What is a Passive House?
A passive house, also known as passivhaus or passive solar house, is a highly energy-efficient building design that reduces the need for conventional heating and cooling systems.
It achieves this through a combination of features such as
- Insulation
- Airtight construction,
- High-performance windows,
- And heat-recovery ventilation.
The primary goal of a passive house is to maintain a comfortable indoor temperature year-round while reducing energy consumption.
These houses are designed to capture and retain solar heat during the winter while shading and ventilating to keep cool in the summer, hence the term “passive” solar.
Passive houses adhere to strict energy efficiency standards and often use renewable energy sources to achieve as little energy consumption as possible.
We will look at other aspects of a Passive House further below.
Features of a Passive House.
INSULATION
Passive houses have thick insulation in walls, floors, and roofs to reduce heat transfer between the interior and exterior. This helps maintain a stable indoor temperature and reduces the need for heating and cooling.
AIRTIGHT CONSTRUCTION
Passive houses are built with airtight seals around doors, windows, and other openings to prevent drafts and heat loss. This ensures that the indoor environment remains comfortable and energy-efficient.
PASSIVE HOUSE WINDOWS
Passive houses also have triple-glazed windows with low-emissivity coatings and insulated frames. This helps to reduce the heat transfer while allowing natural light to enter.
These windows also help maintain a consistent indoor temperature and reduce energy consumption.
HEAT-RECOVERY VENTILATION (HRV)
HRV systems in passive houses extract stale air from the interior and replace it with fresh outdoor air while recovering heat from the outgoing air. This ensures good indoor air quality while reducing heat loss, improving energy efficiency.
PASSIVE SOLAR DESIGN
Passive houses are built to maximise solar gain during the winter months, with large south-facing windows and minimal shading. In the summer, overhangs or external shading devices prevent overheating by blocking direct sunlight.
THERMAL BRIDGE-FREE CONSTRUCTION
Passive houses reduce thermal bridging, which happens when materials with high thermal conductivity create pathways for heat to escape.
This is achieved through careful detailing and insulation strategies to maintain uniform temperatures throughout the building envelope.
ENERGY-EFFICIENT APPLIANCES AND LIGHTING
Passive houses use energy-efficient appliances, lighting fixtures, and electronics to further reduce energy consumption. This includes LED lighting, ENERGY STAR-rated appliances, and low-power electronics.
RENEWABLE ENERGY INTEGRATION
While not a strict requirement for passive house certification, many passive houses incorporate renewable energy sources such as solar panels, wind turbines, or geothermal heat pumps to achieve net-zero or near-zero energy consumption.
Passive House Standards in Ireland.
According to Varming.ie, one of Ireland’s premier Passive Housing consulting engineers,
”Passive house buildings must:
- Have an annual heating and cooling demand of no more than 15kWh/㎡ or it must be designed with a peak heat load of 10 W/㎡.
- Have a total primary energy (the energy used for heating, hot water, and electricity) of not more than 120 kWh/㎡ per year.
- Not leak more than 6 times the house volume per hour as tested by a blower door, or less than 5 cubic feet per minute taking into account the surface area of the enclosure.”
5 Numeric Principles for the Construction of a Passive Houses.
According to the Passive House Institute, you should consider the following:
THERMAL INSULATION
All opaque components on the outside of the house must be very well-insulated. For cool-termperate climates, this means a heat transfer coefficient (U-value) of 0.15 W/(m²K) at the most.
WINDOWS
Window frames must be fitted with low-e glazings filled with argon or krypton to prevent heat transfer. For most cool-termperate climates, this means a U-value of 0.80 W/(m²K) or less.
VENTILATION HEAT RECOVERY
In a Passive House, at least 75% of the heat from the exhaust air is transferred to the fresh air again by means of a heat exchanger.
AIRTIGHTNESS
Uncontrolled leakage through gaps must be smaller than 0.6 of the total house volume per hour.
ABSENCE OF THERMAL BRIDGES
All edges, corners, connections and penetrations must be planned and executed with great care, so that thermal bridges can be avoided.
What are the downsides of a Passive House?
While Passive Houses offer numerous benefits, they also have some potential downsides.
COST
Due to the advanced building techniques and materials required to build a passive house, the initial cost of construction can be higher than building a traditional house.
A passive house may cost 16-25% more than a traditional house on average.
DESIGN INFLEXIBILITY
Achieving Passive House certification may involve strict standards that could limit design flexibility. You would often hear people say that passive houses look plain and boring.
The main reason for this is that at this time, those designs are the perfect designs for energy-efficiency. However, with time, we believe that passive housing technology would improve such that passive houses can be built with a lot more personality and character.
MONITORING
Furthermore, maintaining airtightness over time requires careful attention to detail during construction and regular monitoring, which could pose challenges for some homeowners.
Can you turn a normal house into a passive house?
Yes, it is possible to retrofit an existing house to meet Passive House standards, although it may require significant renovations and investment.
Retrofitting typically involves improving insulation, upgrading windows and doors, enhancing airtightness, and installing a mechanical ventilation system with heat recovery.
While transforming a conventional house into a Passive House can be challenging and costly, it offers long-term benefits such as reduced energy bills, improved comfort, and lower environmental impact.
Standards Passive Houses in Ireland Must Meet.
According to Selectra, Ireland’s premier energy and broadband comparison site, you need to consider the following:
CONSUMPTION
Total energy consumption (including electricity) must not be over 60kWh/m2 per year.
HEATING & COOLING LIMITS
The heating and cooling demand of the building must not exceed 15 kWh/m2. So a small semi-detached house exceed 3000 kWh per year.
AIRTIGHTNESS
Air must not exit the building at a rate of more than 0.6 times the house volume per hour. A blower door can and should be used to evaluate whether the house complies with this standard.
Performance targets for a European climate
| Passivhaus | EnerPHit | ||
| Airtightness n50 | ≤ 0.6 ACH @ 50 Pa | ≤ 1 ACH @ 50 Pa | |
| Space Heating Demand (SHD) | ≤ 15 kWh/m².a | – | ≤ 25 kWh/m².a (variable)* |
| Peak heating load (alternative criterion) | – | ≤ 10 W/m² | – |
| Primary Energy Renewable (PER) | ≤ 60 kWh/m².a | ≤ 60 kWh/m².a (variable)* | |
| Space cooling demand | ≤ 15 kWh/m².a | ≤ 25 kWh/m2. yr | |
| Surface temperature | ≥ 17 °C | ≥ 17 °C | |
| Overheating | Max 10% > 25°C | Max 10% > 25°C | |
*Copied from PassivHaus Trust
Conclusion
To conclude, passive Houses offer a promising solution for sustainable living, with an emphasis on energy efficiency and comfort. While they can be costly and also have strict standards, the long-term benefits justify the investment.
So whether you want to build a new Passive House or retrofit an existing one, the principles and insights shared in this blog post can guide you towards a greener home.
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