passive [pasiv] house [haus]
by Rob Harrison
The term passive house (Passivhaus in German) refers to the rigorous, voluntary, standard for energy efficiency in a building, reducing its ecological footprint.
It results in ultra-low energy buildings that require little energy for space heating or cooling. Although it is mostly applied to new buildings, it has also been used for refurbishments.
The standard is not confined to residential properties; several office buildings, schools, kindergartens and a supermarket have also been constructed to the standard.
Passive design is not an attachment or supplement to architectural design, but a design process that is integrated with architectural design.
Passive House projects use a lot less energy than conventional buildings. By virtue of their advanced super-insulated design, there are no drafts in a Passive House. Energy modeling tells us how to keep the heat out, so they’re cool in summer. Indoor air quality is demonstrably better than in standard construction, with more HEPA-filtered fresh air. (Good for smoke season!) Passivhaus houses are amazingly quiet. Big high-performance windows let in plenty of natural daylight. Tuning the design to the exact site and climate minimizes energy used for heating and cooling, so mechanical systems are small and simple.
Here are some key elements in a Passive House:
- The house as designed meets Passive Haus standard with a specific space heat demand of 42 Kbtu/SF/year
- R-48 exterior walls, slab on grade and floor over unheated space
- R-79 roof
- Mini-split heat pump provides supplementary heat
- Heat pump water heater
- CFL & LED lighting
- EnergyStar appliances
- No petrochemical fuels
- Utility inter-tie photovoltaic system (capacity as yet unspecified) may generate enough electricity to achieve net-zero energy
- Tulikivi masonry stove will burn wood efficiently
- Full line job-site recycling
- Advanced framing reduces wood use by 25-30%
- Full modules for panel siding
- 35% fly ash in concrete
- Blown-in cellulose (recycled newsprint) insulation in walls and roof
- Fiber-cement siding and trim
- Engineered lumber for roof and floor framing
- Dual-flush toilets
- Downspouts routed to future pond for irrigation
- Natural ventilation through stack effect
- Additional mechanical ventilation will maintain excellent indoor air quality
- Low toxic paints, caulking, concrete finish, formaldehyde-free casework used
Examples of Passive House in our Area designed by Harrison Architects
Laurelhurst Backyard Cottage
This project is a near-Passivhaus backyard cottage in the Laurelhurst neighborhood for a prominent civic leader. We started the design process with a larger, 800 SF two-bedroom two-story cottage in mind. As my client’s thinking about the cottage evolved, the design became smaller and smaller. We ended up with a 330 SF cottage with mezzanine bedroom overlooking the main floor. The design of cottage compliments the adjacent house, but does not imitate it. It fits purposefully on the site, tucking in where it will have the least impact on sunlight in the house and yard, and the least visual presence. With its tiny footprint it fills the least portion of the back yard possible. The long sloped roof preserves views from inside the house and still allows western sunlight into the back yard.
The footprint of the cottage is minimal. I drew on childhood experience with house trailers. There is room for a sofa, dining table and chairs. There is a full size shower with a bench in the bath. The shower and bath will have windows out to a private garden screened with fencing and planting. The stair up to the bedroom is full size, so it will remain more easily accessible to an older adult. The stair is a form of tansu, a Japanese storage stair, with kitchen storage, laundry and utilities built in underneath. The bedroom has full standing headroom, with the roof draped over it like a tent. The bedroom is designed to be flexibly used, as either a place to sleep or home office, or both.
I try to only try one new thing per project. At the start of my greenbuilding practice here in Seattle 30 years ago it was tempting to incorporate as many of the new green technologies, materials and finishes as we possibly could. There were a few goofs. With the benefit of that experience we now have a full sophisticated palette of healthy and resource-efficient materials, finishes and technologies to achieve any goals our clients desire, backed by years of first-hand experience. On this project the one new thing is that I am trying “Glavel” for the first time. It is insulating glass gravel. It replaces both the rigid foam under the floor slab and the normal stone drainage gravel under that. Glavel has low embodied carbon, and using it replaces several steps in the construction process. Using Glavel under the slab will allow a fully foam-free project. (Exterior insulation will be mineral wool.) I will report back!
Okanogan Passivhaus Cabin
This 1,100 square foot near-Passivhaus cabin sits on a west-facing slope in high desert second-growth fir, Ponderosa pine and tamarack forest near Wauconda, WA. Construction was completed in 2012. The cabin is a year-round weekend and vacation retreat for the family, and may become a full-time home after retirement.
The cabin sits at an elevation of 4,250’ above sea level—the same as Stevens Pass. If you’ve been up at the Pass in winter, you know it can get cold! The heating system of this cabin is two electric in-floor radiant mats in the two bathrooms and another mat under the tile in the entry—that’s it! In the winter a tiny wood stove is fired up (with kindling basically) when they first arrive to bring the cabin up to temperature, and then the cabin remains comfortable for the duration of their stay. When combined with the occasional warmth of the sun, and the super-insulated walls, floor and roof, and high-quality windows, and the heat-recovery ventilation, the activities of several people cooking, showering, walking around, dancing and so on contribute enough heat to keep the house toasty.
In design, the insulation is tuned to be just the amount needed to allow the house to balance well. It depends on the very specific climate, trees, hills and buildings nearby. In the mountains, the insulation will be a lot. In the lowlands, more than usual, but not much more. A sophisticated energy model allows accurate prediction, so we can get it “just right.”
For more about this cabin, please have a look at our website: https://harrisonarchitects.com/portfolio_item/bonaparte-near-passivhaus-cabin/
About Rob Harrison @ Harrison Architects
I have more than forty-two years of experience as a design professional. I’ve been doing green design in Seattle for thirty years. In 2000 I co-created the Healthy House training. In 2009 I became one of the first 100 Certified Passive House Consultants in the United States. Our team uses advanced BIM software that allows easy virtual walkthroughs. Our Art and Design Maven finds reclaimed materials, sources original art by local artists, and brings it all together in a warm, beautiful setting. We speak hygge!
Please visit us at harrisonarchitects.com or drop us a line at email@example.com. We’d love to hear from you.