What is a Passive House?

The Passive House (or Passivhaus, in Europe) standard is a building standard and construction concept designed to drastically increase the energy efficiency, comfort and longevity of a newly built property, or retrofit an existing one.  Developed in Germany by Dr Wolfgang Feist it is becoming increasingly more common as a practical building standard across the UK and Ireland.

The Passivhaus Institute lays down the standard for Passivhaus construction and on completion provides a building certification.

The central concept behind a Passive House is that it can maintain a comfortable indoor temperature and air quality by using very small amounts of heating or cooling to the air.  These buildings largely heat and cool themselves and are therefore considered ‘passive’. Key features of a Passivhaus Standard Building include:

  • Very High levels of insulation
  • Excellent Airtightness
  • Eliminate thermal bridging and cool spots
  • High quality triple glazed windows and doors
  • Mechanical Ventilation with Heat Recover using air-to-air heat exchanger
  • Optimisation of passive solar gain
  • Low heating demand

EnerPHit is a slightly relaxed standard for retrofit projects, where the existing architecture and conservation issues mean that meeting the Passivhaus standard is not feasible.

The first houses built to Passivhaus standard were completed in 1991, and since then there has been extensive monitoring of Passivhaus buildings which has demonstrated conclusively that they deliver what they promise.

What are the benefits of choosing a Passive House?

1. Energy Efficiency:

Passive Houses are extremely energy-efficient and require minimal heating. They achieve this by using advanced insulation materials, airtight construction, high-performance windows and doors, and a well-designed ventilation system. This results in significantly reduced energy consumption for heating and cooling, which can lead to substantial cost savings on energy bills over the long term.

2. Comfort:

Passive buildings are designed, not just to be energy efficient, but with the comfort of their owners at the forefront.

Passive Houses provide excellent levels of indoor comfort by maintaining a consistent indoor temperature (20°) and providing excellent air quality. High levels of insulation and airtightness ensure warm surfaces, lack of draughts and comfortable temperatures during both winter (by preventing heat loss) and summer (by limiting overheating). Additionally, with controlled mechanical ventilation systems with heat recovery a constant supply of fresh, filtered air is supplied, improving indoor air quality.

3. Health Benefits:

The emphasis on fresh air and balanced humidity levels contributes to a healthier indoor environment. This can reduce the risk of mold growth, dust mites, and other allergens, which are common in poorly ventilated homes. Improved air quality also has long-term health benefits.

4. Renewable energy

Passive Houses are very energy efficient. This means that a high proportion of their energy demand can be satisfied by renewable energy sources which, in ordinary, ‘inefficient’ houses would have minimal effect.

5. Environmental Benefits:

Passive Houses have a significantly lower carbon footprint compared to traditional homes. By reducing the energy required for heating and cooling, they contribute to lower operational carbon emissions. This is essential for combating climate change and reducing a household’s environmental impact.

6. Reduced Living Costs:

Passive Houses are cheaper to operate than conventional ones, with lower utility bills and fewer maintenance expenses.

While the initial construction costs of a Passive House may be higher due to the specialized materials and design, the long-term savings on energy bills often outweigh these costs. Over time, homeowners can recoup their investment and enjoy reduced living costs.

7. Comfortable Living Environment:

Passive Houses provide a consistent and comfortable indoor environment throughout the year. Residents experience fewer temperature variations, which can lead to a more pleasant and stress-free living experience.

8. More Durable Building:

Passive Houses are robust and long lasting making them more resilient in extreme weather conditions, as their efficient insulation and airtightness can help maintain a comfortable indoor temperature during power outages or severe weather events.  The filtered fresh air systems can cope with intense outdoor pollution events and maintain healthy air inside. Their robust building envelopes can weather intense storms. Their very low energy consumption means a modest solar array and energy storage system can power Passive House buildings when grid systems fail.

9. High Quality

Traditional construction and other green building certifications suffer from the “Performance Gap”, the lack of correlation between predicted thermal energy performance and actual performance once occupied. When you create a Passive House, you know what performance to expect, and the constructed building will perform as designed.

Thanks to their well-insulated envelopes and reduced risk of condensation, Passive Houses are more durable and require less maintenance than conventional buildings.

10. Uncomplicated

Passive Houses don’t require user manuals to operate.  The benefits such as pleasant temperatures, no draughts, and constant fresh air are the result of the design, not lots of complicated technology.

FREQUENTLY ASKED QUESTIONS

Are Passive Houses complicated, high-tech buildings?

No. A Passive House utilises higher quality versions of the same building concepts and components that are used in typical traditionally constructed houses. The ventilation system, is user-friendly and easy to operate with fewer controls than a typical television. Passive House technology is so simple, there’s no need to hire someone to perform annual air filter changes; you can do it yourself.

How does Passivhaus construction prevent moisture damage?

Passive Houses use airtight construction and thick insulation to maintain even indoor temperatures at around 20°C throughout, thus preventing condensation and mould growth. Airtight construction also prevents leaks through which moist air can enter the building envelope.

Can you open windows in a Passive House?

Passive House occupants may open windows whenever they want. The beauty of Passive House design, however, is that they don’t have to. A Passive House is continuously supplied with fresh air via the ventilation system, which does a far better job of consistently bringing fresh air in than simply opening the windows ever could.

Is the ventilation system noisy?

The ventilation system itself is housed in a very well insulated and airtight cabinet which is normally positioned in a utility room. The noise from the fans is no greater than that from a modern fridge. The ducting is fitted with what are referred to as ‘attenuators’ and combined with acoustic insulation, which reduce the sound of air passing through the system. In bedrooms, if designed correctly and properly fitted, air passing through the system should be barely audible at normal flow rates.

Does a Passive House need a conventional central heating system?

Passive Houses are designed to minimize the need for space heating, but they may still require a small heating system for extreme weather conditions. The goal is to maintain a comfortable indoor temperature primarily through passive means such as insulation, airtight construction and maximising solar gain, However some form of supplementary heating may be still necessary, especially on the coldest days’ to ensure occupants’ comfort. A Passive House may require as little as 3kW of heat at the coldest time of year whereas a conventional oil boiler produces around 20kW for example.

Does my Passive House need radiators or underfloor heating?

It is usual to find some method of heating in a Passive House. The type of system depends on the comfort levels the occupants would expect on the coldest days.

The choice between radiators and underfloor heating will depend on your specific requirements, budget, and personal preferences.

Will a Passive House be more expensive?

Passive House buildings are cheaper to operate than conventional ones, with lower utility bills and fewer maintenance expenses.

While the upfront construction cost of Passive House buildings is usually slightly higher (approx. 8-10% on average), this is due to the use of superior building envelopes and higher build quality.  The additional upfront investment is routinely offset by savings in running costs over the life of the building (heating bills are typically up to 90% less). 

Many homeowners and builders view Passive House construction as a worthwhile investment due to the long-term benefits in terms of energy efficiency, comfort, and sustainability.