If you’re looking for a more energy-efficient way to live, you might be considering building a passive house. Following a set of basic principles to make the most of passive energy sources in the home, rather than active heating and cooling systems, passive houses can reduce energy bills by as much as 90%.
But how do they work, and how feasible are they really? Below, we take a more in-depth look at how a passive house is built, and how much you can expect to pay for one.
The 5 principles of passive house
In Europe, homes built to the passive house standard must meet a specific set of criteria regarding space heating, primary energy consumption, thermal comfort, and airtightness. The same is true in the US, however, due to the size of the country, and the wide variety of climates, setting a specific set of criteria for the entire continent is unfeasible. Different areas have different standards, which you can check out here.
To meet these strict criteria, passive houses follow 5 principles:
- Solar orientation; the building must be built in such a way that it maximizes the natural sunlight in colder times, without overheating during warmer months.
- Insulation and zero thermal bridging; high-quality insulation is used to ensure minimal heat loss. An insulating envelope wraps the entire home and removes any thermal bridging, i.e. gaps in insulation.
- Airtight; the insulation envelope also ensures that the building is airtight, preventing the uncontrolled flow of air.
- High-performance windows; top quality, certified double or triple pane windows add extra insulation while optimizing the sun’s energy.
- High-performing ventilation; airflow is controlled throughout the building by a sophisticated ventilation system, which transfers heat energy from outgoing air, into the incoming air. In this way, a constant supply of fresh air at the correct temperature is provided.
Building a passive house
Houses built in accordance with the passive house standard typically utilize the following technologies and techniques.
Making the most of the sunshine
Meeting the strict criteria set out by the Passive House Institute requires careful planning and meticulous design that makes the most of passive energy sources, namely, sunlight and shade. Everything from the placement of the building to the window size is in accordance to the position of the sun, both in summer and winter, to exploit sunlight when it’s needed most, and to prevent overheating in warmer months. Anything from the pitch of the roof to the type of glass used in the windows can also be used to optimize the sun’s energy.
Keeping the heat in
Passive homes are typically ‘wrapped’ from top to bottom in a continuous envelope of insulation, creating an almost airtight layer. Double walls prevent colder, exterior walls from cooling the building down too quickly, and enable the house to stay warmer, longer. The downside is that you may lose some internal floor space, but this can be planned for.
Ensuring fresh air at a constant temperature
A sophisticated mechanical ventilation system draws in fresh air from outside, which is then filtered, before passing through a subsoil heat exchanger, and then an air/air heat exchanger. The fresh air is then dispersed throughout the building, having been warmed or cooled to the ambient temperature of the building.
A series of vents, mostly located in warmer, damper areas of the home, such as the kitchen and bathroom, draw in the stale air, sucking it through the heat exchanger to recover the heat and pass it onto the fresh air, before being expelled outside.
Further reduction of energy consumption
Low energy appliances and fixtures are normally fitted, such as low voltage, smart lighting designs. Renewable energy sources can also be employed, such as solar-powered outdoor lighting and solar panels.
The cost of a passive house
If you’re planning to build a passive house from scratch, you can expect to pay around 5-10% more for a typical family home. However, the energy savings can recoup the initial loss over a few years. Larger, multifamily buildings will typically only cost 0-3% more than a traditional building, due to economies of scale.
With more and more window and door manufacturers focusing on more energy-efficient products, however, it’s possible that prices will drop, and the gap will close. Other sources claim to have built a home to passive house standards for just $165 per square foot. While this may not yet be the norm, there is a chance that such pricing will become more common.
Despite the strict nature of the construction, you don’t need to build a new house from scratch to create a passive house. Many older homes can be retrofitted to meet the passive house standard by improving the ventilation, windows, and insulation. This option may not always be viable, however, and it’s worth doing your research before buying that fixer-upper in the hopes of transforming it into a passive house.