Construction Materials and Methods
In order to achieve the high level of thermal insulation, and the very low level of air infiltration, that a Passive House™ requires, we decided to build with on-site constructed “concrete-structural-insulated-panels” (C-SIPs). Esssentially, the house is built with thick EPS (“styrofoam”, “whiteboard”, “Expanded PolyStyrene”) walls and roof with thin layers of GFRC (“Glass-Fiber-Reinforced-Concrete”) adhering to all surfaces of the EPS. This makes a structurally strong “panel” for walls and roof that distributes the forces on it throughout the panel, using about half of inch of concrete as a coating. With sixteen-inch thick EPS, as we are using for the exterior walls, we achieve a R-value of about 60, or about 3 times as much insulation as the current (upgraded) Michigan Building Code requires for our region. Pre-construction energy modeling suggests that in the worst times of Michigan winters, to maintain a comfortable 70° F. indoors, this house will only need about as much heat as a hair dryer produces.
We should note that this is not a conventional way of building Passive Houses™. Most are built using some version of wood-frame construction (often with a truss between the inside and outside walls) that allows for a large amount of insulation in the exterior walls, and with much diligence in sealing all potential leaks in the air/moisture barrier layers. Several examples of these construction techniques exist in U.S. midwest Passive Houses™.
Also, note that though were are using EPS foam and concrete SIPs, this building method is not the same as ICF, or “Insulated Concrete Form” construction. ICFs have the EPS foam, typically two inches thick, on the outside of the concrete, creating the formwork for pouring the concrete, and providing insulation for the building. At the time of planning our building, we were not able to find ICFs in the USA that could provide an R-60 insulation value. We also thought the C-SIP method would be less expensive, uses less concrete, create a longer lasting building, and require less long-term maintenance.
However, evaluating GFRC-SIP construction method (as of February, 2013), I (Chris) do not recommend this construction method for building Passive Houses™. It is extremely labor intensive, and fairly wasteful of expensive concrete admixtures. This makes it a very expensive method of building structures. It may be better suited to a desert climate, where a builder does not need to be concerned with vapor/air barriers, but for our midwest climate, ensuring a good vapor barrier with the concrete layer increases labor time dramatically, particular when installing the plumbing, electrical, ventilation, and any items attached to the walls (cabinets, doors, etc) . As with wood-framed super-insulated structures, in climates where one needs to be concerned with maintaining a good vapor barrier, perhaps it would be most appropriate to separate almost completely the wall containing the insulation from walls containing the mechanicals. Also, if one separates the structural elements from the insulating elements, i.e, provide a structural framework for the building such as a timberframe, then the GFRC coating on the foam becomes a protective coating only, eliminating a thickness requirement, and some adhesion requirements, for the GFRC. Another problem with GFRC-SIPs in our climate is cracking of the GRFC due to differences in the thermal expansion rates of the EPS and the GFRC. On the plus side, GFRC is a very strong concrete, and combined with SIP technology, it produces a very strong structure – perhaps good for tornado or hurricane areas, and very good for small structures.
Built into side of hill – and insulated slab – info forthcoming.
Passive Solar Design – and daylighting – description forthcoming.
Windows – info to come.
Lowering Fossil Fuel Energy Consumption Further
This building is connected to the electric grid (at least initially), and is not using any other fossil-fuel based energy sources. Since grid-supplied electricity here in Michigan is mostly generated from burning coal, eventually we hope to shutoff grid-supplied electricity by implementing a combination of energy-efficient appliances and renewable-energy sources.
The appliances include an extremely efficient HRV – Heat Recovery Ventilator – to bring fresh air into the house. This unit captures much of the available heat (or coolness in the summer) from the exhaust air as it ventilates, and transfers that energy to the incoming fresh air. [If living in the house proves that it would be useful, we may transition the unit to an ERV – Energy Recovery Ventilator – to also capture some of the humidity in the air being exhausted during the winter .] The lighting is to be all LED, compact fluorescent, or fluorescent, for a 70 to 80 percent reduction in electricity consumption, and heat production, over conventional incandescent lighting. The kitchen appliances include an induction cooktop, a convection oven, and well-insulated efficient refrigerator, all of which will use less than 70 percent of the conventional appliances. Some appliances will use low-voltage DC, and some normal AC (eventually from the battery bank thru an inverter). The toilets are composting toilets, consuming no water. Low-flow fittings will be used on all sinks and showers to reduce the amount of water used, which also reduces the amount of energy needed for heating hot water and pumping water.
Heating energy, besides from passive solar energy entering through the windows, will come from solar hot water panels (evacuated-tube style), storing heat in a large hot-water storage tank. PV- PhotoVoltaic – solar panels will provide electricity which will be stored in batteries, and they also provide appropriate window shading, acting as adjustable awnings.