Not Passive about Passive

Some things take time. My first book, Building the Timber Frame House, was written over 30 years ago. It was a personal manifesto about a better approach to building homes. I was convinced that conventional systems were inherently flawed and that we therefore needed a building system in which higher standards of durability and energy-efficiency were natural outcomes rather than occasional outliers. I made the argument that the dominant building methods invite shortcuts and poor workmanship, while also making energy-efficiency difficult to achieve because structure and insulation fight each other in the same territory.

I promoted timberframing as a solution for two reasons. First, timberframes are robust and visible structures that demand disciplined craft standards and result in buildings that can last for many centuries. Second, by applying insulation as an exterior covering layer,there is less need to compromise the insulation with structure, which I argued was an opportunity to maximize the building’s thermal performance.

Even so many years ago, I could see that our ability to make homes extremely tight and well insulated would lead to interesting challenges and compelling opportunities. I could also see a very exciting future, a veritable paradigm shift in our expectations of our buildings, and knew that the vision I was describing about building performance was even more important than the timberframe strategy that was the book’s subject. It was no accident that these were the last two paragraphs of that book: (Italics added)

To insulate as well as we can and to make houses as tight aswe can presents new challenges to the building industry. Houses will no longer naturally ventilate, because of our inability to get them tight.We can lock them up like thermos bottles if we like. To bring new air into the house, we’ll have to design ventilation systems into the plans.With heat loss cut to the bones, we’ll have design natural and mechanical recirculation to keep the temperature even and the air fresh.In this kind of environment, the heat from appliances, lights, and even body heat will contribute significant proportions to the small heating requirements. In houses built this way, energy from the sun, wind, or water could easily replace fuel-fired power sources.

Energy conservation is the hope of the future. In conscience, we must mark the end of the era of substandard housing that is cheap to build but expensive and wasteful to maintain. In conscience, we should begin a time when houses contain energy-autonomous environments that consume no fossil fuels and are built to last centuries.

Without giving that mission a name, I was describing what we now call Passive House or Net-Zero homes. I knew then that these types of homes were possible, and I knew that such a possibility therefore had to be realized, for it wasn’t just an idealized way of the future, but rather–even as I wrote those words in the late 1970’s–it felt like it was our future’s hope.

While our progress has not always been constant, I’m proud to say the mission of building durable, energy-independent homes has always been important. Real important.

We have just assembled our first Passive House. A time lapse of the 5 day shell installation is here. The home is still under construction, but we’re confident we’ll have achieved the stringent Passive House standards* when it is complete, which is basically the realization of the two last paragraphs in my first book. Energy conservation through extraordinary insulation and air tightness is the key to eliminating fossil fuels, and a sophisticated ventilation system is the solution for heat recovery and fresh air.

In a way, the Passive House requirement was not daunting because, at Bensonwood, we’ve been preparing for it with our continual performance improvements over the last 35 years. We’ve been inching ever closer to the “energy autonomous environments” I envisioned. In the past few years, we’ve built several Net-Zero buildings, which while not quite as demanding in proven performance, have very similar requirements. The Passive House standards attempt to achieve energy independence without a conventional heating, ventilation and cooling (HVAC) system, while Net-Zero allows renewal energy sources to make up the difference and also tries seeks to address the total home energy, not just heating and cooling. But there is little doubt that a good way to achieve Net-Zero performance would be to start with a Passive House.

In another way, the Passive House was a big and important step for us. It forced us to improve our air tightness to a level a little better than we had previously achieved. On previous projects, we had achieved .75 ach at 50 pascals, but Passive House requires .60. This is called “raising the bar,” a phrase that is often used, but not always appreciated for its potential significance.

Since I was a pole-vaulter in my high school years, the term “raising the bar” means something pretty specific to me. What I learned back then was that every new height, once leaped, made the height below it seem quantums easier. There was a time when I was stuck at 13’6″ for quite awhile, but a particular competition forced me to jump 13’9″. From then on, 13’6″ was a cinch. The same thing happened at 14′. I spent nearly a year hovering around that height, never doing better, until I somehow got over 14’6″ in a tough competition. From then on, 14′ was no big deal. (If you have no context, these were middling heights. I seldom won.)

So for us, building the Passive House is a lot like my 14’6″ jump. It couldn’t have happened without years of developing skills, training and continual improvement. But since we have now made the performance leap from .75ach to .6ach, we think .6 will be become relatively normal and .75 will be easy. In fact, we already think .6 will soon become our standard air tightness expectation and we look forward to setting our sights on an even better performance stand of .5ach at 50pascals.

The cool thing about the air tightness improvement is that it’s essentially free, where improving the R-value means increasing shell thickness and/or buying better windows, and that costs more money. Air-tight building is about attention to detail, discipline, and doing things correctly and precisely. It’s not about buying more materials; just installing the same ones a little bit better. Once the process is understood, it becomes repeatable with no penalty on production efficiency.

We recently raised our standard insulation level to R-35 (wall) and R-42 (roof). At this level, both Passive House and Net-Zero are within reach for most of our standard homes. With our newly-gained Passive House level of air tightness, we’re closer than ever to my 30+ year old vision. Being this close makes me anxious for the bar to be a bit higher, because I think we’re ready to make that leap to “begin a time when (all our) houses contain energy-autonomous environments that consume no fossil fuels and are built to last centuries.”

* Passive House standard from Wikipedia:
The building must be designed to have an annual heating demand as calculated with the Passivhaus Planning Package of not more than 15 kWh/m² per year (4746 btu/ft² per year) in heating and 15 kWh/m² per year cooling energy OR to be designed with a peak heat load of 10W/m²

Total primary energy (source energy for electricity and etc.) consumption (primary energy for heating, hot water and electricity) mustnot be more than 120 kWh/m² per year (3.79 × 104 btu/ft² per year)

The building must not leak more air than 0.6 times the house volume per hour (n50 ≤ 0.6 / hour) at 50 Pa (N/m²) as tested by a blower door.

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