Openable and Non-Openable Windows

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Windows have undergone a huge number of advances over the last few decades. While most construction methods and materials have remained the same, windows have changed from heat-sucking drafty holes to efficient light-capturing devices which help improve energy efficiency.

Modern windows come in an enormous variety of shapes, sizes and designs. For most home owners, the aesthetics and cost of a given type of window are the most important factors in the purchasing decision. If you're building a passive solar home, those factors need to move lower on the list, though they can still be important.

The most important factor in window choice is its mechanics. All windows have three parts: the glazing, the frame and the sash. The sash holds the glass in place and the frame holds everything in the hole in the wall. The mechanics of each type of window determine how the sash moves, if it does.

All windows fall into two types: openable and non-openable. The latter category is obviously a lot simpler: it is a frame with a piece of glass in it, with no moving parts. Non-openable windows are cheaper than those which open and are also more energy-efficient, since they reduce air filtration to a bare minimum (almost zero if professionally installed).

Types of windowOpenable windows are more complex. Here is a quick list of the most common types:

  • Single-hung and double-hung windows (or "sash windows" in the UK) are two of the most popular choices. A single-hung window consists of two panes in separate sashes, one of which is fixed while the other slides. The two sashes are offset, one behind the other, so that the movable pane (the lower one) can slide up and down, opening the window. In a double-hung setup, both sashes move.
  • Slider windows are also popular. They are designed in the same way as double-hung windows, but the sashes are installed horizontally instead of vertically. The two panes slide left and right, offset as before, to open the window.
  • Casement windows are the most popular type which use hinges. In this setup, the sash (or sashes, if there are two) is hinged on the side and swings open, like a door.
  • Awning and hopper windows are like casement windows, but usually have a small hinged and a large non-opening sash. Awning windows are hinged at the top and swing open (usually outwards) with a space at the bottom, while hopper windows are hinged at the bottom and swing open (usually inwards) with a space at the top.

To be honest, the choice between the different window types is mostly a matter of aesthetics. All openable windows allow significantly more air filtration than non-openable windows, even when they are closed, and they all create ventilation necessary to cool a passive solar home. The only window type which differs from the others is the casement window, which not only allows ventilation but can also act as a wind scoop, funneling air into the house.

In general, you should only use as many openable windows as you really need. All the others should