Take a Peek Inside the Walls of a Super-Home
How are today’s top energy-efficient homes built? We went in-depth with Passive House designer/builder Phil Dennis to give you a closer look.
Phil is nearing completion of this beautiful 5-bedroom, 2500 square foot home in Gaspereau, Nova Scotia, Canada. The house is designed following the Passive House standard. It is so well-insulated that the annual heating bill will be less than $180 per year in this cold winter climate. Yes, that’s per year. And the construction cost is under $200 per square foot, comparable with other custom-built homes in the area.
How did he do it? Here is the step-by-step process:
1. Choose a simple shape
The shape of a house affects its energy consumption. The shape of the house Phil designed is a cube with a roof on it – 32 feet wide x 32 feet long x 32 feet high – and for a reason. A cube is one of the most energy-efficient shapes for a cold climate because it has a low surface area, minimizing its heat loss for its relatively large interior volume. This is the same reason a two-story home is more energy efficient in a winter climate than a one-story home of the same interior volume.
Without a lot of cut-outs or complex angles, simple shapes are also easier to insulate and air seal. If you choose the simplest house shape that works for you, your construction costs are lower, and your sustainability goals are easier to reach.
2. Insulate the foundation and slab thoroughly
Contrary to the popular saying, heat doesn’t just rise. It goes out through every surface of the house, including the bottom. The new super-efficient homes have thick insulation around the foundation and slab, and this home is no exception. Under the slab is 8 inches of rigid expanded polystyrene insulation.
The basement walls are made of insulated concrete forms (ICF). Still, they’ve got an extra layer of 4-inch expanded polystyrene foam wrapped around the outside for a total effective insulation value of R-60.
3. Build Thick Walls
The walls of this house are 16 inches thick. It’s got two walls – a structural wall on the inside and a thick wrap of insulated, non-structural wall on the outside. The inside wall is 2 x 6 wood frame construction, insulated with mineral wool batts, quite normal for a house these days. But what happens after that is the amazing part. A second wall will be attached around the exterior.
The inside wall contains all the wiring and plumbing and is sheathed with oriented strand board (OSB) sealed airtight with tape to create an air and vapor barrier. In the photo below, you can see the air sealing tape. You can also see how thick the outside wall will be by looking at those wide window boxes. This is doubly amazing when you realize that a six-inch wall (a ‘standard’ wall) is already on the inside of this layer.
The outside layer is made of Larsen trusses, a lightweight wooden truss made to hold a thick layer of insulation – 10 inches thick in this case. The Larsen truss is an ingenious structure invented in 1979 by John Larsen, a renovation contractor in Edmonton, Alberta, Canada. It is now used for super-efficient homes in cold climates around the world. In the next photo, the Larsen trusses have been installed over the surface of the walls, surrounding all the window boxes.
The outer wall of Larsen trusses was filled with blown-in cellulose insulation, which is made from recycled newspapers and provides a thick, dense layer of insulation. The outer layer was sheathed in plywood, with 1/8 inch gaps between the plywood pieces to allow humidity to escape the wall. Then it was wrapped in house wrap to provide the wind barrier.
The effective insulation value of this wall is R-60. The exterior is finished with wood strapping and natural spruce tongue-and-groove boards stained a beautiful reddish-brown.
As the walls are completed on the inside, the wide windowsills show you this is no ordinary house. Look how thick these walls are!
4. Insulate The attic To The Max
Cellulose insulation is piled in the attic more than 2 feet thick for an insulation value of over R-100. The attic is easy to insulate when it’s an open truss space over the ceiling like this house. Phil was still able to get some of the look of sloped cathedral ceilings on the upper floor by using scissor trusses that slope up in the middle, with a raised heel at the eaves to leave plenty of space for insulation.
5. Seal All The Air Leaks
To make a house this energy efficient, you need to seal all the drafts and air leaks, so your heated air doesn’t escape. Fresh air is then provided by an efficient and clean heat recovery ventilator. To seal all the air leaks requires planning a continuous leak-free barrier and a lot of attention to detail. The photo below shows the air seal around the pipe that goes to the outside water tap, so you can see just how careful the builders were with sealing air leaks.
This kind of house aims to reach an air leakage value of 0.6 air changes per hour (ACH) or lower, at 50 Pascals (Pa) of air pressure difference. This house passed its air leak test with flying colors, at an astonishingly low 0.2 ACH.
6. Use High-Quality Windows
The windows are triple-glazed, argon-filled, with low-emissivity coatings and insulated frames and spacers. They seal well with casement closures rather than sliders, and many of them on the south side are fixed windows to prevent air leaks.
7. Have some fun with it!
You need to have fun sometimes! Phil shows his fun side by designing playful spaces into the house, including a play loft high up in the second floor that the kids can climb into on a ladder, a space in the library for a model train set to run around up near the ceiling, and a spot under the stairwell designed for the kids to hide in. Indoor playtime is going to be a blast in this house.
And not to forget some fun for the adults too. What is that extra blue pipe in the kitchen wall? It’s a beer line. Yes, you heard right. There will be a beer tap in the kitchen. ‘Nuff said.
The (nearly) finished house. The exterior doors haven’t arrived yet, but it’s still 4 months till winter sets in.
Article by:
Wayne Groszko
Wayne Groszko is a consultant, researcher, and teacher in Energy Sustainability with 13 years of experience. He has taught at Dalhousie University and the Nova Scotia Community College, in the Faculties of Engineering, Environmental Science, and Energy Sustainability Engineering Technology. Wayne is also President of the Community Energy Cooperative of New Brunswick, and has worked as Renewable Energy Coordinator with the Ecology Action Centre in Nova Scotia. He holds a B.Sc. (Hon.) from the University of Calgary, and a Ph.D. from Dalhousie University.