The right window treatment can give your passive energy conservation efforts a huge boost. Window treatments can include see-through solar shades and reflective film to cut down solar gain in hot climates, or thermal drapes and honeycomb fabric shades to fend off winter heat loss. Ideally, window treatment design should do both for maximum impact on heating and cooling costs. Manufacturers have created a wide range of specialized materials to help homeowners design energy-efficient window dressings, so it isn't quite as difficult as it once was to produce a beautiful window that also saves resources.
R-value is the number manufacturers use to measure a material's ability to resist heat transfer. It's useful to look at R-value when shopping for window treatments, as those that are intended to help conserve warm or cool air inside your home will often be labeled with their R-values. A higher number is better than a lower number. Total R-value of a window space is the sum of the R-values of all the layers of material, from the inner blinds, through the window and out to the window film, if any. Even the air trapped between layers of window dressing contributes to the total R-value.
You can use nearly any combination of drapes or blinds that appeals to your decorator sense, so long as you follow a couple of basic principles. To get maximum insulating value out of drapes and blinds, hang them so they touch the window frame but not the window. This placement creates an air space between the window and window treatment and "seals" the barrier air into the space, so your warm air isn't flowing in to be cooled against the window. Hang blinds or short curtains inside the frame so they touch all four interior sides of the frame. Drapes should hang at ceiling level or with a box at the top to trap air and actually touch the floor at the bottom to prevent cold air from flowing out from under them. They should rest against the window frame. Roman shades and roller blinds come in every shape and size, and an increasing number are available in insulating materials, such as honeycomb fabrics that use tiny air spaces to increase R-value.
Hot weather defenses revolve less around heat transfer through materials and more around preventing solar gain. Light penetrates window glass to become heat on the inside, where it tends to build up. Window treatments to combat solar gain either block sunlight or reflect it back out. Great strides have been made in creating materials that reflect and still allow a view out. For instance, roller-type window shades that look like screening made of natural fibers are actually reflective and allow you to look outside while turning back sunlight. Others are solid with reflective coloration on the outward side and decorator colors facing in to complement your room. You can use blackout draperies or a combination of lacy curtains and wooden interior shutters that you can adjust to suit your light needs. Fill your window frame on the inside with bamboo roll-ups, and dress up your look with simple muslin tabbed curtains to match your furniture.
Interior window treatments do their best work in winter --- keeping warmth inside --- but R-value can lose the battle with solar gain in the summer. It will help immensely for you to cut or eliminate sunlight that directly falls on the surface of the window. Your many options for this include reflective window film, awnings, shutters, solar window screens, shade covers and exterior blinds. Solar window screens exclude insects and allow you to see out, just as conventional screens do, but reflect back 60 to 90 percent of the sunlight that would have hit your window. Reflective film can be applied inside or outside your window, and some brands even increase R-value slightly.
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