Passive House

One of the many things that I have been up to is assisting with 'Weatherization Barnraisings' in my home town (more on this soon). Early on I sat in on a workshop on 'Air Sealing' (which basically means cutting down on places where the warm air in your house can leak out and the cold winter air come in). At some point the presenter started talking about 'Passive House' (or 'passivhaus'--this was developed in Germany) standards. He lost me entirely. It might have been because I was tired that night and on the edge of being sick, but I had no idea what he was talking about.

A few months later, I heard about a place in Jamaica Plain (actually Roslindale) in Boston that was working on being as ecologically correct as possible. When I heard that they were looking for volunteers to help, I signed up. I figured that I could do something that might be useful and, hopefully, I would learn something, too.

This was the JPGreenhouse, the future home of Andrée Zaleska and Ken Ward, two climate change activists, and their children. And the first thing that happened my first volunteer day was a tour of the place, conducted by Declan Keefe, the project manager from Placetailor, who are the folks that are doing the construction work. JPGreenhouse, as it turns out, is going for Passive House certification and Declan explained what that meant in a way that made sense to me. In fact, at this point, I have taken the tour three times, each time learning a bit more about how all this Passive House stuff works.

First and foremost, Passive House is a set of standards. For those who like the technical aspects of this stuff, Passive House US lists the standards for houses built in the USA:

Performance Characteristics:

• Airtight building shell = 0.6 ACH @ 50 pascal pressure, measured by blower-door test.

• Annual heat requirement = 15 kWh/m2/year (4.75 kBtu/sf/yr)

• Primary Energy = 120 kWh/m2/year (38.1 kBtu/sf/yr)


What does this mean? It means that any building that wants Passive House certification needs to meet three criteria: it has to be air tight (to the required measurements), it can't use more than a certain amount to heat it each year, and it can't use more than a certain amount of overall energy each year. Those exacting standards mean that very little energy is used in heating the building--and, in fact, very little energy is needed to keep the building warm year 'round. The joke is that you could practically heat the building by the body heat of the occupants. (Particularly if they were exercising or dancing or had a very crowded party.)

How does it accomplish this? Here are what one person (from the 100K House Blog) saw as the key elements of a Passive House. (I am changing this slightly so it's easier to explain.)

First, the House uses Super Insulation (that is insulation that is well above what used to be accepted as 'normal insulation'). Generally, new houses have more insulation, but Passive House buildings use a very high amount.

The insulation must be airtight (as I explained above) and must minimize what's called 'thermal bridging'. Thermal bridges occur when building materials conduct heat--thus allowing the heat to escape right through the materials (as opposed to through air exchange). In other words, because there are neither air exchanges nor points where heat is conducted out of the building, the warmth stays in the house. (That's assuming you want the house to be warm--if it's hot out and you want the house to be cool, it works the same way, except the heat stays outside.)

Second, the House has highly efficient windows. Windows are one of the easiest places to lose heat in a house. Most Passive House designs use triple paned windows with an inert gas in between to really minimize heat leakage.

Third, using a special ventilation system is very important. Because Passive House buildings are so airtight, stale air, germs, smoke, and toxic gases will stay in the building (creating the famous 'sick building syndrome' ) unless a special system is set up. These Houses use what's called 'Mechanical Ventilation with Heat Recovery'. The building's air is sent out of the building and fresh air brought in by means of fans, blowers, etc. Of course, this would defeat the purpose of keeping the building air tight if the warm air was sent out and cold air brought in (which is what would happen if you opened a window on a cold day). Passive Houses rely on Heat Exchangers (aka Heat Recovery Ventilators or Energy Recover Ventilators) which take the heat out of the air leaving the building and transfer it to the air coming in. (Of course these ventilators and exchangers have to be very energy efficient since the Passive House standards include total energy used as well as energy used in heating the house.)

Finally, since the House loses so little heat, what heat it does require can be gotten using simple, innovative, and efficient methods. The 100K House Blog lists four common methods that they've seen to heat the House: using a small heat pump, using a small condensing gas burner, using a small combustion unit for biomass fuel, or having one compact unit for all in one heating, ventilation and domestic hot water. (Or you could have a dance party every night!)

All this sounds very sustainable to me, since these houses use so little day to day energy. But the JPGreenhouse goes further. Andrée and Ken and the Placetailor folks were also concerned about the energy used in creating the building materials (also known as 'Embodied Energy'--the subject of my next post). So rather than using Polyisocyanurate (a foam material made--as most plastics are--from oil), they are mainly using cellulose (made from shredded newspapers) for insulation. Of course, to achieve the Super Insulation that Passive House requires, their walls have to be a lot thicker than if they used Polyisocyanurate. (And, actually, they are using Polyisocyanurate in a few places because it really made sense.)

In addition, the JPGreenhouse isn't a new house. Andrée and Ken bought an old store and are retrofitting it to Passive House standards. That means the builders have really increased the thickness of the walls. (It occurs to me that one way to make an old building a Passive House would be to build new outside walls over the old walls--creating a building within a building.)

What about costs? Declan pointed out that Passive House construction is only slightly more expensive than regular work, but it doesn't seem that way at first. As you put in all this insulation and expensive windows and exotic ventilation systems, the costs go up and up, well above average construction. Then, when it's time to put in the heating system, the furnace and ducts and everything that is used in an ordinary house, you don't need to. You've got a small heating system that not only uses little energy, but costs very little to install. And suddenly the costs slide back down toward where the average construction costs are. So for just a bit more, you've got a house that will use very little energy. I'm sure the payback period isn't very long.

A few months ago, I stumbled on an article in the Boston Globe that described a house that sounded a lot like the JPGreenhouse. But this place was in Roxbury, a completely different part of Boston. It turns out that this is the home of Simon Hare, one of the people behind Placetailor. He is also retrofitting an old house. And while it sounds like he is going to be as rigorous as Passive House standards (he wants something that won't need any conventional heat source at all), he is not going for Passive House certification. When I asked one of the Placetailor folks about that (I actually haven't seen Simon at the JPGreenhouse), the person told me Simon Hare didn't want to be constrained by the actual Passive House standards. In other words, he would be using the ideas without worrying about certification. (The JPGreenhouse folks are trying to be a demonstration, but Simon Hare is just working on his own house.)

So here is another set of ideas to think about as we build a sustainable society. We don't have to accept it all, but we can learn from it. Passive House isn't the final answer, but I think it raises a lot of useful points to think about.


Quote of the Day: "When Ken and I set out to create a new home for ourselves... we wanted to create a sustainable living space using very little energy and supplying much of our own food. We were astonished to find that there are few 'green' houses open to the public, and none in New England. Most demonstrations are also expensive new construction, not much help in rehabbing an old building on a moderate income. ... we purchased an abandoned 100 year old former neighborhood store ... to create the JP Green House - our home and an accessible model of zero carbon, sustainable living." - Andrée Zaleska