Green Windows & Doors Resource
From a green-built standpoint, windows rank second only to the design of an HVAC system in overall technological complexity. Heating, cooling and lighting consume 67% of all the electricity that’s generated. Windows and doors comprise a large portion of heat loss in a wall and lower the overall R-Value of the wall. Installing windows and doors correctly will help eliminate air infiltration and water leaks.
See Chapter 7 on Windows & Doors in the Green from the Ground Up book for more details or contact us about training.
Window Energy Performance
There are three primary factors in a window’s energy performance:
- frame construction
- spacer material that separates individual panes of glass
- through the glass (by radiation)
- across the spacer material that separates the two glass layers at their edges and through the frame of the window (by conduction)
- through the movement of air in the space between the glass (by convection)
- between the moveable or operable frame components (by air leakage)
Rating Windows for Performance
The National Fenestration Rating Council (NFRC) was formed to standardize the claim of energy efficiency by window manufacturers.
U-factor – for the entire window, distinct from a center-of-glass rating.
Solar heat gain coefficient – represents the amount of heat that is transmitted through the glass. The lower the number, the less heat transmittance.
Visible light transmittance – is the “sunglasses” effect. The lower the number, the darker things will appear through the glass.
Air leakage – is rated in cubic feet of air passing through a square foot of window area. The lower the number, the less air will pass through cracks in the assembly. This may be left blank by manufacturers of lower-quality windows.
Condensation resistance – measures the ability of the window to resist condensation on the inside of the glass. The higher the number the better.
Green Window & Door installers’ Transition Guide
Familiarize yourself with which windows are available in your area
Learn about what technologies are available to market to your customers
Many manufactures and dealers offer training and free seminars
Consider wood windows
High quality and long life
Available in replacement sizes and installation
More expensive than vinyl, Use FSC wood or engineered materials
Carefully install windows and door to eliminate any air leaks
Even a small air leak can have a huge impact on heat loss over the life of the building
Use expanded foam around all windows and doors. Be sure that head flashing is installed
One can of expansion foam. Look for products that use HFC rather than HCFC or CFC as propellants.
Understand the prevailing winds on the site
Wind will push on a building and contribute to air infiltration. Understanding the prevailing winds can also help you to take advantage of cooling breezes
Information is available from the national weather service. Visiting the site is also very important. Talk to someone who is familiar with the area if that is feasible
On a colder, windy site, windows and doors should be located on the leeward side of the building. In a warm climate, locate windows and doors to allow breezes to flow through the home
Install different windows types based on building orientation
Windows on the South side of the building should have high solar heat gain and windows on the east and west walls should have low solar heat gain
Passive homes use the sun to help heat the home in the winter. Awnings and trees help shade the sun in the summer.
Talk to your local window manufacturer about what’s available. Learn about low-E glass and its benefits.
Choose windows and doors made from FSC certified wood
FSC wood comes from sustainably managed forests that replant trees that are cut down.
Not available everywhere
Contact your local window manufacture and ask for FSC materials.
Replace all existing windows with the best windows your customer can afford
Windows are expensive, but encourage you client to spend more upfront on windows in order to save more on energy and be more comfortable over the life of the home.
Donate the removed windows to a local salvage yard. Some windows can be deconstructed and recycled.
The window manufacture will have information on the U-Value of the window. The lower the U-Value, the better the window.
Explore super windows
Equivalent of an R-7 or higher by using the best available glass packages (triple glazed, gas filled) in the industry for insulation, strength and security. Unparalleled construction and durability
These windows need less maintenance and are very long-lasting.
Expensive and not available everywhere. Available in Canada.
Green Building Training & Certification
Find out when the next Green Building Training is and learn more about Green Building Practices.
Read more on the Federal Tax Credits for Windows & Doors
Exterior Windows and Skylights
- U factor <= 0.30
- SHGC <= 0.30 30% of cost, up to $1,5002
- Not all ENERGY STAR labeled windows and skylights qualify for tax credit.
- Meets IECC in combination with the exterior window over which it is installed, for the applicable climate zone
- 30% of cost, up to $1,500
- Manufacturer Certification Statement will list classes of exterior window (single pane, clear glass, double pane, low-E coating, etc.) that a product may be combined with to be eligible in specific climate zones
- U factor <= 0.30
- SHGC <= 0.30 30% of cost, up to $1,500
- Not all ENERGY STAR doors will qualify.
In combination with a wood door assigned a default U-factor by the IECC, and does not exceed the default U-factor requirement assigned to such combination by the IECC. 30% of cost, up to $1,500
Green from the Ground Up Best Practices
- Invest in high-performance, low-e glass to improve energy efficiency
- Avoid plain wood frames in favor of wood clad with aluminum or vinyl, or consider high-quality PVC or fiberglass for longer life and lower maintenance.
- Choose multi-pane designs filled with argon and krypton rather than air to minimize heat loss through convection.
- In passive-solar designs, install high solar gain windows on south-facing walls to reduce energy costs
- Read Nation Fenestration Rating Council labels carefully and choose windows appropriate to the climate and overall house design
- Avoid single-glazed skylights
- If possible, plan an entry “airlock” to reduce heat loss.
- Detail flashing around doors and window to reduce the risk of water leaks and seal the gap between window and doorjambs and framing members with expanding urethane foam to eliminate air infiltration.