A pelmet (also called a "cornice board") is a framework placed above a window, used to conceal curtain fixtures. These can be used decoratively (to hide the curtain rod) and also help insulate the window by preventing convection currents. It is similar in appearance to a valance, which performs the same function but is made of fabric. A pelmet can be made of plywood, and may be painted, or fabric covered.
The convection currents mentioned are illustrated below with red arrows representing warm air and blue arrows representing cold air. The thick black lines are the wall and floor, the Yellow wavy line is the curtain, and the short, thin black line above the curtain is the curtain hanger.
Without a pelmet, what happens is this: Heat is radiated through the window as shown by the short, red arrows. This results in cold, heavy air falling to the floor, which creates negative pressure. Warm air is then drawn down from the ceiling to take its place. This warm air is cooled and the cycle continues. The entire room becomes a convection current fueled by the heat loss through the window. Not good for energy efficiency.
A pelmet (shown in green) breaks the convection cycle by creating a physical barrier to the air flow. The cold air next to the window does not sink and pull warm air from the ceiling. Genius! Thank you Mr. Pelmet.
Here is the pelmet we installed in the lounge. It is made from a beautiful old piece of exterior weather board mounted into the lintel.
We are using a different approach to pelmets in the kitchen, dining room and bathroom. I'll write about those in another post.