Passive house technology has been around for more than a 100 years and is commonly used in Germany, Austria and some Scandinavian countries. But at the rate we’re going it could be another 100 years before we see a real switch to passive building in the UK.
Houses built today in the UK will probably last for 70 to 100 years, so why are they not being built using old technology? The truth is, without strict legislation, house builders can remain focused on their bottom line.
What is a passive house?
A passive house is classified as using just 10% of the energy that a “normal” house uses. The energy requirement for a passive house is 15 kWh/(m²a), a traditional house requires 180 kWh/(m²a)
How is this achieved?
To design and build a passive house is not difficult. It is mostly a matter of common sense, good building practice and the use of the best building products available.
Below are some of the criteria required to build a passive house;-
- Good insulated walls (U-value 0.1 – 0.15 W/(m² K)
- Compact building design (surface to area volume)
- Minimum thermal bridging
- Excellent air-tightness
- Thermal efficient windows and doors
- Efficient heat recovery and ventilation system
- Positioning of the house in relation to the sun
- Green heating systems
How it works in practice
A draft free environment
Ever wondered why a house can feel draughty even though everything seems wind proofed? Sit next to a single glazed window on a cool day and you’ll sense a draft. This is because of the natural effect of heat rising and then falling as it cools. As warm air comes into contact with a window it is cooled which cause the then cooled air to drop which in turn pulls more air down in its wake. The resulting air movement is felt as a draught.
In a passive house construction all the exterior surfaces including walls, windows and doors are insulated to a very high standard. This helps to stabilise the internal temperature thus dramatically reducing the chilling effect of air movement.
Harness the sun’s energy
Losing more energy than they contribute, windows and doors are very often negative contributors to the flow of energy. This is opposite in a passive house. The windows and doors are so thermal efficient that there is a net gain of energy. Windows in particular, become the radiators in your house. In certain conditions solar-gain can be a problem, something to consider when designing a passive house.
Of course, it goes without saying that there are many other ways to capture the sun’s energy, such as, solar panels and ground source heat pumps. These areas though aren’t my specialty so I’ll not say too much other than it’s common sense that the more energy you can grab for free the more you’ll save over the long-term.
Fit the right windows – properly!
It’s not just a case of choosing passive house rated windows. Simple construction details, like how windows and doors are fitted into the fabric of the building are just as critical in achieving passive house status. Correct fitting will save hundreds of pounds without the need for additional investment over and above the cost of the windows.
At Broxwood we offer two types of passive house compatible windows and doors. Our standard product range is available in 0.7 u-value and for the highest quality and best u-value we offer the Hand Finished 0.6 u-value AlpineMax range.
The most critical part of the passive house is the ventilation system. As mentioned above your windows can capture an incredible amount of solar energy but there is also the potential for the temperature to rise too high in the room. To run an efficient passive house, you need to be able manage the heat distribution. This is done using a heat recovery and ventilation system. These systems not only utilise excess energy in the house they also refresh and regulate the air. A good quality will work equally well in the summer and winter by cooling in the air in the summer and warming the air in the winter.
So why don’t UK house builders all build Passive houses
Easy – they don’t have to! According to records from Germany and Austria, a passive house will cost on average 8 to 10% more to build than a traditional house. The major UK house builders are owned by shareholders who naturally expect growth and profits. Therefore, up until now, developers are more interested in creating the dream house for the highest possible return. And as recent figures show, house builders are still struggling.
So why spend an additional 8% if it can be avoided. But in a world where marketeers can sell ice to Eskimos, surely the promise of reduced energy bills for life is a marketeers dream. ‘Buy this house and save a minimum of £1500+ a year for life!’
My plea to house builders
I don’t want to suggest that house builders don’t care or that they aren’t already building some energy efficiency into houses but I believe they can voluntarily do so much more. It’s unlikely we’ll shift to every new house being passive but houses could be a lot more efficient than they are now. Every house built today that is not at least close to passive could continue consuming vast quantities of energy for the next 70-100 years.