The foam insulation board in covered with GreenGuard RainDrop house wrap. This is a robust building paper that has built in micro drainage channels to provide a passage for any water that might get behind it to migrate down and out.
Finishing the exterior system continues with placement of the 2” of XPS foam on the exposed exterior walls. This insulation is installed outside the Perm-A-Barrier membrane and will (theoretically) prevent moisture condensation inside the wall cavity as it moves the “dew point” outside the wall. It will be wrapped with “Green Guard” building paper, mainly to protect the foam from UV degradation. Vertical 1x4 battens of composite wood, Hardy Trim, will go on top of that to mount the clips for the interchangeable metal shingle rain-screen system.
Our firm is committed to achieving a number of major efficiency certifications, most difficult of which is the German standard called PassiveHaus. There are so many things you could say about PassivHaus, but essentially the idea is to use an extremely small amount of energy to heat your house through three measures: 1. super-insulation 2.eliminate air infiltration 3. heat the house with solar heat gain and ambient heat from people, lights, ect.
One of the major components for controlling these three factors are windows and doors because these are the weakest points of the system in terms of insulation value and air infiltration as well as the strongest points for gaining some solar heat. So, what do we look for in windows for the design of a passivhaus?
- The windows should have at least two gaskets and a mechanism that firmly engage these gaskets when the window is closed. These gaskets insure quality air infiltration resistance by sealing the opening not unlike a door on a washing machine.
- The windows should have as high an insulation value as possible in both the frame and the glazing. The highest quality window has a U value of .12 to .15 or R value of 8.33 (American Standard). This insulation value, of course, is used to keep the temperature extremes of the outside environment on the outside. Without buying German windows and glazing, the absolute best “normal” window can only render a .24 U value. What it takes to make this insulation value is pretty amazing. The glazing sandwich is three layers of glass covered with a specialized film and separated by two layers of a noble gas such as argon or krypton.
- Windows should be thermally broken. Windows achieve a thermal break as much as they can in a couple of ways. First, insulation covers up the window frame as much as possible lowering the effects of external temperature. Second, there is a physical break with an insulative material between the inside frame and outside frame.
- Windows should be reasonably priced. When I say reasonably priced, this is a relative decision. I think in many ways that quality (but inexpensive) vinyl windows, if given a chance, could meet PassivHaus standards in the overall system. For example, we have a window that is a casement window mulled to a fixed glazed panel. It’s a fairly big window. Initially, we had an estimate from Pazen which came in at about, say, $2,500 plus shipping. Optiwin, arguably the best window made, we didn’t even price. We priced an American equivalent called Jeld-Wen which is beautiful and high performing. It came in at 30-40% less than the Pazen. Now we’re talking! Next, we priced the mid range Sorpetaler, a German window, which has somewhat better performance than the Jeld-Wen. The price came in 50% below the Pazen not including shipping. If you include shipping, then the Jeld-Wen is arguably the better choice for an American Market.
- Windows should be locally sourced. If energy consumption is an issue, then it should definitely be better to source locally, right? Possibly not. Why? According to Bronwyn Barry, a PassivHaus window expert at Quantum Builders in Berkeley, CA, because Sorpetaler are shipped by rail and ship to where we are in San Francisco, the carbon footprint is almost as low as shipping from Oregon by truck (Oregon is where Jeld-Wen windows are made). I think this debate will be up in the air for some time, but Ms. Barry has some pretty compelling data to back this up.
Here’s a German window company making some of the best windows on the planet. Expect long lead times, though. 4-5 months.