Add Value Through Energy Efficiency - Why R-Values Make a Difference
To help understand how window treatments, both hard and soft, can contribute to a home's energy efficiency, you need to understand R-values. Manufacturers refer to the R-value of a building material to describe it's resistance to transferring heat between two environments of differing temperature: the higher the R-value the better the insulation material. Fiberglass, for example, has R-values as high as 40. Windows, on the other hand, have the lowest R-values -- on average between .9 and 3.0. Even it a window is rated as energy efficient and is tightly installed, a significant amount of energy that transfers between a home and the outside occurs through it's panes. While double-paned glass and specialized glazings can certainly elevate insulation value, window coverings can improve thermal performance significantly more.
One of the first considerations when dressing windows in fabric for thermal protection, is lining. A three-pass blackout fabric for the backside and a heavy flannel interlining are crucial. These layers each have an R-value, as do the pockets of air between them. Some estimates indicate that this combination of lining and interlining improves a widow's R-value by as much as 300%,
Custom fit shutters, shades and blinds are additional layers that further contribute to a home's efficiency. Properly fitted, they create an isolating barrier right at the lass to reduce thermal exchange. Blinds are better at controlling heat gain in summer rather than heat loss in winter. Hardwood blinds have R-values of 2.77 to 3.17. Shutters have a similar R-value. Shades are year round insulators and most materials are available in either roller or Roman style of operation. The R-value will vary depending on fabric and construction from 2.6 to 5.0. Honeycomb shades are designed to trap air, with R-values between 3 and 4.8 or higher. Tightly woven natural shades report an R-value of 4.0 to 4.5. The R-value of fabric shades can vary widely depending on the fabric and the lining and interlining used, because as with draperies, the number of layers helps increase efficiency.