Environmentally conscious families, planning to build a custom home today, are concerned about their carbon footprint and sustainability. As they plan their new home, British Columbia residents soon come across the BC Energy Step Code website and the high-performance staircase.
The Province of British Columbia introduced ‘energy’ as an objective for the BC Building Code back in 2008, giving both builders and designers the option of using the measures either as a prescriptive or performance approach to meeting the building code’s efficiency requirements.
Most of the builders to date have chosen the prescriptive approach. In other words, if the municipality requires them to meet or exceed the Step 4 efficiency requirement, that’s their target. A performance-based approach focuses instead on the target outcome – i.e.: net zero ready or net zero – and the Step Code leaves it to the design and building team to then determine how they’re going to meet the Step 5 target.
Net Zero and Passive House are two concepts that have gained significant traction over the past few years. Both share a common goal – minimizing energy consumption and greenhouse gas emissions – but there are variations in the way they achieve this goal. In this article, we will explore the synergy between the two principles and how building a passive house can serve as your path to achieving net zero status.
What is net zero, or net zero ready?
When designing a net zero or ‘net zero ready’ home, the focus is on achieving a balance between the energy your home will consume and the renewable energy it produces. Over a year, your total energy consumption must be equal to or less than the energy generated by renewable sources. Striking that balance effectively results in “zero” energy consumption.
A net zero home and a ‘net zero ready’ home are both built to the same standards of energy efficiency. The net zero home has a renewable energy system such as solar panels and/or wind turbines installed, whereas the net zero ready home is designed and built to have the system installed at a later date.
To achieve net zero, your home will employ various energy-saving strategies and systems. Energy-saving techniques include high-efficiency HVAC (heating, ventilation and air conditioning) systems, a sealed building envelope, elimination of thermal bridging and advanced insulation to reduce energy loss. Renewable energy sources such as solar panels or wind turbines are integrated into the home’s design to generate clean on-site energy.
For net zero ready homes, the renewable energy source minimum requirement will be specified by the energy modelling software, and the system can be installed at a later date. The home will often already be wired for the renewable energy system.
And what is Passive House?
In contrast, passive house is an architectural and building standard. Passive house focuses on achieving maximum energy efficiency through a holistic approach to design, construction, and ongoing operation. The core principles of passive house design are:
- Superior insulation is specified for building your passive house, as compared with a conventional home. The home’s super-insulation provides a measurable continuous thermal barrier between the heated or cooled air inside and its outside environment. In addition to retaining heat during the winter, and keeping it out in the summer, continuous insulation will significantly improve the comfort of your home, preventing the development of condensation and uncomfortable cold spots. A passive house is designed not to exceed 25°C for more than 10% of the time, to support comfortable temperatures during the summer. In the winter, it is designed to always be at least 20ºC.
- Airtight construction helps maintain your home’s internal temperature, eliminating any draughts or leaks, while controlling moisture. Homes must meet the Passive House Institute standard, with a maximum of 0.6 air changes per hour at 50 Pascals pressure (ACH50), as verified with an onsite pressure test (in both pressurized and depressurized states). To verify that your home meets the passive house standards, a blower door test is completed to determine how much air leaks out of the house. Your passive house must score below a 0.6ACH50 to pass certification.
- High-performance windows and doors require double or preferably triple glazing, and the frames will need to be non-thermal conductors. The windows must be perfectly sealed to contribute to the building’s airtightness. The sizes of your windows is also a very important consideration, and these will vary depending on the orientation. Your windows will allow more sun to penetrate during the winter months, to provide needed warmth, while minimizing the heat from the sun during summer months. Your windows can help reduce energy costs by flooding your rooms with natural light. Or, windows with one or two low-e glass panes can decrease the amount of light that enters your living space. Double or triple-pane windows are also effective at reducing the level of noise that enters your home from the outside while providing you with additional privacy.
