With so many types of window treatments available, including awnings, shades, storms, and shutters, it's hard to know which one is right. GreenSpec can help.
Awnings are a traditional way to control solar heat gain in the American South. Blocking gain is more effective than dealing with the heat after it comes into the building. However, awnings aren't the best product for every window in every climate.
Most window attachments are chosen with aesthetics in mind--probably in part because picking the right awnings, shades, shutters and other attachments for their performance characteristics hasn't been simple in the past.
In collaboration with BuildingGreen, publishers of GreenSpec, Lawrence Berkeley National Lab (LBNL) has been doing modeling, field-testing, and lab testing to develop standards for window treatment performance. Different types have different strengths, including glare control, thermal performance, and even security, so choosing a particular window attachment depends on your priorities. While performance is likely to be the foremost concern for most people, some products use materials with environmental health and safety concerns.
With the exception of window film, there is no performance standard to measure window attachments, so we eagerly await the results of LBNL's work. In the meantime, we've handpicked a number of manufacturers and products to list in GreenSpec that we consider best-in-class. In selecting these listings we looked for companies emphasizing strong performance and offering solid performance information (including some companies collaborating with LBNL), and companies with well-thought-out, innovative, and well-detailed products.
Read on to learn more about how to choose products that won't harm you or the environment.
The main advantage of awnings is that they block the light before it comes through the window, preventing glare, heat gain, and damage from UV-rays, while fully maintaining the view to the exterior. Keeping direct sunlight off your windows keeps solar heat gain out--which is a more effective strategy than trying to keep the solar heat after it has hit or entered the window. For times when you want the sun's heat, retractable awnings are available.
GreenSpec lists four awnings product lines. Awnings can cost several times as much as other window treatment options, so keep that in mind when shopping around.
It is common practice to treat exterior fabrics with fluorocarbon-based coatings for durability. Fluorocarbons are considered potentially hazardous to the environment and human health, so GreenSpec encourages both consumers and manufacturers to look for alternatives.
Exterior Sun Control Devices
Exterior roller shades, roller shutters, and solar screens are other options that block direct sunlight before it enters your home.
Roller shades are opaque or translucent, and when rolled down do not afford a direct view of the exterior. They are also commonly treated with PVC coatings, and GreenSpec encourages the market to find alternatives. Roller shutters provide lighting conditions closer to blackout and can also provide security and hurricane-resistance.
Solar screens are panels or roller shades and are designed with openness factors to allow direct views, even while covering the window. As with awnings, thermal performance primarily comes from preventing direct sunlight from entering through the window. Based on strong performance, innovation, and other factors, GreenSpec chose 23 products to list here.
Low-e, airtight storm windows provide a significant layer of thermal performance on the exterior of the window. They also afford direct views to the outside. Most exterior storm manufacturers use metal frames, although PVC frames with superior thermal performance are available.
In both cases, GreenSpec has concerns about the product composition--aluminum because of energy intensity, PVC because of life-cycle health and environmental concerns--but reducing energy use and good performance is the trump card. With that in mind we list six exterior storm products with good detailing and low-e coatings that can help bring an entire window up to near-high-performance levels.
Interior Window Panels
Interior window panels, like exterior storm windows, contribute to thermal performance and air tightness. Sometimes called "interior storm windows," these usually have frames made of aluminum, although magnetic strips and PVC frames are available. While some options can be moved up and down, many are fixed in place and limit window egress. Do not use these options in fire escape locations.
GreenSpec lists eight companies here, all of which pay attention to airtightness and usability.
Surface-applied films and seasonal flexible film kits provide reduced solar heat gain and increase the thermal performance of windows. Seasonal flexible film kits are primarily used to reduce convective and conductive heat loss through windows. For seasonal kits, aesthetics and short service life are downsides, though ease of installation and relatively low cost are upsides.
Surface-applied films, primarily used to reduce solar heat gain, can be compared using NFRC ratings, and from among these GreenSpec chose seven to list.
Interior Window Treatments
Blinds, curtains, drapes, shades, and quilts offer some thermal insulation, glare control, and solar heat gain control, although direct sunlight comes through the window before hitting the shade. Cellular shades, offering superior thermal performance, and interior solar screens, featuring PVC-free fabric since durability is less of a concern on the interior of the window, are both attractive options.
With an emphasis on strong thermal performance data--when we could find it--GreenSpec lists 20 products in this area, including products such as light shelves that extend the reach of daylight to the interior.
Our approach in creating this guidance has been to try to answer the question, "How can we make our windows work better?" In many cases, window restoration should be among your first choices. Proper truing and gasketing can drastically improve airtightness and make windows easier to open. Lead paint management is important to consider in the case of older windows. GreenSpec chose five reputable window restoration firms to list.
So...What's Your Answer?
The proper choice for window attachments varies from case to case--there is no one-size-fits-all answer.
Depending on the problems you face, your financial constraints (keep in mind that springing for a pricier window attachment may come with a quicker return on investment), and your design preferences, each option has its own benefits and drawbacks. For a more detailed exploration into each of these areas, as well as some representative listings, please see the appropriate GreenSpec section.
Comprehensive guidance is also available in our EBN feature article, "Making Windows Work Better." (As with most of our feature articles, BuildingGreen members can get continuing education credits for reading it and taking a short quiz.)