Since we are trying to save money by doing as much of our own construction as possible, it means we absolutely must pay attention to details. Yes, we have subcontracted out many things: cement work, plumbing, electrical and much of the roof. But I guess we are considered our own general contractors because many of the big decisions and much of the precision are, generally, left to us. Making these choices and ordering the correct items in terms of type and size requires a great deal of research, and this is one of Scott’s fortes. Our windows are a prime example.
As mentioned earlier, our plans called for Loewen Windows, but Scott’s research convinced us to purchase Serious Windows. When ordering windows, three factors come into play: U-factor, Solar Heat Gain Coefficient (SHGC) and Visible Transmittance (VT).
According to The Efficient Windows Collaborative, U-Factor is the rate of heat loss of a window. The lower the U-factor, the greater a window's resistance to heat flow, hence, a better insulating property. (This is similar to the R-Value in walls and roofs.) High-performance windows have a U-Factor of .30 or lower. All of our windows with the exception of the three pictures windows on the south side of the house have a U-Factor of .18. The pictures windows have a U-Factor of .23.
The Solar Heat Gain Coefficient or SHGC is the amount of solar radiation that passes through the window and heats the house. SHGC is indicated with a number between 0 and 1. The lower a window's SHGC, the less heat is admitted into the house. Except for the picture windows, all of our windows have a SHGC of .21. On the south side of the main living space of our house, the eaves will prevent sunlight from shining directly into the house in the summer. However, they are designed to allow sunlight to enter the house in the winter in order to heat the house. Therefore, the SHGC of the picture windows is higher —.50. This higher SHGC also means that heat will escape at night. To prevent this from happening, we'll use insulating curtains on these windows in the winter.
Visible Transmittance (VT) is the amount of visible light that comes through a window. Most VT values are between .30 and .70. Higher VT values maximize daylight and view. The VT on all windows except the picture windows is .4. Since our view is to the south, the picture windows have a VT of .64. More light to see our world.
Just like good glass, it’s amazing what a lot of research will reveal.