It’s been almost a year since we started work on the Passive House in the Woods. It’s about time that it makes an appearance on the blog. So without further ado, here is an image and a description.

Passive House in the Woods rendering

The Passive House in the Woods is a 1,900 square foot two-story single family home with walk-out basement level, and a rooftop terrace. It sits on just over one acre in the Town of Hudson, WI—minutes from interstate 94. Located on the outer edge of a residential development, the home overlooks the St. Croix river valley. The building lot provides stunning views and prime passive solar exposure. The property’s north boundary is heavily wooded and borders undeveloped land. The design of the house works with the natural landscape, and minimizes impact on the wooded character of the lot.

Passive House certification mark

High Performance Building Envelope

Exterior walls, windows, doors, slab, and roof designed according to Passive House principles can radically reduce the amount of energy used to condition a building. The exterior wall assembly of the Passive House in the Woods consists of 11” Insulated Concrete Forms (ICF) for structure, and an 11” Exterior Insulation and Finish System (EIFS) facade with an overall R-value of 70. Windows and doors are Passive House certified, come with triple pane low-E coated glazings and insulated frames for installed R-values of 8. The slab sits on 12” of extruded polystyrene insulation with an R-value of 60. The flat roof utilizes an average of 14” of polyisocyanurate insulation with an R-value of 95.

High-Efficiency Mechanical System

The mechanical system in a Passive House is typically centered around a heat-recovery ventilation machine. In milder climates, this system provides all the necessary heating energy, as well as outside air needed for balanced hygienic ventilation. The heat-recovery ventilation system in the Passive House in the Woods consists of a high efficiency heat-recovery ventilator, combined with a 600 foot PEX-tubing loop field—buried on the property—to pre-heat and pre-cool the incoming air stream. This also dehumidifies moist summer air.

In extremely cold climates, the paradigm of heating with ventilation air changes slightly. The overall annual energy goals for Passive House can be met but the extreme cold winter temperatures require a small additional heat source. Electric in-floor heating mats with local room-air thermostats are used in the Passive House in the Woods to provide about 3kW or about 10.5kBtu*. That compares to the energy draw of two hair-dryers.

Renewable Energy Systems, Net Energy Positive Energy Balance, and Carbon Neutral Operation

Renewable energy systems are optional and not required by the Passive House standard. Our client chose to achieve a net energy positive energy balance and carbon neutral operation. A 4.5kW photovoltaic system generates a surplus of 65% over the energy consumed on site, avoiding 2.9 tons of CO2 annually*, and therefore providing carbon neutral operation for a household of two people*.

The domestic hot water system utilizes a 40 square foot hot water solar collector on the roof to pre-warm water in a 50 gallon storage tank. It is capable of providing over 90% of the hot water used in the home*. Backup heating is provided by a small electric on-demand water heater.

Minnesota GreenStar pending certification

Minnesota Green Star Certification

The Passive House in the Woods is registered with Minnesota Green Star and designed to achieve a gold rating.

The Team

The Passive House in the Woods is a team effort. We intend to post more on the design and build team members on a dedicated website in the near future. For now, we’d like to credit our building partner, Morr Construction.

Morr Construction logo

The Scoop

Currently, there are only about a dozen certified Passive House(TM) buildings in the U.S. The Passive House in the Woods is slated to become the first certified Passive House(TM) in Wisconsin, and one of only a few net energy positive and carbon-neutral buildings in the country.

It blends economy, ecology, health and durability in ways only Passive House can. The project sets out to demonstrate that this level of performance and quality can be achieved with today’s technology—even in an extremely cold climate. The Passive House in the Woods is a unique show-case. Construction is scheduled to begin in December 2009.

The Passive House Standard is the most rigorous building energy standard in the world. Consultants, projects or building components that have obtained the right to carry the logo have committed themselves to design excellence and the Passive House energy performance criteria.

*Performance figures are based on Passive House Planning Package 2007 calculations.

7 Comments

  • Dave Brach says:

    Looks like a really amazing building, Tim. I can’t wait to hear and see more. Congratulations and good luck with construction!

  • mike says:

    to continue the topic of embodied energy, polyiso has an EE of 110 MJ/kg while XPS has an EE of 70 MJ/kg. how do you come to grips with a carbon-neutral project that has such a high level of embodied energy? yes, the long term savings of the insulation more than make up for the deficit – but there are ways that this can be achieved using materials with significantly lower EE. it’s probably my largest concern about passivhaus.

    • Tim Eian says:

      Mike,
      Building high-performance building envelopes in an extremely cold climate is a real balancing act. I agree with your assessment of embodied energy and the importance of a complete carbon offset. In this context, carbon-neutral operation is a low-hanging fruit (sorry Architecture 2030 Challenge).

      Besides cost-factors, quality control, and build-ability, we found it to be most difficult to meet a low embodied energy goal with materials and assemblies that perform well in hygrothermal analysis. Making an assembly that is both robust, and benign is something we all strive for. First and foremost however, we need to deliver a durable product for our client. We hope to engineer assemblies around cellulose and other low-embodied energy insulation products—that’s actually where we started with this design. However, given the circumstance of cost, availability, building physics, and probably a million other things we looked at over this past year, we ended up with mostly EPS, some polyisocyanurate and some XPS. The BioHaus in Bemidji did a study on embodied energy versus operational energy (and operational energy savings). These things are not trivial. Not many clients would pay for services to take it to that level either. So once again, there is an ideal—and then there is the reality of having to provide professional services in the market place.

      BTW, I am not sure that this is a general issue with Passive House. In our case, it is much more climate driven. There is plenty of precedent for Passive House buildings that use entirely renewable, and low embodied energy materials. Those are usually located in more moderate climates, however.

      Thanks for sharing your insight.

  • Interesting project. We are in the planning stages of a new home that we intend to meet Passivehaus standards here in eastern Maine. Therefore all cold climate projects are of particular interest.

    I was curious what your position might be about use of very high R-value thin insulation products, like vacuum insulated panels in a project such as the one that you have working now?

    • Tim Eian says:

      Hello Roger,
      Thanks for your interest. We’ve looked at vacuum insulated panels briefly, as they were used for the BioHaus in Bemidji. The R-value is phenomenal but the detailing is rather tricky. For the first effort, we decided to be more conservative and stick with more common details. The basic structure is a standard ICF module, with a thicker than average EIFS facade. Therefore, many of the things builders already now apply. Again, we were hoping to stick with familiar paradigms. There are a couple of details where we are using vacuum insulated panels in order to maintain R-value, i.e. at the exterior shading elements, which are built-into the wall, and at the exterior door sills.

  • Hi Tim: Thanks for your quick response. I have had numerous conversations with three different manufacturers of vips and all are working on improved outer skins that would make them easier and more widely utilized in the building construction industry, both commercial and residential.

    We are particularly interested in vips because we are designing this house from an interior conditioned space standpoint. In order to meet our specific needs we intend to manage the exterior dimensions to not more than a certain footprint. Thus the overall size is important and the less sheer width of the wall will yield a reduction in overall footprint while maintaining th interior size that we want. VIPs will accomplish this provided the exterior skins can withstand reasonable care on the job site, and the fastening systems used can be improved sufficiently to allow a reasonable time factor for installation. I find it interesting that you are using these in some fashion in your project. Were your VIPs sourced from a European manufacturer?

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