Sliding Window

Also called a sash window, sliding windows can be opened by sliding a moveable 'sash' horizontally or vertically within the frame. A single hung window has one moveable sash, while double hung windows can open each sash.

Sliding windows can cover large openings, but they are not as energy-efficient. Consider substituting a casement or tilt-and-turn window for the opening part, and a fixed window for the rest of a large area, so you have both fresh air access and the big view.

Look for the Energy Star window rating label in North America. It contains these factors for windows:

• U-value (inverse of R-value) measures how fast heat flows through, so lower U-value is better)
• Solar Heat Gain Coefficient (SHGC) measures how well the window transfers solar heat energy
• Air leakage (lower is better), and Energy Rating (ER - dimensionless) is a combination of all those factors (higher ER is better)

Excellent U-values are around 1 W per sq. m per degree (equivalent to R5), and excellent ER ratings are above 35.

Sliding windows have a higher tendency to leak air, so are typically not as energy efficient as casement windows. When the weather stripping gets damaged, they are also more prone to leaking in water.

The most basic window is, of course, merely a hole in the wall to let in light and air. Different materials have been used over time to fill window openings to let in light while keeping out insects, animals, rain, and wind. Before glass became widely manufactured, translucent materials including paper, animal hides, flattened animal horn, and even thin slices of marble were used as window panes.