- Mechanical ventilation with heat recovery (MVHR)
Your certified passive house ventilation system filters fresh air into your home, completely replacing the stale air with fresh, filtered air every three hours. You are still able to open windows, but the outdoor air will not have the dust, pollen and smoke filtered from it. Because you’re not recirculating the same air throughout your home there should be a reduction in shared illnesses.
Your MVHR system is designed to recover warm and cool air, returning it to the incoming stream. This saves you heating and air conditioning costs while maintaining consistent internal temperature and humidity levels.
High-quality ventilation also removes much of the humidity, reducing the risk of condensation. Humidity levels of passive houses must not exceed 12g/kg for more than 20% of the occupied time (60% relative humidity at 25ºC).
- Minimizing thermal bridging prevents heat from travelling in or out of your home through the framework, studs and window and door casings. Installing rigid insulation panels over the exterior, beneath the exterior cladding, prevents the most common sources of thermal bridging. Most PVC and fibreglass window manufacturers today utilize bulky hollow extrusions injected with polyurethane insulation, eliminating the frames as a source of thermal bridging.
- Optimal solar orientation and shade
While not one of the 5 essential principles, solar orientation and tree shade are important factors in passive solar design. When building a passive house or net zero home it’s of considerable value to orient your home so that it capitalizes on the sun’s free energy. Building orientation, daylighting and thermal mass are all important considerations of passive solar construction.
If the structure is not on reasonably flat land, a passive solar house should be built on the south-facing slope of a mountain to avoid the extreme shading created by the low-angled sun blocked by the mountain.
The synergy between net zero and Passive House
While two distinct concepts, net zero and passive house share fundamental principles that make them highly compatible. When the passive house standard becomes the path to achieving net zero, a powerful synergy is created that can significantly reduce your home’s energy consumption and carbon footprint.
Energy efficiency is the core principle and it’s the emphasis in both concepts. Passive house focuses on superior insulation, airtight construction, eliminating thermal bridging, and high-performance windows and doors, setting a solid foundation for minimizing energy consumption and your home’s carbon footprint.
By building to the passive house standard, your home can significantly reduce its heating and cooling loads, which will lead to lower energy bills and a reliance on fossil fuels. The Passive House Institute (PHI) standard presents clear, easily achievable pathways to achieving net zero or nearly net zero in both new home builds and retrofits.
Comfort and indoor air quality are two Passive House priorities. The mechanical ventilation with heat recovery (MVHR) system delivers a constant supply of fresh, filtered air while maintaining a comfortable indoor temperature.
The net zero goal is to create a sustainable building that generates as much energy as it consumes, a home that is up to 80% more energy efficient than a home built to conventional standards. By creating a comfortable, healthy living space your family can enjoy those long-term energy savings.
Long-term sustainability is inherent to both the net zero and passive house approaches. By reducing your energy consumption and greenhouse gas emissions, you are contributing to a healthier planet. The long-term sustainability of passive house/net zero buildings extends well beyond their initial construction. They are built better and will remain efficient and effective throughout their lifetime. This will save money and resources by reducing the need for energy-intensive maintenance, renovations and retrofits.
Reduced environmental impact is the result of combining net zero and passive house principles. Passive house lowers energy consumption, while net zero offsets those reduced energy needs with renewable energy. This reduction in emissions reduces your family’s environmental impact and helps promote a more sustainable future.
Financial benefits from net zero homes can be substantial. The initial investment for a net zero ready passive house will typically be 5% higher, and the long-term energy savings typically lead to a return on investment within a few years.
Government incentives, rebates and tax credits are often available to encourage the construction of energy efficient buildings, further reducing the initial investment.
Renewable energy integration
Solar panels, wind turbines, and geothermal systems are common choices for incorporating a renewable energy source to offset your energy consumption. The synergy arises when your passive house’s energy efficiency measures have reduced your home’s energy demands to a level where a small renewable energy source can cover its needs entirely. This will not only reduce your upfront costs for renewable energy installation but also make your home more resilient to any fluctuations in the energy supply.