Windows. Something we take for granted, right? Now I know differently. Many of you probably already know what I had to learn, but for any that are like I was - totally ignorant of the properties of that piece(s) of glass, here is my story.

Since I want to build a high energy efficient home, I better take care about how fill all those big holes in the walls, we call windows and doors. Florence County is in Northern Zone of the Energy Star Climate Zones, which means heating, rather than cooling requires most of our energy bill. Following are the guidelines for window efficiency. Note that Passive House is the GOLD standard for energy efficiency. I decided early on that I wasn't going to even try to attain that level - just the Focus On Energy Certified home. See my discussion of that under Energy Efficient Building.

U-Value is used with windows in place of R-value for insulation and it is simply 1/R-Value. So a U-value of .20 is the same as R-5 (1/.20 = 5). The smaller the number, the less heat the window will allow through -= both directions.

SHGC is Solar Heat Gain Coefficient is the fraction of incident solar radiation admitted through a window. So in the winter, I want plenty of solar heat to come in, but in the summer, I want very little. Ideally in my area this number would be between .40 and .50, with shading over the window in the summer. But to get that, I would have to buy very specialized windows which means lots of $$$. So not really feasible.

Air Leakage indicates how many cubic feet per minute of air comes through the window assembly itself at 20 pascals of pressure (25 mph wind). A very good friend of mine advised me to consider this number. When he built his house he didn't take air leakage into account and ended up regretting it. However, research on the internet says that anything less than .3 is really not measurable.

By visiting the home shows and talking to all the window vendors, I decided I wanted fiberglass or composite frames. First they are virtually maintenance free because they don't need painting and they are moisture proof. And second, they have very good numbers for low air leakage. That along with choosing casement windows, they are very good for energy efficient building.

Next decision was double pane or triple pane. Friends who put in triple pane said they are very glad they did. Other friends said they weren't worth the price. Who to believe - they were about 50% more money for not much difference in U-value. Translating to R-value, triple panes (that I could afford) were 4.5 R-value versus 3.4 for double panes. And they had lower SHGC value. What to do?

I ended compromising and going with Kolbe (made in Wausau, Wisconsin) triple pane Forgent Series (fiberglass) for the main level windows and sliding doors facing the lake and with Marvin (mode in Minnesota) double pane Essential Series (fiberglass) for the rest of the house. My logic was that the main level lake side has the most windows and therefore I wanted the lowest heat loss and air leakage. The solar heat gain is low so I won't benefit very much from heat from the sun in the winter. On the other hand, I won't lose much heat to the outside either.

Time will tell.