Are passive houses worth it in the UK?
Passive houses, known for their exceptional energy efficiency and minimal environmental impact, are gaining attention in the construction industry. The basic concept of the Passivhaus standard is rigorous design and very high build quality to substantially reduce energy requirements for heating and cooling.
But are these houses worth the investment in the UK? Let’s explore the pros, cons, and some other options to determine if passive houses are the best choice in the British climate.
The principles of Passivhaus. See: The Passive House Institute
What makes a house a passive house?
Passive houses are designed and built to very high standards, employing five principles to ensure optimal energy efficiency:
high levels of insulation: very thick insulation is used in walls, roofs, and floors to minimise heat loss;
high-quality windows: triple-glazed windows with insulated frames reduce heat loss and prevent convection currents (and thus draughts);
ventilation system: mechanical ventilation with heat recovery (MVHR) ensures high air quality and eliminates condensation without significant heat loss;
airtight construction: this prevents drafts and heat leakage, contributing to consistent internal temperatures and comfort; and
minimising ‘thermal bridges’ that is, anything in the structural design or build process that breaks the insulation layer and can thus transmit heat through it.
In consequence, a passive house has minimal requirements for active heating and cooling; rather, it relies on both the passive use of the sun and a much-reduced loss of the heat that’s created by people and equipment inside buildings. This ensures thermal comfort in cold weather and, with shading and ventilation techniques as well as the insulation keeping external heat out, coolness in hot weather. (Both effects are enhanced by high levels of airtightness and high-performance glazing.)
The upsides of passive houses
Energy efficiency: remarkably less energy is needed for heating and cooling, leading to very substantially reduced utility bills and a lower environmental impact.
Superior indoor comfort: consistent temperatures throughout and controlled ventilation ensure a comfortable, completely fresh living environment all the time.
Environmental benefits: a much reduced carbon footprint due to minimal energy requirements.
Cost savings: Although initial design and some construction costs are slightly higher, savings on energy bills offset this, especially as energy costs continue to rise.
Exploring the downsides
Slightly higher initial costs
Designing and building a passive house usually involves slightly higher initial costs. You can find out more details in the section Does building a Passivhaus cost more? but, in brief, these extra costs are likely to include (i) additional design work to ensure compliance with the Passivhaus standard; (ii) greater levels of insulation; (iii) triple-glazed windows; and (iv) mechanical ventilation heat recovery system (which will be needed in any building with high levels of air-tightness).
Against this, your heating system installation costs will be much lower – you won’t need a central heating system. (In our passive house, for example, we have underfloor heating pipes below just 25% of the floor area: hall, boot room and the three en-suite bathrooms only, and no radiators; and the heating system rarely needs to come on.)
Expertise and construction challenges
Designing a passive house requires specialised knowledge. Building one requires attention to detail and greater care than is perhaps found in some new-build houses. This may lead to slightly higher labour costs.
Adaptation/retrofitting to the Passivhaus standard
Converting existing homes to the Passivhaus standard is quite possible but somewhat disruptive and, we suggest, requires expert advice.
Design flexibility
Passive houses can be built to almost any design and can be constructed of almost any material. The restrictions mostly concern balancing what you want with limits on space heating defined in the Passivhaus standard. Fortunately, the Passive House Planning Package enables modelling of all aspects so you can see what’s possible and what can be adjusted to enable different features.
Perhaps the only significant limitation is that, once built, it’s more difficult to extend a passive house. Principally, this is because to do so would breach the house’s airtightness and insulation which would require reinstating if Passivhaus performance were to be maintained.
Do passive houses smell?
Yes they do – of fresh, filtered air everywhere and all of the time! This is because the mechanical ventilation heat recovery system (MVHR) in a passive house continuously extracts air from the kitchen, bathrooms and toilets and, similarly, provides a constant supply of 100% fresh air to the house. We liken this to having a window open in every room but without draughts or heat loss. And because of the way passive houses work, you’ll be able to have open windows earlier in the year and keep them open later in the year than your neighbours will.
Another benefit of the ventilation system is that the smell of grilling kippers, spicy foods or anything else is quickly removed from the kitchen, as is steam from cooking and any slight misting of bathroom mirrors if you have a shower. This also means that condensation is a thing of the past: the ventilation system ensures that the relative humidity of the air in the house stays within the optimal range for the majority of the time (find out more in the section Relative humidity and condensation)
A Passivhaus MVHR unit. The large, heavily insulated, black ducts on the left are the fresh air inlet (above) and exhaust air outlet (below) of the house’s ventilation system. To the right is the house’s ground source heat pump. The MVHR unit is often situated out of site in a plant room.
This picture was taken from the Oakwright’s In the Frame video series
Are passive houses worth it?
Based on our experience, and that of others, the answer to this is unequivocally yes! This is because a passive house provides unparalleled internal comfort and tranquillity whatever the weather or time of year as well as minute heating bills. You will get both of these benefits from the outset.
The high quality of the design and build of a passive house, and, especially, the lack of condensation (principally because of a lack of cold spots due to excellent insulation, triple-glazing and a complete absence of draughts, and the continual use of a mechanical ventilation system) is likely to reduce maintenance and repair costs as well as prolong the life of the building.
In addition, the minimal need for radiators (if any) means that there is more wall space and thus greater flexibility for furniture layouts, and triple glazing means you can sit right up against the windows even when it’s really cold outside, so there is more usable floor space.
In terms of a financial return on investment, this will depend on both energy and property prices and may take a longer time to achieve. But whilst our initial interest in building a Passivhaus was the prospect of lower heating bills, now consider the excellent year-round indoor comfort and freshness to be the main benefit — the tiny heating bills are a welcome bonus!
Are there alternatives to the passive house standard?
The Passivhaus approach has been described as the gold standard for building energy efficiency, and the Scottish government plans to make a Scottish equivalent of the Passivhaus standard mandatory for all new homes from the end of 2024.
All new buildings in England are required to be designed and built to meet (or exceed) current building regulations, which have much lower requirements for energy efficiency. However, there are also additional, higher, standards for new buildings which are optional. For example, the government introduced the Code for Sustainable Homes in 2007: a set of sustainable design principles and performance targets for different aspects of the construction process. This was withdrawn in 2015 and replaced by new national technical standards.
BREEAM (Building Research Establishment Environmental Assessment Method) is another standard to consider. This covers a wider range of sustainability considerations than the Passivhaus standard: it measures a building's environmental impact across ten categories, including energy, water, waste, pollution, transport, and ecology, but does not necessarily guarantee the Passivhaus performance.
Some people have chosen to build to ‘near’ Passivhaus standards, for example with lower levels of insulation and only using double glazing. This approach is likely to reduce energy costs, albeit by a smaller amount. But, importantly, if designing and building a house with a high level of airtightness (which is a key aspect of energy efficiency) then, we suggest, it is vital to consider installing a properly designed mechanical ventilation system to remove the risk of condensation developing within the building’s fabric which could risk structural failure.
We think it worth reiterating the benefit of using the Passive House Planning Package as part of the design process of your house. Described in more detail in another post, this will enable you to avoid over-engineering and to have a home that – if then built as designed – will do exactly what it says on the tin.
Experience the Passivhaus difference
You can experience the passive house difference at Woodlands Malvern B&B and we’d be pleased to discuss our experience of designing, building and living in a certified Passivhaus with you.