energy efficient Windows and Skylights
Although exterior windows and skylights are a part of a homes envelope they play a much different role than insulated roofing and walls.
Windows for the home are a key component as they interact between the indoor and outdoor environments all the while allowing light to enter the home. They also react to sunlight, wind and occupant uses within the home. So in order to create a green home choosing the proper windows and skylights is an integral part of your green design.
High Performance Rated Windows and Skylights
A sure way of improving your energy efficiency in the home is by replacing old windows with new high performance rated windows and skylights. Windows, doors and skylights are all rated by two governing bodies ENERGY STAR and the National Fenestration Rating Council (NFRC). Canada measures their energy efficiency with the Canadian Energy Rating System (ER).
ENERGY STAR Windows and Skylights
ENERGY STAR is becoming a very well known international symbol representing environmentally efficient products world wide. Only manufacturers that create products that meet the standards set by ENERGY STAR will be granted this accredited label.
In order for a window or skylight to be approved by ENERGY STAR manufacturers must use several technologies to qualify.
ENERGY STAR Windows
Improved Framing - Efficient framing is important in reducing heat transfer. Wood composite, fiberglass and vinyl tend to insulate the best.
Low-E Glass - Special coatings/films are used to better reflect light. This helps to keep rooms cooler in the summer and warmer in the winter. More importantly they also protect us and our furniture from harmful ultraviolet light.
Multiple Glass Panes - Energy efficient windows need to incorporate at least two panes of glass. The air or gas between each pane helps to insulate. The more panes the more efficient and sound proof the windows become.
Gas Fill - A window that has multiple panes of glass also has a space in between each pane. This space can be filled simply with air however they can be greatly improved by filling it with argon or krypton gas. They are said to perform and insulate better than air. They are also odorless and non-toxic.
Warm Edge Spacers - These spacers can be made from fiberglass, foam or steel and are used to reduce heat flow and prevent condensation.
ENERGY STAR Skylights
Skylights are also subject to the same technologies that are available for windows today. It is even more important to find very high quality skylights as they are even more directly affected by temperature differentials.
National Fenestration Rating Council (NFRC)
The NFRC is a volunteer rating system that also provides necessary energy efficiency performance information on windows, doors and skylights. What is fenestration? According to their web site fenestration is "e;any opening in a building's envelope including windows, doors and skylights."e; Their rating system is more stringent than ENERRGY STAR's and they also use a different label.
The NFRC takes into consideration the following:
- U-Factor - This factor measures how well a product prevents heat from escaping the home. The lower the u-factor the more efficient that product is.
- Solar Heat Gain - This measures how well a window, door or skylight blocks the heat from the sun. Again the lower the number the more efficient the product is
- Visible Transmittance - This measures how much light can be transmitted through the product. The higher the number the more daylight you will receive through your window or skylight.
- Air Leakage - This is a measurement that determines how much outside air can enter the home. The lower the number the better the product. This is an optional rating and is not often on labels.
- Condensation Resistance - This measures how well a product resists condensation. The higher the number the more able the product is to resist condensation. This is another optional rating for manufacturers.
- R-values - a measurement of a product's resistance to heat loss. Materials (floors, walls, and roofs) with higher R-values are more energy efficient. R-values are still used by many building materials, especially insulation.
The NFRC also takes into account the other technologies available to manufacturers that are required for ENERGY STAR qualified products.
Types of Windows
There are typically two types of windows, operable and fixed.
This style of window is the least energy efficient of the two. An operable window is one which can open of course and there are many styles; horizontal/vertical sliders, single/double hung, turn and tilt etc.
If purchasing an operable window be sure that it meets the highest possible standard for air tightness to improve your energy efficiency. It is recommended to only install Operable windows when necessary however they are required by law on floors with bedrooms to provide an emergency exit.
Fixed windows are your best choice for energy efficiency as they are built with much better air tightness capabilities. They are also much more safe and secure.
Not only do high performance windows improve your energy efficiency they also help provide free natural daylight into the home. The more daylight provided by your windows allows you to use less electricity resulting in a reduction of your energy consumption.