So, again, for this next house, we are going for Passive House Certification, which is still fairly new to the States, but has been around Germany for quite awhile. A quick refresher: Rather than just being a points based system like LEED or Earthcraft, Passive House sets rigid standards that must be met both by computer modeling of the building and verification and testing in the field. Rather than relying on fancy and expensive systems like geothermal heating or solar hot water, the focus is on super insulation, airtightness and controlled fresh air. One of the ultimate goals of Passive House is to have a home that uses 10% of the heating and cooling load of a normal house.
One of the biggest factors in achieving this is the windows. We ended up going with the 525 series by Serious Windows for a number of reasons. First, and most important, we are able to meet the Passive House standards with these windows. It’s a combination of the window being triple pane and the thoughtful construction of the fiberglass frame. When you look at the specifications of most new windows, they show the U-value of the window (which is the inverse of the R-value and refers to the thermal quality of the window). However, this U-value is sometimes just the glass, and doesn’t take into account the whole window, including the frame. When you get windows with really high performing glass, the frame of the window becomes the weak point in the window. The Serious 525 series has a whole window U-value of .22 (4.5 R-value) for the casements with high solar heat gain coefficients that we are using.
Serious has even higher performing lines of triple pane windows, but we are working with a modest budget. Ultimately, it came down to price as other European and Canadian brands were just not affordable to us. Even with Serious, we are paying about 65% more than what we have been spending on the Pella Proline series, which we have been really happy with in all our other houses. Honestly, if this was one of our spec houses, I don’t think I could afford to pull the trigger on these windows at this point because of the price as I unfortunately don’t think the market values all these energy savings though I’m hoping that will change.
The price of these windows was really the biggest moment of pause for us on whether to continue with Passiv House. We calculate the payback as taking at least 20 to 25 years versus going with the Pella Proline, which is a long time. But, there a few other advantages and cost savings because of these windows. One benefit is the potential for condensation on the insides of the windows from relative humidity should be cut dramatically down. Another is the increased comfort level of hanging out close to the window and not feeling that temperature difference that you might feel with a double pane in the middle of winter. Coupled with the tightness of the house, the super insulation, and the ERV system, we are able to drastically reduce our heating and cooling load and go with a much more inexpensive hvac system.
Another cool aspect of the Passive House standard is that through modeling you actually spec different glass for different windows based on location. Initially, this sounded really forward thinking and intuitively made sense as you would want a higher solar heat gain window on the south side, but not the west, to actually have the sun warm the house in the winter, but not overheat it in the summer.
Interestingly, the orientation and specs of our house dictated that we need high solar heat gain windows on all of our windows (SHGC=.40), which turned out to be a blessing. For, you get much better visible transmittance with the high solar heat gain windows. The 7, 9 and 11 series Serious windows can have either a blue or greenish tint to the glass and is noticeably darker. This really catches your eye when you have two different types of glass in the same room, which we would have had because of the open floor plan.
Overall, I think we have always tried to strike that balance on our houses of having strong passsive solar orientation while still taking into account privacy, views and aesthetics. For us, it’s usually a bit of compromise when building in town on gridded infill lots. My big take away from this experience thus far is starting to take into account the glass to frame ratio of the windows we use. For example, it’s much more efficient to have one giant window rather than two smaller windows of the same area as the glass to frame ratio is usually better with one big window. Anyway, yet another consideration to throw into the mix when designing future houses.
I’ll probably ramble on a little bit more about the Serious windows when we get them from Colorado in another month or so.