Using Passive-House Design to Achieve Net-Zero Buildings
by Natalie Leonard, founder & president, Passive Design Solutions
(Editor’s Note: Natalie Leonard is the first Certified Passive House Consultant® licensed to deliver the Certified Passive House Builder training in Canada. As an engineer and the president of Passive Design Solutions, she has worked on over 100 Passive House projects that are net-zero ready and provided support to over 30 builders on their first Passive House projects. Committed to reducing the housing industry’s notable carbon footprint, the team has recently launched a line of ready-to-build Passive House design plans, available online to the general population.)
It is not by accident that residential project renderings are most often set in natural surroundings. From the bucolic to the breathtaking, a natural context gives buildings their brilliance with each rendering striving to strike the perfect balance between built and natural elements to make an irresistible scene.
Perfect, right? Not entirely, as these renderings present a paradox. If we agree that human activity contributes to climate change and that too often that change is destructive, then we must also agree that the houses we design contribute to the destruction of the very environment in which we imagine them situated. Knowing this, what can be done to resolve the paradox?
In the residential sector, net-zero construction using passive house design is one solution. A zero-energy building produces at least as much renewable energy as it uses in a year, when accounted for at the site. Passive house describes a set of design principles and defined boundary conditions that, if applied holistically, lead to a building that remains comfortable with only minimal active heating or cooling during extreme climate conditions.
A net-zero house is not necessarily built using passive-house design, and a passive house is not necessarily net zero. Net zero is a calculation, one that ensures site energy supply and demand are in balance. Passive-house design results in ultra-low heating-energy demand and with its minimal heating energy requirements, provides an excellent foundation for any net-zero project.
Given its much lower energy demand, a passive house provides a practical way to balance the net-zero equation at modest cost. Construction costs may increase 5% to 15% over code-built alternatives, but passive houses achieve a 75-90% reduction in heating costs, with annual heating bills as low as $150. The reduced demand for on-site energy production means fewer solar-voltaic panels are needed to reach net zero. Net-metering grid tie-in eliminates the need for batteries and greatly simplifies power management. The result is a much less expensive power generation system that can be amortized in 5-12 years, depending on local costs and availability of efficiency incentives.
The Passive house achieves these savings by following simple design and build rules: site the structure to take advantage of solar energy and prevailing winds for heating and natural ventilation for cooling; design the envelope to be air-tight, super-insulated, with upgraded windows and doors, all to minimize heat loss/gain in all seasons; use compact building shapes that reduce exterior surface area and opportunities for air infiltration and thermal bridging; design and orient the roof to anticipate installation of solar photovoltaic panels; specify that mechanical systems have ultra-efficient ventilation to ensure consistent indoor air quality without unnecessary energy loss; and avoiding fossil fuels and specifying electrical systems that have only high-efficiency components.
What does the marketplace say? Many homebuyers today want the quality, comfort, and energy savings that come with passive houses, and they want the carbon emissions reductions that come with net-zero houses. They also want lower energy costs and increased energy security, two goals that are especially important to young cost-conscious families and seniors needing to manage fixed assets. Net-zero passive house design that uses modest on-site, grid-tied, electrical power generation, is a simple and practical path to reach these objectives in most locations and for most climates. For a small increase in construction costs buyers will receive significant continuing benefits, including: up to 90% reduction in heating energy over a conventional new home; total energy costs cut by 65%-100% and a reduced carbon footprint; superior indoor comfort, including the bright, draft-free, and consistently warm spaces are what owners love most about living in their passive house; exceptionally quiet spaces that are isolated from outside sounds even during storms; operational and maintenance tasks are much easier due to simpler mechanical systems; high-quality ventilation equipment provides conditioned fresh air in the living spaces; and increased safety and security during storms.
If a rendering represents the idealized expression of a design, then perfecting the rendering requires that the built and natural elements be in harmony, the harmony that can come from passive-house designs that achieve a net-zero effect on our environment.