20 November, 2011

Passive House (PassivHaus Institut)

If you haven't heard of the "Passive House" movement or you just haven't heard what it means, I'll try to explain it best I can.  Concerns over the effects of housing heat exhaust to the climate and pollution brought about the desire to eliminate as much energy/fuel use as possible. 

The PassivHaus movement began in Germany during the mid-1990's and it is the fastest growing energy performance standard in the world with over 30,000 buildings built to date.  The PassivHaus ideal is simple; build a house that has excellent thermal performance (super-insulated), exceptional airtightness coupled with mechanical ventilation.  The building is heated by solar gain from windows and doors along with internal heat gain from people and electrical appliances. The summer cooling load is controlled by low-e coatings in the glass, window orientation and shading.  Any remaining heating or cooling demands are covered by a small heating source. Think of it as creating a livable thermos bottle, what is warm stays warm without using a heat source most of the time.  As Lloyd Alter of Treehugger.com says; "Forget Energy Star and LEED, green building is PassivHaus".

Graphics courtesy of PassivHaus Institit.
This approach to building design allows the architect to minimize the heating demand of  buildings, and may specify only a heated towel rail or small electric baseboard heater as the source of conventional heating. A mechanical Heat Recovery Ventilator (HRV) unit reduces indoor air pollution, by supplying fresh air which is filtered and heated by the warm exhaust passing through the HRV unit.  Triple pane windows and insulated doors, both with multiple weatherstripping sets are also required to bring the building into the standard.

A PassHaus buliding to the right and a conventional structure across the street. 

While it's much easier to build a new structure to this standard than try to bring an existing building into it, there are folks out there trying to do it.   Basically the insulation required to come near PassivHaus standard is R50 walls and floor (yes, floors), R70 ceiling or roof.  One method would have the interior of the house gutted before new inner walls can be constructed to provide ten-to-twelve inches of blown-in insulation space.  At a green building seminar I attended last year, one Cleveland manufacturer showed off a custom six-inch thick XPS (extruded polystyrene) panel with molded-in steel studs for fast setup.
A representative comes out and does measurements, wall panels are shop-constructed and brought to the site with electrical boxes mounted.  The existing wall gets blown-in insulation, the XPS panel is mounted over that. Spray foam makes the airseal at any joints.  Drywall is screwed to the embedded steel studs.

Getting the house airtight enough seems the hardest thing to do, but finding the doors and windows that meet the performance requirement is still difficult in the US.  Read 'limited availability' as much higher cost.  I estimate that to bring my 1925 Colonial-style (1400 sq-ft) home to near PassivHaus standards, would cost approximately 55-to-70 thousand USD.  Though I'm sure that as more houses are brought into the PassivHaus standard, the prices of materials and services will drop.