Passive houses use high standards of insulation that reduce heat loss to very low levels. Combined with high performance windows and carefully designed shading, these homes require very little supplementary heating.
To maximize its insulating effectiveness, insulation must wrap the building uninterruptedly. Any interface details that bypass it create thermal bridges and can significantly reduce a building’s energy efficiency.
Energy Efficiency
Unlike traditional buildings, which consume large amounts of energy for heating and cooling, passive houses rely on the sun, internal heat gains from people, cooking and plug loads, and an incredibly airtight envelope with continuous insulation. The result is near-zero energy consumption, and a building that maintains comfortable temperatures year round without the use of an HVAC system.
Insulation is measured by its thermal resistance or R value in both metric and US customary units. The higher the R value, the greater the insulating effectiveness. The R value is determined by dividing the thermal conductivity of the material by its density.
Passive houses achieve a high R value by using continuous insulation around the entire structure. In addition, they install high performance windows and doors that reduce solar heat gain and maximize natural breezes to cool the interior in summer.
While high R values are important, it’s also crucial to focus on installation details. Poor installation can decrease the efficiency of the insulation and increase drafts, moisture, and mold.
A well-designed building meets the passive house standard when it has an airtight, super-insulated enclosure and balanced ventilation that uses a heat recovery ventilator (HRV) or energy recovery ventilator (ERV). The HRV or ERV helps to maintain the interior humidity level while removing stale indoor air, and transferring the heat from stale indoor air into fresh incoming outdoor air. This process is known as “supply air heating” and is only possible in appropriately insulated buildings.
Thermal Comfort
Thermal comfort is the ability to stay comfortable in your home no matter the season. The heat loss of your building envelope during winter and the solar gain of your home in summer are controlled by insulation and passive design techniques to make sure you can enjoy your home all year round without consuming much energy.
The quality of the insulation and its installation plays a crucial role in passive house performance. The insulation should be continuous around the building and free of interface details such as structural elements or windows. These gaps can reduce the efficiency of super-insulated buildings because they allow hot and cold air to flow freely. They can also create cold spots inside the building and cause condensation, which leads to mould growth. This is why it is important to minimise thermal bridges and to aim for continuous insulation, such as the use of aluminium cladding in Passive House projects.
The thermal performance of your insulation is measured by its R value (in metric and US customary units) or U value W/K-1m-2. The higher the R value, the better the insulation performs. Suitable bulk insulation for tropical climates includes foil-faced polystyrene boards fixed between battens, or plasterboard bonded to rigid foam board with either a vapour control or water-resistant membrane. The required R value will vary according to the climate zone in which your home is designed.
Indoor Air Quality
The quality of indoor air is another key component to a healthy home. Many pollutants can accumulate in insulated buildings, and while some, such as radon, are easily monitored, others are less obvious and may take years to show symptoms.
Poor ventilation can lead to condensation and rotting construction materials. It can also promote microbial growth that can cause respiratory problems. Airflow is essential to a healthy indoor environment, and passive house designs can ensure good ventilation with mechanical or natural means.
Insulation can be used to reduce the amount of mechanical ventilation needed to support comfort and good indoor air quality. It can also help protect a building against the accumulation of moisture and other contaminants in cavities.
Different insulation materials have differing abilities to resist conductive heat flow. This is referred to as their R value, and it is important to have an appropriate R-value for the climate zone of your home.
Passive House standards require a high level of energy efficiency and an airtight envelope with continuous mechanical ventilation with heat recovery (MVHR). The MVHR system filters incoming air to remove most airborne particles, including pollen, dust, cigarette smoke, and even COVID-19. This can significantly improve indoor air quality. However, the filtration system does not remove all pollutants, and some can be released by heating systems.
Durability
A well-insulated building envelope largely eliminates the need for mechanical heating and air conditioning, significantly cutting cooling and heating costs. This results in lower emissions and energy consumption while providing superior comfort. The bulk insulation in passive houses is made from low-conductivity materials, resulting in a high R-value (in SI units it is called U-value).
For the insulation to be effective it needs to completely encase the whole building. Any material that bypasses the insulation, such as studs or steel beams, reduces its effectiveness. This is called a thermal bridge and must be minimized. The ideal is to have a continuous layer of insulation encasing the structure, but this is not always possible due to structural elements. Therefore, any gaps between insulation must be carefully minimized and filled with a suitable material.
In addition to the energy performance of insulation, a passive house also features high-performance windows that maximize solar heat gain in winter and limit unwanted heat loss in summer. In conjunction with passive solar design and airtightness, this results in a building that requires only very little heating and can even be heated entirely by fresh, outdoor air. This is also known as supply air heating. The high-performance windows are also designed to minimise condensation and thereby protect the wood frames from moisture damage. These factors combined with a highly efficient ventilation system based on heat recovery from the air supply help to achieve an energy demand that is less than one-tenth of the typical heating demand in conventional buildings.