A near net zero building is one whose annual energy requirements are minimized and could be partially or completely offset by renewable energy. Its energy use is reduced to very low levels compared to traditional construction by using energy-efficient design solutions for all aspects of the building. New performance-based codes and targets for building energy efficiency, such as the BC Energy Step Code, allow for many potential solutions to reaching near net zero.
While the necessary thermal performance of the building enclosure depends on factors like climate zone, airtightness, window-to-wall ratio, building shape, size and orientation, and mechanical systems used, a well-insulated building enclosure as part of the enclosure-first approach enables both high performance and design flexibility. Increased airtightness, high effective R-values, and minimized thermal bridging are reliable design solutions for meeting near net zero targets.
A home built to near net zero targets, with a high-performance, thermally efficient enclosure, provides the end user with a noticeable increase in comfort and a durable building. It will also be more resilient to potential climate changes and more likely to align with future code updates.
This guide will instruct the user on how to design and build a future-proof near net zero building using existing, low cost, proven building materials and methods. This guide provides an outline of the principles of designing and constructing a near net zero energy efficient home, including,
Remi Charron (Remi Charron Consulting Services) evaluated close to 2 million HOT2000 models using NRCan's Housing Technology Assessment Platform (HTAP) to support the development of the BC Energy Step Code. He leveraged this experience and conducted additional modelling to establish potential design strategies that can achieve the upper steps of the BC Energy Step Code (Steps 4 & 5) as well as net zero performance per the Canadian Home Builders' Association's net zero home guidelines. The successful design strategies modelled by Remi Charron were combined with industry experience by RDH Building Science to determine value-optimized enclosure performance. Beyond strictly construction cost, optimization for value was determined by also considering each enclosure assembly's effect on occupant comfort, overall constructibility, and end-user operation cost.
Ranges of effective insulation levels needed to meet near net zero targets are given for above-grade walls, below-grade assemblies, and roofs in all climate zones of British Columbia, with the upper steps of the BC Energy Step Code used as example targets. Considerations for
other regions of Canada are also included. This guide will help the reader understand how the building enclosure plays an important role in overall building energy performance optimization for reaching near net zero energy efficiency performance targets.
Eight examples of near net zero assemblies, for above-grade walls, below-grade walls and roofs, are outlined in this guide, including key performance items and construction considerations. The corresponding effective R-values are given for each, showing the range in insulation performance that can be achieved with different insulation types and thicknesses. Five example details are shown to highlight the important aspects of transitions between assemblies that maintain airtightness and insulation continuity.