Passivhaus or Passive Fit?
- Building Design Expert
- 5 years ago
Looking through a misty condensation covered window from the outside we might forgive the public at large for taking their bats home en masse at the mention of air-tight, highly insulated, renewably fuelled, sustainably constructed, zero carboned, not to mention consummately ‘Green’ Building. I think I would too, only, hold on, it’s my job to try and make sense of all this.
Code for Sustainable Homes (C4SH), BREEAM and Passivhaus are the current popular ‘Green’ standards by which we live and breath in the building design industry. By comparison BREEAM and C4SH are similar versions of each other applied to the commercial and domestic sectors respectively. One might mistake these assessment methods as the somewhat free thinkers of the trio, with concentration on environmental impact of the building both under construction and in use. It gives no dramatic underline to air tightness, or super-insulation. But instead takes a step back and gives an overall holistic assessment based upon:
- Energy and water usage,
- Health and well being potential within the internal building environment,
- Resultant pollution,
- Sustainability of construction materials
- Ecology and management processes
They both offer assessment on a points based scoring system that naively presents itself as ‘Good’, Very Good’, ‘Excellent’ and ‘Outstanding’ for BREEAM, and grades 3, 4, 5 and 6 for C4SH – grade 6 representing an achievement of ‘zero carbon’. But is it really ‘Zero’ – read on.
Lets look at the points system for BREEAM scoring:
- Unclassified under 30
- Pass 30+
- Good 45+
- Very Good 55+
- Excellent 70+
- Outstanding 85+
Looking at a pinnacle score of 100, a ‘Very Good’ at 55 seems coincident with our much criticised ‘A’ level grades at around a ‘C’ as an average. Certainly nothing to shout about, and ‘Very Good’ might be over-egging the reality by a degree or two.
What I struggle to get my head around in both BREEAM and C4SH are things like the reward of points for cycle storage, and provision of a ‘home office’. Both laudable green and sometimes sustainable principles, but the policing of inclusion is very much in doubt. Electrical usage is based on assumption, as is the installation of automatic system controls that you might need an ‘A’ level grade C or above to decipher the operating manual. The assessment is spurious at best and too often subjective. Are there points for the architect putting the correct scale on the drawings? Come on please, this sort of approach lets down what needs to be a rock solid system.
We are dealing with the saving of resources – energy, water, and the minimisation of environmental impact. This is Building Science and should be treated as such. Instead building designers are allowed to shoe horn in an extra cycle rack that could conceivably take the building score from ‘Very Good’ to ‘Excellent’. No, sorry, not good enough.
Is ‘Passivhaus’ any better?
Remember “vorsprung durch technik”? Loosely translated it means “progress through technology” – and you will see why.
Also promoted under the umbrella of the BRE, Passivhaus standard is reliant upon a more intense focus to reduce, and preferably negate the need for space heating and cooling, such that the internal building environment remains constant (within prescribed parameters) all year round.
Passivhaus was developed by a German and Swedish professor, in Germany in 1991. The houses were constructed in Germany during 1993 and we know, thanks to resolute continued German monitoring that these buildings continue to use less than 10 kWh/m2. Those fortunate householders enjoy 90% off their energy bills still; proof, if needed that building performance is not at the mercy of time. We continue to watch and learn.
Passivhaus has been defined as: “A Passivhaus is a building, for which thermal comfort can be achieved solely by post-heating or post-cooling of the fresh air mass, which is required to achieve sufficient indoor air quality conditions – without the need for additional recirculation of air.”
The classic Passivhaus design requires no artificial heating or cooling. It is purposefully orientated to mitigate against the effects of solar gain, and has it’s window and door openings carefully sized and positioned to strategic elevations to effect this design ethos. Air tightness is also 90% better than the current Building Regulations require. The building envelope is highly insulated, and ventilation is strictly controlled.
Passivhaus is a ‘fabric first’ solution to building design and can equally be applied to private homes, or commercial properties. The primary difference to BREEAM and C4SH is its environmental friendliness, not by design, but by default. Using one tenth the energy in a continually stable environment has got to float most peoples boats. The biggest draw back is that if you throw in a free cycle rack it doesn’t get any better. That is not to say that BREEAM is not able to do super-insulation, but it’s just not at its heart. It tends to take a ‘Jack of all trades’ approach, where Passivhaus is quite focused.
So what can we take from all this?
BREEAM and C4SH we are stuck with to a large extent because these are the standards of the day, and the few recognisable routes to the governments ‘zero carbon’ goal. They probably tick the ‘Sustainability’ box much more positively than Passivhaus with rewards given for appropriate materials specification, in addition to the resultant built environment and ecology.
Passivhaus offers an ‘end game’ with little credit as to how you get there. More responsible building designers will undoubtedly take elements of BREEAM and C4SH design and specification, and supplant them into the mix where possible. But not at the risk of their super energy efficient building that provides a BREEAM ‘Excellent’ internal environment by default.
The oldest Passivhaus is just under twenty and still performs today as well as it did when first built. That’s remarkable, but Passivhaus buildings carry their own design quirks, and it’s not for everyone.
It’s an interesting street down which to travel. Have a look at all the building types and by the time you have reached the end you can decide whether you want a Passivhaus or a Passive Fit?
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