Sunday, November 9, 2008

The future of housing

I'm yust back from the North American Passive House Conference in Duluth, Minnesota.  Redbeard recommended I should go and he was right.  It was a small conference but very good.  I thought the presenters represented the best thinking on sustainability, and the audience participants also had smart questions and comments.

Passive house is a super-insulation concept for buildings (which originated in the U.S. and Canada in response to the oil shocks of the 1970's) was formalized and so-named about 15 years ago in Germany, and is now reimported/revived in the U.S.   The key concept is that as you add more and more insulation and air tightness to a building, you can take more and more cost out of the heating system, therefore you can get dramatic (90%) reductions in heating and cooling energy for little extra cost - a true win, not just a tradeoff.  Or, to put it in my accustomed sarcastic and curmudgeonly terms, it is ridiculous to continue the stone-age practice of burning stuff to heat the house, now that we have so much better insulation...than in the stone age.

The Passive House Institute has set a Passive House Standard.  It is a performance-based standard which I think is focused on the right things.  Being German, it sets very stringent requirements for air-tightness, total annual heating and cooling energy per square foot of usable floor area, and total household energy use including all appliances.  They derive these allowances from a concept of per-person fair share of the earth's capacity to absorb greenhouse gases.  The Germans have about a ten-year lead and have thousands of buildings meeting this standard; in the U.S. there are only a few yet.

It's interesting (I'm sure you'll agree) to compare and contrast the stereotypical German Passivhaus, the two examples we toured in Duluth (the Isabella Eco-House and the Skyline House), and the HDT Eco-Cabin from which I am broadcasting here.

The big difference is that all three U.S. houses are considerably fancier.  All three are tricked out with solar water heat systems for both domestic hot water and space heating.  Two of the U.S. houses also will have solar electric systems.  Two also have attempts at long-term (seasonal) heat storage in the ground under the building.  Partly this is because of the harsher climate of Minnesota as compared to Germany, and partly because of lingering bias in the U.S. towards adding renewable sources of energy instead of efficiency measures.  The canonical German Passivhaus is a super-insulated, super-tight house with full time mechanical ventilation through a heat-recovery ventilator, and a small (1000 watt) electric heater also integrated into the ventilation system.  

The Isabella Eco-House:

The Skyline House:

Compared to these places our HDT cottage here is relatively modest, and uniquely intended from the start to be 100% solar.

There was also some great stuff on retrofitting existing houses, how to achieve deep reductions in energy use without breaking the bank.  Things like super-insulating only a portion of the house, or building a small super-insulated addition.

There was also a very interesting presentation on straw bale construction.  The presenters had basically given up on making the straw bales load-bearing, and had evolved basically to a double-walled wood frame house construction with straw bales as insulation.  They were even cutting the strings on the bales to eliminate the gaps between them, essentially turning the straw into a dense-pack insulation within a wood structure.


Anonymous said...

Considering that the ratio of new builds to existing structures will always be low I would like to see more information on how the existing structures can be improved for energy efficiency. To me - building new is less green than re-using old in smart ways. - any thoughts would be appreciated.

AK - Rochester NY

Correspondent said...

The classic literature on the subject is from 1981, The Super-Insulated Retrofit Book by Marshall and Argue. As far as I can tell, the deep energy retrofit is in its infancy yet. There has been only one retrofit to passive house standard in the US, and it was in Berkeley which is a very mild climate. It made the cover of Home Energy magazine. This magazine is basically for people in the Energy Star business. Energy Star is a very successful program which can achieve 20-30% energy savings in homes, mainly by air-sealing and furnace upgrades. The presenters at the Passive house conference made two points: that 30% is not good enough, and that doing only new builds is not fast enough because the housing stock turns over so slowly.