Sustainability consultant Kelly Gillespie of Kelly Green Raters has completed an energy model for the fully contained in-law suite addition at the Model ReModel 2022 project, and the results show an impressive performance.
Based on a projected RESNET Home Energy Rating Score (HERS) of -12, builder Symbi Homes predicts that the 850-square-foot one bedroom, one bath accessory dwelling unit (ADU) will exceed its Net Zero Energy goal by producing more renewable energy than it consumes over the course of a year.
"We are very pleased that the model is showing net positive performance on this brand new accessory dwelling unit, " says Nicole Tysvaer, CEO of Symbi Homes. "This negative HERS score demonstrates that we can build to a very high efficiency standard without significant cost increases, and our homeowners will pay next to nothing on their electricity bill as well."
Homeowners will benefit from an annual savings of $1,726 compared to an average US home, according to the rating.
A HERS of 100 is standard for a newly constructed home today. Anything less than 100 means the home is more efficient than a standard build, and a HERS of 0 means the home is net zero, using as much energy as it produces.
To achieve truly net zero performance, it’s advised that a home hits a HERS -10 due to different variables such as homeowner behavior, which affects energy usage. Model ReModel 2022 achieves that and more with its HERS -12.
The baseline HERS score for Model ReModel's original Victorian home was 188, which means the house was extremely inefficient with a lack of insulation, leaky windows, underperforming mechanicals, and outdated appliances.
Gillespie generated the HERS score by modeling several aspects of the building's design and specifications including insulation R-values, size and type of windows, appliances, solar array, and mechanical systems. The 6.8 kW solar array will produce 7,381 kWh and offset its cost in five years.
Model ReModel will use efficient products such as induction cooktops, ProVia windows and doors, GreenFiber insulation, Titebond sealant and caulks, and mechanicals from Mitsubishi.
The rear ADU is attached, but will have a dividing wall with separate entrance and therefore operates independently from the main house.
"Comparing our HERS scores side by side is quite shocking," explains Tysvaer. "Both units are off the charts, but in opposite directions. With additional upgrades, we hope to improve the Victorian's score quite a bit."