Passivhaus is one of the terms out there in eco-green-sustaintable building land. It may look like its spelled wrong but that’s because its originally from Germany. It represents a very strict and high standard of energy efficiency in a building. It isn’t (yet) an official requirement or standard but it is gathering momentum as an unspoken standard.
There are three complementary core ideas behind the idea of a Passivhaus:
- Complete and thorough thermal insulation of the house which prevents conductivity of heat from the inside-out or the outside-in.
- Complete air-tightness which prevents exchange of heat through air leaks (windows, doors, pipes, chimneys … every opening needs to be sealed!).
- An efficient ventilation system that both exchanges air (from the outside and the otherwise airtight house) and does so without losing heat.
This is one of those images that is better then a thousand words. The apartment building on the left is standard/traditional building while the apartment building on the right is built according to the Passivhaus standard. That’s the bottom line of Passivhaus – keeping the heat from escaping means you need to expend less energy to heat the inside.
I have come across Passivhaus numerous times in recent weeks and my recurring personal impression is that it is too extreme:
- It seems like more of an academic indulgence then a practical construction practice.
- It’s objective and success is measured in a single number – the amount of energy needed to heat a square-meter of space.
- It demands rigorous builing disciplines which require uncompromised excellence in construction.
- It demands the use of specialized insulation materials which can be expensive (especially if you consider the ecological foot-print involved in manufacturing them).
- It creates a house that demands constant attention, maintenance and proper use by its residents (every window opened and every hole drilled in the wall is a potential energy hazard).
All of which results in a delicately balanced system: if it isn’t absolutely sealed, perfectly ventilated by a carefully installed system and properly used it just won’t work. There is no room for error. This maybe OK in a scientific experiment but not so for life, nature and people.
In any case it doesn’t feel right for us: we have a limited budget, average construction capabilities, standard building materials, etc. We are going to do the best that we can with what we have. It’s an 80/20 kind of thing – where 20% of the effort takes you 80% of the way you need to go and it would take another 80% of effort to go the rest of the way. We’re aiming for a good middleground – pushing the limits of what we have – but that, by definition, is not enough to go for 100%. Passivhaus is uncompromising, but we live in a reality which demands compromise.
“A passivehouse is cost-effective when the combined capitalized costs (construction, including design and installed equipment, plus operating costs for 30 years) do not exceed those of an average new home.”
I am hesitant to relate to this statement as that may give it unwarranted legitimacy – cost is just too narrow a perspective to view ecological housing. But if I do meet it head on, as is, I would say that it sets its sights much too low. I hope to build a house where the combined capitalized costs are much lower then those of a new average home (whatever that is). I also hope to build a house who’s qualitative effects (both for us and others) far outway it’s economic effects.
Maybe Passivhaus is, for the time being, a high-end building experiment? Maybe in time it will spawn accessible, affordable and feasible techniques, solutions, technologies, practices … that can become a defacto standard that simply makes sense to follow? For now, it is out of touch with us and our needs.
Having said all that exploring Passivhaus has brought to my attention a factor I had not taken into consideration in all of my energy research: Indoor Air Quality. I have been following a very basic intuition: “generate heat” in trying to solve a problem we’ve been having for many winters: “being cold”. Most of my attention has been on how to preserve and generate heat (space and water) effectively.
I had not given any thought to one of the central themes of Passivhaus: quality of air. Quality of air (assuming there is good ventilation) is strongly effected by humidity … and humidity effects the overal experience of temperature … cold is much colder when humidity is too low and heat is much hotter when humidity is too high. I have experienced the effects of humidity in warm and cold temperatures in Israel and I have seen it (as accumulated moisture and mildew) in almost all Romanian homes I have visited.
I don’t know yet enough about ventillation and humidity.
One of the much praised qualities of hemp masonry is it’s breathability. It seems to have a natural tendency to absorb and expel unneeded moisture. I don’t yet have enough information on the overall effects of hemp on moisture, ventilation or quality of air indoors – but I do have a good feeling about the effects of hemp!
Following are some of the resources I came across and consumed in trying to understand Passivhaus:
- BRE – Passivehaus Primer – which I found at Passivhaus UK
- Wikipedia entry for Mechnical Ventilation Heat Recovery (MVHR) systems
- Blog post about MVHR’s by Mark Brinkley
- Forum debate about MHVR’s at Green Building Forum
- Blog post about a Passivhaus built in Cardiff at a staggering cost of £1,400 per square meter
- Wikipedia entry for Passivhaus
- Passivhaus Institue (which was quoted above)
- Some Passivhaus built houses