Mini-B is a tiny little thing.
It stands for “Mini-Bungalow.” It’s a prototype 300 square-foot “Detached Accessory Dwelling Unit.” In the Seattle area, you can plunk it down in your back yard for a guest house, or for grown-up kids who need to stay with Mom and Pop for a while.
Though small, it has a kitchenette, three-quarters bath (shower but no tub), living/dining room, bed loft, closet, equipment loft with storage, solar hot water collector, and vaulted ceiling.
It conforms to the International Residential Code and is considered a “modular” building in the State of Washington, says the building’s designer, Architect Joe Giampietro, Johnson Braund Design Group, Seattle.
Mini-B is built to an energy conservation standard that uses as little as 10 percent of the heating energy used by similar houses built with traditional methods and materials. It’s a conservation standard that can slash heating bills up to 90 percent.
When the last inspection and test is completed, Mini-B will be certified a “Passive House” by Passive House Institute US.
Passive houses are well-insulated, almost 100 percent air-tight, and they provide plenty of fresh filtered outdoor air at all times. They’re heated by passive solar gain, by heat from people and electrical devices. You can get additional heat if you need it, by more traditional means, but you’ll only need a little.
Because Passive Houses are well-insulated and extremely air-tight, a little heat goes a long way. Heat energy loss is small.
Power use is so low that with a small photovoltaic array to generate power, you could easily make the Passive House carbon neutral, Joe says.
There are a few Passive Houses in the U.S., and over 20,000 in Germany and Austria. The Passive House idea took root in Europe after originating in the United States. It began here in the mid-80s as a way to achieve energy efficiency via super-insulation, airtight construction, high-performance windows and heat-recovery ventilation Joe says.
Students in Seattle Central Community College’s Wood Construction Center are building Mini-B. It’s mostly complete as of October 2010, Joe says, with the students finishing up interior details.
The completed Mini-B will go on display for six months at Seattle’s Phinney Neighborhood Association center. After that, Joe says, it’ll go on the market, and more will be built for sale.
Mini-B’s air tightness – the building envelope’s ability to limit heating and cooling losses via air leaks – will help buyers recoup their investment through drastically reduced energy bills, says Joe.
Mini-B achieves much of its extreme level of air-tightness via PROSOCO’s fluid-applied R-GUARD FastFlash System. This air and waterproof barrier was originated by PROSOCO’s business partner BEI (Building Envelope Innovations), Clackamas, Ore.
Its four components address every possible way a building envelope could leak air. When heated air leaks out into winter cold, of course, it carries energy dollars with it. When hot summer air leaks into air conditioned spaces, it increases the load on the HVAC system.
In both cases, the warm air carries water vapor. If, on its way in or out, that warm air hits a chilly-enough surface, the water vapor it carries condenses. That provides moisture, an essential ingredient for mold, Joe explains.
By stopping the air leaks, the FastFlash system reduces the chances of mold developing in the walls. Since the FastFlash system is vapor-permeable or “breathable,” it can let small amounts of vapor exit the building envelope – in other words, if walls do get wet inside, they can dry out again.
Sealing the structural walls begins with filling all joints and seams – major air leak points — with R-GUARD Joint & Seam Filler. It goes on like caulk, but tools and spreads like a coating, with a knife, trowel or spatula.
The next step is sealing the structural framing of the rough openings for doors and windows with R-GUARD Fast Flash. Like Joint & Seam Filler, Fast flash is a sealant-like, yet spreadable waterproof detailing compound.
It was a good choice, said Frank Mestemacher, the instructor at Seattle Central Community College who supervised the students constructing Mini-B.
“I’ve used fabrics and adhesives to seal rough openings,” he said. “To seal them tight, you have to overlap the material. That gives you a buildup which makes it hard to fit the windows into the rough openings. Usually the material gets torn, which defeats the purpose of the barrier.
“The liquid flashing we used gets into all the cavities, knots and joints, and seals the rough opening up tight.” Frank said. “But you get nice neat corners that make it easy for the window frame to go in.”
When dry, the flashing is also durable and self-sealing, so the tears and scrapes associated with fabrics and adhesives don’t happen, Frank said.
Then, the entire wall assembly gets a roller-application of R-GUARD Cat-5 primary air and waterproof barrier. Cat-5 takes its name from the fact that, though breathable, it seals structural walls against air and water ingress in weather conditions from normal up to and exceeding a Category 5 hurricane – even before the cladding goes on.
The students rolled it on over the plywood panels as well as the filled seams between panels. Cat-5 ties the entire assembly together in one seamless, continuous coating, which is what you’ve got to have to stop air leaks through the envelope, Joe said.
Cat-5 also serves as a secondary drainage plane, in case water gets through the cladding.
All three components are instantly waterproof, so you can apply them to damp surfaces. That means no delays due to rain, usually a major advantage in the Pacific Northwest, though Joe said rain wasn’t much of a factor during construction of Mini-B.
The fact that these components bond tenaciously to structural walls wet or dry was also important, Frank said.
“I’ve seen paper wraps where the wind just tears them away from the building before the cladding goes up,” Frank said. “We liked these products because they adhere.”
Once the window and door assemblies were in place, the students used R-GUARD AirDam, interior sealant used with backer rod, to seal the space between frames and rough openings.
The weather-tight seal keeps expensively conditioned air from escaping through gaps between the frame and rough opening. It ensures water from outside is diverted to flashing, and outside air can’t leak in.
The fact that the FastFlash system doesn’t rely on layering like tapes and building papers do is huge, Joe says.
That air-tightness makes it possible for the HVAC system to efficiently do its job of frequently exchanging used inside air for fresh outside air.
That was verified in July when energy auditors conducted a calibrated blower-door test.
This test uses a powerful front door-mounted fan to pull air out of the house, and measure how much air gets pulled in through leaks in the building envelope. It verified Mini-B meets Passive House standards of .60 Air changes per hour at an air pressure of 50 Pascals.
That’s about one tenth of the air-changes in a typical house, Joe said. That’s because the fresh air in the house does not come through the wall, but through the full time ventilation system.
“A ‘house that breathes’ is another way to describe the Passive House,” Joe said. “It breathes vapor through the walls like our skin, and air through the ventilation system like our lungs.
As energy costs soar, Passive House and other energy-efficiency concepts are gaining greater traction, Joe says. He points to a recent “Passive House” article in the New York Times; Passive Houses in Vermont, Illinois and Washington; and increasing numbers of Seattle-area construction professionals who are adopting Passive House-type concepts.
“For me, one of this project’s biggest benefits has been learning to apply the principles of low-energy and high-performance,” Joe said. “Placing windows appropriately for solar gain; specifying high-performance windows; stopping air leaks through building envelopes; installing heat and energy recovery ventilators — these and other ideas can be used individually or together to improve performance and energy efficiency in any building.”
It’s a new approach, driven by ever-increasing fuel prices, he said. For homeowners, it holds the promise of taking fuel prices right out of the household budget equation – or at least putting them in a more affordable perspective.
That’s one big shining promise, embodied in one very compact house.
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