Passive Houses: A Worthwhile Investment in 2024?

By David Tait

Editorial Manager

What is a passive house and what can it do for you? The housing crisis over recent years in Ireland has pushed the Irish housing market to ever-expanding new limits. However, are we making sure all new housing is an investment in our future, or digging ourselves deeper into a pit of carbon debt?

What Is a Passive House?

A passive house (also called by the German name Passivhaus) is not actually a type of house, it’s a standard for energy efficiency. Passive houses typically have the following attributes:

• Ultra-low energy construction material buildings
• Require minimum energy in order to stay warm in the winter.
• Require minimum energy to stay cool in the summer.

As a housing standard and not an actual type of housing, passive house design should be integrated with architectural processes when building houses. 

Due to the intensive nature of the changes required to make a house of passive house standards, it is normally applied to new builds, although some older houses have also been successfully refurbished a la passive house style.

The majority of passive houses have been built in Germany, Austria, and Scandinavian countries, although their popularity throughout Europe is growing. Passive house standards as we know them originated in 1988 as part of a collaboration between Bo Adamson from Swedish University Lund, and Wolfgang Feist from the German Institute for Housing and the Environment.

Since then, it has been developed and researched further. The first examples of the passive house standard were constructed in Germany in 1990. To date, thousands of houses incorporating passive house design have been built, estimated at more than 25,000 in 2010. It was not until 2010 that a refurbished house was awarded the passive house standard.

Ireland’s dance with passive housing began in 2005, built by Tomás O’Leary, and named “Out of the Blue”. According to the Passive House Association, to date, only 45 passive houses have been registered in Ireland.

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How Do Passive Houses Work?

Passive houses try to improve the energy efficiency of buildings. The main areas they focus on include the following:

1. Airtightness
   Passive house standards mean that buildings must be much more airtight than the norm. A building being airtight means that it is much more likely to maintain an intermediate temperature, and not be influenced so much by external conditions. Passive houses increase their level of airtightness through the use of air barriers and heat exchangers.
2. Lighting and electrical devices
   Natural light is maximised in passive houses to reduce the amount of energy expended on lighting. For any areas of the house without natural light, at nighttime, and on those grey dark wintry days, sustainable lighting can be used. Sustainable lighting normally consists of low voltage bulbs, led lamps etc. Solar power can also be used to drive lighting systems.
3. Space heating
   In passive houses, solar energy is maximised as much as possible on the surface of the house in winter. “Waste” heat from lighting and electrical appliances and body heat from inhabitants also add to the heat value of the house, but sometimes a heating top-up is still needed. That’s where space heating comes in. Space heating can include a heating element incorporated into the ventilation system. This heating element could then be powered by solar thermal energy to make the house run 100% green.
4. Ventilation
   Passive houses are designed to allow a natural exchange between the air inside with the outside air. When the air outside is not at a favourable temperature, for example during wintertime, then a heat recovery ventilation system is used. Interestingly, a feature of some modern passive houses nowadays is earth warming tubes. These tubes are buried in the garden and are used to preheat or precool air going into the ventilation system.
5. Windows
   Regular double-glazed windows won’t do for passive houses - in order to reduce heat loss in winter and heat gain in summer, windows need to be extremely well insulated. This normally translates to triple pane glazed windows with special coatings and gas between the different panes.

What Standards Does a Passive House Need To Meet?

Passive house standards require several requirements in order for a building to be deemed a passive house. These requirements include:

• Limits on Heating and Cooling
  The heating and cooling demand of the building must not exceed 15 kWh/m2. So if you have a small 200m2 semi-detached house, for example, you shouldn’t use more than 3000 kWh per year. In Ireland, the average gas usage per year is at around 11,000 kWh, so this represents a big drop.
• Consumption Limits
  Total energy consumption (including electricity) must not be over 60kWh/m2 per year. If we use the same example again of a semi-detached 200m2 house, the average consumption should be 11,000 kWh of gas and 4,000 kWh electricity a year, so 15,000 kWh. A passive house should not use more than 12,000kWh maximum.
• Airtightness Restrictions
  Air must not exit the building at a rate of more than 0.6 times the house volume per hour. A blower door ( a machine to test the airtightness of a building) can and should be used to evaluate whether the house complies with this standard.

