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Wolfe Island Passive: The Envelope

The two-bedroom home makes natural light a key part of the design

Posted on Oct 6 2016 by David Murakami Wood

Editor's note: David and Kayo Murakami Wood are building what they hope will be Ontario's first certified Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. on Wolfe Island, the largest of the Thousand Islands on the St. Lawrence River. They are documenting their work at their blog, Wolfe Island Passive House. For a list of earlier posts in this series, see the sidebar below.

After a couple of weeks of intensive work between the architect (Mikaela Hughes), our passive house consultant and middleman to the suppliers (Malcolm Isaacs), and ourselves, we have the final plans. With the house being factory-built from cross-laminated timber (CLT), there are far fewer changes we can make after this point than to a conventional stick-framed house. But we’re happy with things.

The house is small by North American standards, with under 1,600 square feet (or less than 150 square meters) of interior area, and that’s the way we like it. We’ve tried to combine elements of what people around here expect a house to look like, to reflect something of the village feeling, but at the same time, this is not an ordinary house nor does it entirely look like one.

However, the differences are subtle — at least from the outside.

Passive solar orientation

First, the orientation and balance are not what people would expect. The windows are predominantly on the south side, regardless of the view, in order to maximize passive solar gain. The southern roof will be completely covered in panels for solar water heating and PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow. generation. The windows on the east and west bring in light in the morning and evening but also are designed for cross-ventilation in the summer. On the north side, windows are minimal, but this also produces an interesting and slightly whimsical pattern.

This solar orientation also affects the interior structure and layout. Places where we will spend most of our time and want to be brightly lit and warmest all are on the south side, whereas the north side of the house has all the utility spaces.

Downstairs, an open floor plan

The ground floor is dominated by a relatively large space, running the whole length of the house, from the kitchen in the east through the dining room to the lounge in the west. I use the conventional terms because that’s how we’re thinking of the space, although the latter two "rooms" are entirely flexible in how they could be used and laid out.

The main entrance is in the northwest corner, and this is where the first element of Japanese thinking comes in. The "genkan" (entrance hall) is a place where you take off outdoor clothes, including shoes — we don’t wear outdoor shoes in the house — and there is a deliberate change of flooring to indicate where this transition occurs. Also in the north half of the ground floor is the utility/machine room, where all the tanks, the energy-recovery ventilator(ERV). The part of a balanced ventilation system that captures water vapor and heat from one airstream to condition another. In cold climates, water vapor captured from the outgoing airstream by ERVs can humidify incoming air. In hot-humid climates, ERVs can help maintain (but not reduce) the interior relative humidity as outside air is conditioned by the ERV., the control panels, the washing machine, etc. will be. And finally, there's a dedicated pantry for all the kitchen and food stuff, freeing up the kitchen area itself for actual cooking (which we both enjoy).

The bedrooms face south

Upstairs, there is a small landing area, and again the south-north split is evident. On the south side, we have two generously sized bedrooms, and in between a Japanese sitting room with a raised wooden platform covered with tatami (woven grass) mats. This will also double as a guest bedroom, with futons stored beneath the tatami. To the north, there is a walk-in closet, which could be converted into a smaller bedroom if necessary, and on the northeast corner, a Japanese-style bathroom space, with separate water closet, a changing room, and a wet room containing the shower and soaking tub.

The chimney from the stove, the solar thermal pipes, and the PV cables will run through the central core of the house from the utility space below up through the storage attic above. The whole house is designed to minimize the distance that water has to travel and the length of pipes from toilets, etc.

Outside, the roof extends well out from the wall line, to provide shade for the upper windows from the harshest overhead sun, while maximizing the solar gain at other times. Downstairs, the same effect is created by the porch that runs all along the west and south sides of the house.

Twelve inches of rigid foam under the slab

The most important thing about a Passive House is the envelope: the foundation, walls, and roof. In the sections drawings (see Image #4, below), you can see what we are going for.

We’re not deviating much from the standard way most Passive Houses do things with the foundation, which will be an engineered concrete slab with 12 inches (305 mm) of expanded polystyrene (EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest.) insulation beneath the slab and about 10 inches (255 mm) of vertical EPS at the edges. The insulation continues out well beyond the foundation itself to provide a frost skirt around the whole foundation. This is the only significant amount of petroleum product we’ll be using in the whole house and one that couldn’t be avoided.

The timber walls are over 4 inches thick, not counting insulation

The external walls of the house are 4 1/3 inches (110 mm) thick cross-laminated timber (CLT), wrapped in 11 inches (280 mm) of rigid wood fiberboard insulation, followed by a vapor-permeable moisture barrier and local white cedar siding. The CLT sits on the concrete foundation and the fiberboard forms a continuous layer of insulation with the EPS beneath.

The roof also is CLT, but there’s a lot more fiberboard insulation up there: around 14 1/16 inches (360 mm). The roofing will be steel. This will last a long time, and when it does eventually need to be replaced, it can be recycled.

R-50 walls and an R-60 roof

So how will this design perform? What about R-values and U-factors?

The wall structure should be just over R-50, and the foundation significantly better. The roof structure will be more than R-60. There will be other houses with higher claimed R-values, but the figures here are not claims but are based on tested values for the components, certified by the Passivhaus Institut in Darmstadt, Germany.

