Winter is coming – “R” your windows ready – R values and window coverings

Tell Your Friends

deanna-cellular-shadesEven new windows are the biggest source of lost warmth from the home.

The laws of nature teach that heat moves towards cold. This means that in the winter, the toasty warm air in your home is seeking to free itself through your windows and in the summer, that oppressively hot air outside is seeking to enter your cool interior through those same windows.

Since 20% of the average traditional home’s exterior square footage and up to 40% of a contemporary home’s square footage is comprised of windows, the need for insulating theses windows becomes evident. Insulation is simply a product of dead air space, so even a basic roller shade provides a significant improvement in heat loss by creating a thermal layer between the window and the window covering.

How “R” we going to decide which window coverings will provide acceptable insulation?

To make the best decision, we need a standard form of measurement to determine insulation effectiveness. The standard we will use is the R value. The R value is simply a measure of the resistance to heat flow through a given material. The higher the R value, the greater the resistance. I have always hesitated to quote R values of window treatments because they are typically derived in a laboratory rather than a real world environment. To determine R values, the window covering is secured on all sides over a frame in a controlled environment lab. In the real world, the window covering has gaps on the sides and bottom through which the air can flow. In the real world, the window and covering are also subject to significant changes in humidity and temperature throughout the day, not so in lab testing. So, I use R value not as a value I would bet my first-born on, but as an accurate representation of how one product can be predicted to function relative to others. With that said, here are window coverings in the approximate order of their ability to resist heat flow.

Thermal board – attached on 4 sides – r 11.5

Insulated Roman shades r 2.5-r 7.0 depending on number of layers

Double cell blackout shades r 4-r 6

Double cell light filtering shades r 2.1- r 3.6

Shutters r 3.4

Vertical Blinds r 3.2

Wood Blinds r 3.o

Aluminum Blinds r 2.8

Allow me to state the obvious. The above values are only accurate when the blind, shade or shutter is in the fully closed position. If you are a light freak like me and open your window coverings first thing each morning to allow the glory of the day to come in, you eliminate the insulation values. So, although a quilted shade or blackout cellular will give great insulation when down, your rooms will look like a cave.

Stay warm my friends!