As you can see, these are some pretty specific standards you are unlikely to achieve with a bit of duct tape and some insulation. If a building meets these standards, it should, in theory, then be able to dispense with a regular heating system. 

They will still need a heating top-up though, so most passive house buildings use heat recovery systems and also heat the air passing through the ducts when needed.

Are Passive Houses Expensive?

You would think so, but actually bringing a building up to passive house standards, if done well and carefully, shouldn't mean the house is more expensive than a regular house. The reason for this is that the funding usually budgeted for installing a heating system can usually be used to bring about passive house modifications.

Traditionally, passive houses have been viewed as nice, but expensive, with estimates of their price over 25% more expensive than a “normal” house. However, jumps in technology and production over the last few decades have steadily driven down the difference to around 0%.

There is no consistent metric to measure pricing against, as passive house standards can differ from country to country and year to year. The easiest way to see if that new build you have your eye on could be made passive on the cheap is to analyse the following factors as extra costs:

• Extra components and materials (for insulation, windows, air ducts)
• Extra technology (solar panels, heat exchangers etc.)

Then check if you can take away these possible deductions from your building costs:

• Use single skin blockwork and external insulation instead of the usual masonry double skin.
• A standard heating system (small space heating units for passive house constructions typically cost far less than central heating systems).

There is also the fact that initial investment aside, the lifetime costs for maintaining a passive house, and a huge - or total- reduction in energy costs, represent some huge savings.

All things being equal, if you can keep the building passive house costs down, then you’re definitely making a sound investment that will more than pay for itself in the long run.

In addition, there are several grants available for features of passive houses in Ireland. Finally, particularly for those who are buying to rent or investing in social housing, there is the fact that a passive house will enable your future tenants to avoid fuel poverty. 

An investment in a passive house building also future-proofs it against rising energy costs. You should also check out the the array of solar panel grants that are also available from the SEAI.

How Are Passive Houses Certified?

Under the Energy Performance of Buildings Directive from May 2010, all new builds must be “nearly” zero energy, or built to passive house standard, by 31st December 2020. We think the EU may have been a bit ambitious with this target but we applaud the effort.

In Ireland, there is no “official” passive house certification body. There is, however, a passive house association of Ireland which organises training to ensure its members are au fait with the latest passive house standards.

The Royal Institute of the Architects of Ireland also provides a certified European passive house designer course for their members, accredited by the acclaimed Passivhaus Institut.

If you’d rather go your own route, just make sure to ask plenty of pertinent questions about the architectural firm you wish to contract. In particular, enquire as to which particular passive house standards they adhere to.

How Much Are Passive Houses in Ireland?

There are several companies dedicated to building passive homes in Ireland.

Ecohouse has six beautiful designs ready, ranging from a tiny house to a contemporary two-storey, with an option to self-build where they only provide you with the structure and plans, or a full build. A self-build passive house will cost you €750 per m2, while a full build is €2000 per m2.

Viking house is a passive house construction company which specialises in timber builds and solar roofs.

Scandinavian homes, located in Galway, provide prefab low-energy and passive timber frame homes and operate all over the country. There are some very affordable options on their product listing, such as a 78m2 passive house for around €105,000.

If you're just looking at the cost of upgrading your energy efficiency, you should check out out solar panel costs guide to see how much it might be worth investing in.

Can I Refurbish a Home Into a Passive House?

So far, we have looked at some of the standards that need to be met in order to call a house a passive house. The good news is that, you do not need to buy a new home for it to meet those standards, you can also refurbish an existing home to be more energy efficient.

In fact, the SEAI has a series of grants available to entice people to upgrade their homes with some of the passive house standards. Get a certified contractor to give you a free estimate and see how much you can save in the long run with new windows and doors, better insulation, or a better home-heating system. Be sure to check other environmentally-friendly related schemes such as:

• Electric vehicle grants
• Solar panel installation
• Heat pumps