In praise of the dumb home: A Passivhaus 25 years later

Passivhaus in Darmstadt
CC BY 2.0 Passivhaus Institut via Wikipedia

There is not much that can go wrong in such a simple concept. That's really smart.

A few years ago I wrote In praise of the dumb home, a paean to Passivhaus and a rejection of fancy complicated smart technologies. I wrote:

Then there is the Passivhaus, or Passive House. It's pretty dumb. A Nest thermostat probably wouldn't do much good there because with 18" of insulation, and careful placement of high quality windows, you barely need to heat or cool it at all. A smart thermostat is going to be bored stupid.

Solar house is complicated© Peter van Dresser, 1977

Unlike the fancy solar houses of the seventies, a Passivhaus design is pretty simple, dependable, and durable. Exactly how durable has just been demonstrated by Dr. Wolfgang Feist, Rainer Pfluger & Wolfgang Hasper in their study Durability of building fabric components and ventilation systems in passive houses.

Dr. FeistDr. Wolfgang Feist in Vienna/ Lloyd Alter/CC BY 2.0

They examined the first Passivhaus dwelling, Dr. Feist's own, built in 1990 in Darmstadt, Germany. The house was a test bed and has been monitored ever since.

The house is a very straightforward design, a simple box with masonry walls, wrapped with 11 inches of exterior foam insulation and a mineral plaster stucco exterior, known as EIFS. The wall has held up rather well:

A visual inspection of the fa├žade shows that the exterior surface is intact everywhere, though it has turned grey and has been stained (vandalism) in spots. An expert assessment found that the exterior plaster does not currently need to be renewed; a new coating, with a diffusion-open, waterproof silicate paint, is possible for aesthetic reasons, but not yet necessary.

Credit for this can go in part to the simple design; there are no jogs or bumps or places that can catch water. In all seriousness, It is a dumb box.

Then there is the roof, which has also lasted 25 years, which I would never have expected.

roof design© Dr. Wolfgang Feist et al

The building code required green roofs in the area. The grass roof rests upon chipboard supported by I-beams (Fig. 4). The axial distance between the beams is 1.08 m. With an insulation thickness of 445 mm, using blown-in mineral wool, the roof has a U value below 0.1 W/ (m2K). If a non-ventilated roof is used, the design must ensure that moisture does not build up. Here, PE film on the interior fulfils this purpose.

I would have thought this was terrible practice, that polyethylene vapour barriers are useless, that a non-ventilated roof would just end up with a bunch of soggy insulation. But no; it has stood the test of 25 years. It may well be that the climate is more moderate, or the green roof on top kept it a bit warmer, or they just got really lucky with their vapour barrier. Or maybe our science was wrong all along.

UPDATES: Dr. Feist tweets:

Even the windows have hung together after all this time; I have often pushed for the preservation of storm windows over single glazing in historic buildings, claiming that the argon or krypton gas all leaks out of double glazed windows, reducing their effectiveness; instead, that gas losses are negligible and "the functional service life of triple glazing is estimated to be above 40 years."

The windows were mounted in the building's insulation layer, at the building face, and being triple-glazed, were always going to be warm on the inside, so there is not going to be any condensation to rot them out.

Better insulation raises the interior surface temperature of window frames; thermal and humidity loads on the component are reduced. Moisture measurements in the pilot project after 25 years confirm this expectation; all substance is unchanged and dry throughout, so it can be expected to last at least another 25 years.

The only complicated piece of equipment in a passivhaus is the heat recover ventilator, and even this was in good shape. And thanks to the filters, even the ducts were clean.

There is a lot to learn from this. When you take a simple, "boxy but beautiful" design, a carefully detailed building envelope, and quality construction, then Passivhaus can keep delivering energy savings for decades.

With the investigation of this prototype building, combining both typical masonry and lightweight structures, after a 25-year period of normal use, it has been confirmed that the solutions based on the passive house concept offer a path to sustainable construction with a good life cycle balance: The energy consumption is negligible, stable over time, and, in addition, the durability of the components and the building is prolonged, including excellent indoor air quality and comfort.

And as Justin Bere notes and the study concludes, this makes a difference in justifying the embodied energy.

Therefore, the passive house concept assures significantly lower life-cycle costs. In addition, it is easy to have full renewable energy coverage in such a passive house leading to a really robust, risk-reducing, cost-effective and sustainable solution.

It also is a great justification for changing codes to make Passivhaus the minimum standard for construction; it has been proven to work over the long term, it is durable and dependable, and it locks in the savings in energy and carbon now and pretty much forever.

If we are serious about climate and carbon, then we should just do it.

In praise of the dumb home: A Passivhaus 25 years later
There is not much that can go wrong in such a simple concept. That's really smart.

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