Windows

So one of our most recent preoccupations has been windows. In a well insulated house, windows are the gaping holes out of which all of your heat pours in the winter-time. (In a poorly insulated house, the heat pours out everywhere, including your windows.) This can be mitigated a little by investing in double or triple pane windows, filled with a low heat transmittance gas, such as argon.

For ease of maintenance, durability, and thermal properties, we are hoping to use fiberglass framed windows in our house. I just got a quote from one of the local building supply places in town, and the fiberglass windows seem to be in the same range as the aluminum-wood windows we had originally budgeted for, and maybe even a little cheaper.

Why fiberglass? Well, for windows, there are basically 4 options -- wood, vinyl, aluminum, or fiberglass, (or a composite of one of the latter 3 with a wood interior). The glass portion of the windows is basically identical from one type to another (or at least it can be if that's what you specify). Of the four, aluminum has the poorest insulating value as a material. They make pots and pans from aluminum precisely because aluminum is an efficient conductor of heat, not exactly what you might want when it's cold outside. To try to fix this, they engineer thermal breaks into the window frame to prevent your hard-earned heat from conducting directly to the outside, but it's still the worst performing of the bunch.

Wood, as far as structural materials go, is actually a decent insulator, but wood windows require a significant amount of maintenance over the long term, and are the most susceptible to water damage.

As for vinyl, they share a common problem with wood and aluminum: expansion. Just about every material expands and contracts when exposed to different temperatures, glass included. Windows depend on a proper seal between the glass and frame in order to have any insulating properties at all. Both vinyl and aluminum expand at different rates than glass does, leading to relative movement between the pane and frame which could eventually compromise the seal. Wood actually expands and contracts in relation to relative humidity levels much more than temperature, leading to the same types of issues. Fiberglass expands at almost the same rate as glass, so the potential for a seal compromise is greatly reduced.

After all this, what kind of R-values are we getting out of windows? If installed properly, and sealed well with no air infiltration, most double pane windows regularly available are between R-3 and R-4. Doesn't seem like so much compared to R-40 walls, huh? Well, the formula isn't quite so simple, because on sunny days, windows can function as a source of heat for the house, if oriented correctly. On our design, we have used large windows along the south of the house, and tried to use east and west windows sparingly. We have actually managed to eliminate all windows on the north side, which gets little to no direct sun exposure. As soon as the sun goes down, however, all windows function as energy sinks for the house.

In the house we are currently renting, the windows are equipped with properly sized window quilts, which are drawn over the window at night during the winter to help insulate the windows a little more. The quilts are kind of a pain to use every night and morning however, particularly since you have to roll or fold them up by hand. We will definitely have some form of additional window insulation for winter nights in the Little House in the Big Woods. They sell cellular shades which have insulating properties, Mindy could make us some window quilts (hopefully corded somehow, unlike the ones we used this past winter), or I've been thinking about some sort of interior shutter that could be latched shut at night. Curtains, especially thick ones, also offer some protection, although they generally allow more air back and forth around the edges than the other treatments mentioned. Since the exterior walls are over a foot thick, there would definitely be room for some insulation in front of the window, it's just a matter of coming up with a system that is relatively easy to use. After all, if window quilts are a major bother to let down and put up, then they will not be let down as often.