The owners have not yet lived a year in their new home, but over the summer months they sold this excess electrical power for five hundred dollars, showing a potential for a yearly payment from the electric company of two thousand dollars. At this rate they will be able to pay off their 20 year mortgage in only 16 years.
While SIPs panels cost more than wall framing materials in a traditional home, they are installed by crane over just a few days, saving a large amount of labor which results in simpler, faster assembly and short project schedule – all significant financial benefits to the owner and/or skilled, qualified builder.
Outside of these monetary benefits there are also other benefits as well. Because the home is net positive, it is helping to reduce human impact on the environment. It is also a very good proof of concept for net positive homes and will lead to an increasing number of homes being built in this way.
The builder has been in the business for nearly 10 years, and has his building process down to a science. However, the owners have identified one area of the home they would like to improve, this being the future addition of a rain catchment system. In order to reduce construction costs, the home currently has no rain catchment system, leaving the home entirely on-grid in terms of water supply. Changing this would further increase the net positivity of the home.