One year ago we traveled to Germany to visit the BAU ‘09, a huge international building trade show held every 2 years in Munich, Germany. We went to the BAU with the intention of learning more about European building products and their (in some cases) exceptional design and performance. At the BAU we found several products that we ended up importing and utilizing in the construction of the prototype. The most important of those were the windows and doors from EGE Fenstern und Turen.

The windows arrived from Germany in late November after being shipped across the Atlantic in a 20’ container. When they arrived on site, as per the shipping contract, we had 2 hours to unload the windows and doors from the container, and while 2 hours seems like a reasonable amount of time to do this, the size and weight of the windows (up to 500 lbs) made that somewhat complicated. Thanks to our focused crew, the windows were not only unloaded in the two hour limit, but also then installed in one day.

The most important attributes of the German windows we chose are the insulating and solar heat accepting properties of the glass and the operability and air tightness of the window frames.
The glass and Low-e coatings: standard windows in North America are double-glazed with low-e coating designed to reject most of the solar heat that hits them. In short, they are designed for cooling climates, where accepting solar gain usually means over-heating. In Maine, where we have a serious heating climate, standard glazing ends up rejecting 70% of the sun’s heat energy that hits the glass. Coupled with a very low R value (or insulation value) of about R-3, south-facing windows end up rejecting and losing more heat than they gain! The windows we imported from Germany are triple-glazed and accept about 50% of the sun’s heat that hits them. Coupled with an incredible R-value of about R-8.5, they basically become the home’s heating system, as they allow solar energy to pass through them and then hold the heat in the building.

The frames: the German windows are also built to be air-tight, with beautiful, solid, clear-finished pine frames and multi-point locking hardware, which create an air-tight seal between the sash and the frame when closed. The exterior of the windows have a painted aluminum cladding that creates a durable weather-tight seal to the glass, and requires little to no maintenance over the life of the window.

In order to verify the air tightness of the building shell and the windows, we conducted a preliminary blower door test. The result of the test showed that with the windows installed and sealed, the building’s shell is amazingly air-tight, surpassing the Passive House requirement of .6ACH. This incredible performance is attributed to the attention to detail in the building shell’s design and construction, as well as the extremely high quality of the windows and doors.

The structural insulated wall panel systems (SIPs) have many advantages when creating a well-insulated and air-sealed building shell that is cost effective to produce. The panels we chose to use on the prototype are 6-inch thick urethane panels, that are 4 feet wide by 24 feet long, factory manufactured and pre-cut by Winterpanel in Vermont. The most significant advantage of the SIPs is that they provide an uninterrupted thermal barrier for the shell that is also a durable and easily sealed air barrier.

The Passive House requirements for a building’s shell are very specific. To qualify for Passive House Certification, a building should not have any thermal bridges in the foundation or building shell, and the building, when complete, must meet strict air sealing requirements verified by a blower door test. The SIPs system has allowed the prototype’s construction to conform to these Passive House requirements, while still allowing for simple and cost effective construction.

The second advantage of the SIPs system has to do with the size of the panels and the ability to have them factory pre-cut to fit each building design. These benefits are maximized by utilizing our computer designs in the actual production of the construction components. By utilizing advanced three-dimensional computer models, we are able to coordinate all the expensive building shell components (including windows, SIPs and structural frame), and then incorporate the computer’s accuracy in the actual construction process. By putting emphasis on planning and leveraging that in the construction, we can improve the speed, accuracy, and quality of the site work.

One frequently asked question regarding SIPs panels is the environmental impact of the foam insulation used in the panels. The three standard foam types used in SIPs panels are urethane foam, and Expanded Poly Styrene (EPS). We choose to use urethane foam for the prototype’s panels because it has a higher R-value per inch, resulting in a thinner panel and a higher total R-value per unit cost. The criticism of this foam type is that the R-value decreases over time. The total aged R-value of the urethane, however, is still higher than the comparable EPS R-value per unit cost. While both foam options are considered green products according to the USGBC, it has been suggested that the EPS production is more environmentally friendly of the two foams. G•O Logic has used both foam types and considers their application on a case-by-case basis.