What’s more, with the precision cutting of the manufacturing — we’re talking 1 mm tolerances — the tightness of the house will be unparalleled, and the windows and doors (about which more in a later post) will be much better performing than any equivalents more commonly available in Canada.

There are other considerations when it comes to what kind of R-values we are aiming for. First, we’re by no means in the coldest part of Canada: -25° Celsius (-13°F) is about as cold as it gets here in February — and it is never that cold for more than a few days at a time — compared to -45°C (-49°F) in places like Edmonton.

Second, we will have to burn some wood for water heating anyway, which means that the house will never be anything less than comfortably warm in winter. And finally, we already will be exceeding the requirements of the Passive House standard. In short, pushing for much higher performance would mean significantly increased costs and a more bulky look to the house, and all for very limited noticeable gain.

We think we’ve got the balance right.

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Image Credits:

  1. David Murakami Wood

Oct 6, 2016 11:25 AM ET

Old school CLT
by ven sonata

It suddenly occurred to me that panabode is kind of the original CLT. They are solid cedar 4"x6" with tongue and groove that were invented in the 50's. Without insulation they are inadequate, but with exterior fiberboard they would function in much the same way as CLT. The interior walls are left as finished cedar. There are many kits of all shapes and sizes for shipping and would be no doubt easier to ship than full scale walls. Any thoughts?

Oct 6, 2016 9:10 PM ET

by Malcolm Taylor

I've built about a dozen Panabodes over the last twenty years. The big difference between them and CLT is the initial shrinkage and seasonal movement. Like log structures that movement has to be built into all the windows, doors, stairs and post details. I'm not sure how exterior insulation would work.

Panabode has had ongoing problems with code compliance, both because of inadequate insulation levels and seismic concerns. Some time ago they went from a 2 1/2" wide 'log" to 3 1/2" in an attempt to deal with these issues. As you can imagine that also increased the price substantially. I don't know where they are with all these issues right now.

Oct 7, 2016 1:15 PM ET

Japanese elements

I love to see the O-furo in the bath. I miss going to the Sento. And yes, I am also putting a Genkan into the Net-Zero-Ready house I am building in "Glosta" Mass. Japanese style, no shoes in the house. With Shoji. Not paper though for little grandchildren fingers to poke through- Kalwall (acrylic) panels framed in wood. But no Tatami. (Where would you get Tatami in the US or Canada?) Still figuring out where to put the Tokonoma. Japanese-American "Fusion" house?

Oct 7, 2016 1:23 PM ET

James Kreyling ...about Tatami
by ven sonata

The surface mat of tatami can be ordered on line for about $25 mat. These days we simply attach the mat to closed cell foam mat and it is immune from the damp. It is also more comfortable like that. Traditional units cost $180 and weigh about 50 pounds and should not be used on damp surface.

Oct 12, 2016 3:07 PM ET

Edited Oct 12, 2016 3:08 PM ET.

by Michael McCann

Great layout IMHO. I love the large, bright, open Kitchen, dining, living areas. I love the large pantry. I love the large walk-in closet upstairs that COULD be made into a bedroom.

And, my intuition says that the south-facing windows are large enough that the house is likely to overheat in the winter. Please keep us posted on performance during the winter of 2016-2017.

Oct 21, 2016 10:43 AM ET

Edited Oct 21, 2016 11:48 AM ET.

overheating (and more)
by David Murakami Wood

Dear all,

Thank-you for the comments. I'm sorry we haven't responded earlier but I was having trouble with my GBA account - seems to be fixed now.

On the question of overheating via the large south-facing windows, both the main roof overhang and porch are specifically designed to prevent 'high sun' from heating the building in summer and shoulder seasons. It's very important with houses that use passive solar design to take account of the angle of sunlight at the specific latitude at various times of year. Jumping ahead (in terms of this guest blog), we noticed the difference immediately that the porch was built in cutting the excess summer sun heating through the downstairs windows. We are yet to see how it will be in winter, but it seems to be comfortably warm in the fall without even deploying the HRV. In general, excess heat is a happier problem to have to deal with in the Canadian winter than not enough!

On the Japanese room, we'll be writing about that soon (on our own blog). Our tatami mats are real tatami, not the foam pads with matting on top. If humidity is a real problem for you then the latter are okay, but they are nothing like the real thing! Although we haven't had the monitoring equipment installed yet to measure (and we may have it from this November), passive houses tend to be drier than normal houses, if anything, so we don't have the problem of damp to contend with.

On the Japanese bathroom, this is now compete IRL and it is beautful. Just waiting for the glass doors to be installed and the electrical supply for the hot water to be connected and we will be able to use it. Again, there will be a blog entry soon...

Thanks again of the comments, and please feel free to ask any questions in these threads or directly!

Dec 21, 2016 6:10 PM ET

CLT Supply
by Ethan T ; Climate Zone 5A ; ~6000HDD

I've been in contact with various CLT suppliers, including Zublin. Zublin put me in touch with an outfit in Bozeman, Montana as their US contact. Did you work through a North American contact for your CLT or direectly with Zublin. Thanks!

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