environmental & green building news, taos, new mexico

I’ve been seeing a lot of articles about Passive Houses (or Passivhaus) in the news lately. I’m glad, because this is the construction technique of the future, reducing utility bills by 90%! As energy prices rise, buildings will have to be more efficient. There is no excuse to not build a green home, and the Passivhaus is the best choice.

The Passivhaus, a performance based building standard, was developed in the late 1980s in Germany by Dr. Wolfgang Feist and Bo Adamson. The first passivhaus was built in Darmstadt, and Dr. Feist subsequently founded the Passivhaus Institut in 1996. Today there are approximately 15,000 residential and commercial buildings built to this standard in Europe.

Construction features of a Passivhaus are:

> Compact size – 50 square meters (approx 538 sq ft) per person
> Super insulation of floors, walls and ceilings
> Air-tight envelope with no thermal bridging
> High-performance doors and triple glazed, insulated frame windows
> Heat recovery ventilation (HRV)
> Passive solar
> HERS score 20-30
> PHPP Certification (Passivhaus Planning Package)
> Space heating must be no more than 15 kWh/sq m (4.75 kBtu/sq ft)
> Overall energy use must be no more than 120 kWh/sq m (38 kBtu/sq ft)
> HRV air exchanges must be 0.6 or less per hour at a pressure rating of 50 Pascals.

Benefits:

> Improved indoor air quality
> Increased physical comfort
> 90% energy reduction
> Minimal conventional heating system
> Suitable for retrofits
> Affordable

The point of passivhaus construction is to minimize energy loss by restricting air flow into and out of the building. The building stays warm in winter and cool in summer. There is not one passivhaus design. Feist says that style does not matter, as long as the efficiency and air circulation goals are achieved.

> The envelope is super-insulated, up to 16″ beneath the slab and in exterior walls (R 60-70). Strawbale, SIPs and ICFs (insulated concrete forms) or Rastra are suitable for passivhaus construction.

> Ceiling insulation of dense-pack fiberglass, cellulose or spray foam has an R value anywhere between R 60-100.

> The triple-glazed windows have a very low U-factor of 0.14. Some in Germany are as low as 0.17. The U-factor rating of the National Fenestration Rating Council (NFRC): the lower the number, the more efficient the window, based on the glass, frame and spacer material.

> Points where indoor materials meet the outdoors (thermal bridging) are sealed, as are all points where air can move. A blower door test is run several times during construction to test for air leakage before the building is completely closed up and finished.

> Once a building is air-tight, it needs ventilation. A heat recovery ventilator (HRV) exchanges indoor air with outdoor air with minimal heat loss. Most people will crack a window to get some fresh air in winter, and what happens? The heat goes out the window! An HRV reduces that type of heat loss while keeping the indoor air fresh and healthy to breathe.

Because passivhaus is performance-based, the buildings are montiored after final construction. The CEPHEUS project monitored 250 passivhaus’s in the EU, and their results showed an energy reduction of 90% on average.

I have heard varying estimates of the extra cost to build a passivhaus with a range of 5-10%. This is offset quickly with the huge energy savings. The payback period depends on each individual home’s energy use. The best thing to do is begin to conserve energy before building or retrofitting with passivhaus standards.

Passivhaus construction is not catching on quickly in the US, but the Passive House Institute US, based in Urbana, Illinois, is trying to change that. The Director, Katrina Klingenberg, a German architect, built her own passivhaus in 2002. PHIUS is authorized by the Passivhaus Institut in Darmstadt as the official Certifier of Passive Houses in the US, designing and certifying homes and training designers and consultants.

In an email, Dr. Feist told me that the only thing keeping the passivhaus becoming more popular is education.

‘There is no limit to growth for Passive Houses – only the availability of specific components (which can be produced regionally in the EU as well as in America) and the distribution of the know how. This is indeed the bottleneck at the moment. But education programmes are already available – so it will be overcome.’

The European Commission has already mandated that all new buildings in the EU be ‘nearly zero energy’ after 2020. Feist says, ‘The Passive House is the prototype of a “nearly zero energy building.” Seen this way, in 2020 the fraction of Passive Houses of all new built will be 100% in that part of the world.’

The addition of renewables (solar, wind) can make a passivhaus a net-zero home, but the energy creation and consumption of a passivhaus is meant to be just that – passive. To me, that is a gentler way to live, and there are no moving parts to maintain. A 90% reduction in the energy consumption of a passivhaus is good enough for me!

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