Total Construction Duration to date

Wednesday, 15 October 2014

Does PassiveHaus make sense?

Just a short update to showcase an article at Green Building Adviser that perfectly sums up the conclusions I made about the Passive House program and why I cancelled my plans to build to that standard.

The author of the article, found at www.greenbuildingadvisor.com/blogs/dept/musings/it-s-not-about-space-heating, tracked the actual energy use of several homes in Massachusetts and has determined that even a modest investment in insulation and air tightness (termed a pretty good house by Joe Lstiburek) is more than enough to reduce the heating and cooling loads to the point where it makes more sense to concentrate on plug and domestic hot water loads as is shown in the below graphic.


Extracted from http://www.greenbuildingadvisor.com/sites/default/files/images/Rosenbaum%20-%20Graph%20of%20Eliakims%20Way%20data%20copy.preview.jpg

The real world data monitoring has also shown that the assumptions made in the PHPP (the modelling system for PassiveHaus) are often wrong.  The author states, “PHPP assumes 6.6 gallons [25 liters] of hot water a day per person, but that’s not enough for normal Americans.”

I jumped on board the PassiveHaus train for about a year in the early design stages of my upcoming build.  It was easy to be swept up in the well polished program and fall in love with the projected savings.  But as I became better and better educated on building science, source energy, and embodied energy, I felt their were huge holes in the program.  The underlying principles of air tightness and thermal bridge free construction were sound, but in my view the chase for heating and cooling reductions bypassed the sweet spot where it made much more sense, from an embodied energy and a cost point of view, to look at on site production than further reduction. The biggest stumbling block was the claimed 10-15% added build cost to reach PH when in reality it is much closer to 200% on average when comparing to a code min house (which after all is what the majority of homes in North America are built to).

In the end I decided to build a "pretty good house" and will monitor energy loads once occupied and then model whether or not I reached the sweet spot between reduction and production.

Thanks for visiting.  For the current status of the build please visit http://www.theenclosure.ca/project-journal/

PS: For an excellent article on why  more insulation is not always better, read http://www.greenbuildingadvisor.com/blogs/dept/building-science/diminishing-returns-adding-insulation

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