WINDOWS & DOORS
Windows, skylights, and exterior doors are common sources of air leaks and heat loss in our homes, contributing significantly to utility bills. Drafty windows, visible condensation, or frost build up are just a couple indicators that your current windows aren't performing well, although condensation or frost may also indicate high indoor humidity. However, before you jump to completely replacing your windows, there are window improvements that are both cost effective and can improve comfort.
New windows are expensive and can take many decades to payback; often, the payback period is longer than the life of the window itself! Unless the window frame itself is in poor condition, showing signs of deterioration, rot, and moisture leakage, you may benefit from simple improvements such as air sealing, adding storm windows, and replacing window sashes and sills. Read more about common myths regarding window replacement from the National Alliance of Preservation Commissions.
First, start by repairing any damaged window panes or cracked and rotted sashes. If you are replacing sashes, invest in higher performing glazing whenever possible. Next, make sure that every window closes and locks to get a tight air seal. Finally, add weatherstripping to any window that has small leaks. Since these improvement strategies don't address air leaking from around existing window frames, if you're refinishing walls or reinsulating, remember to seal & insulate around window frames at that time as well! Adding storm windows to single-pane windows is also a good investment.
However, if you need to replace your windows because they cannot be repaired, investing in efficient windows will help create a more comfortable indoor environment and provide a reduction in heating costs. Rebates may be available for window upgrades that can significantly help reduce the initial investment. Since replacing windows is an expensive remodeling project and the installation cost is the same regardless of type, the bottom line is buy EnergyStar rated NFRC windows.
The Efficient Window Collaborative is a good resource on decision making regarding whether to repair or replace your windows and how to make repairs and select replacements.
Installation
Like any other product you put in your home, selecting a qualified installer is vital. The entire exterior surface of your home is a barrier between the indoors and the weather, and windows should be integrated into that system. It is critical they be installed and flashed according to the manufacturer's recommendations to preserve the warranty and optimize the performance. Failure to properly flash a window installation can result is water inside your walls and may result in severe damage to your home and health. The install should not compromise the drainage plane created by the housewrap and flashing. Do your research and select an installer that has reputable experience and is willing to meet with you to answer questions. Ask friends and neighbors for referrals and look for local installers to minimize added transportation costs. Interview more than one installer to make sure you're getting accurate information and competitive bids. Always look for a contractor that will warrant their work and is willing to answer questions or concerns along the way.
Passive solar heating
In our heating-dominated climate, the largest windows should be located on south facing walls. Here, they capture the most direct sunlight which both provides for better indoor daylight and provides free heat from solar energy. By using wall and floor materials such as brick, concrete, tile or plaster walls that capture and hold the solar energy passing through the windows, you are implementing passive solar design strategies. In winter months, passive solar design can help reducing heating costs. To optimize heat gain, utilize windows with a SHGC of .4 or greater but maintain a U-Factor of .32 or less.
You don't want to increase your air conditioning costs in the summer, so to avoid overheating in the summer you must add shading devices such as roof overhangs or shade-providing landscaping. East and especially west facing windows are subject to overheating in the summer from direct sunrise and sunset solar radiation. Because the sun angle is lower during summer morning and evening, it is difficult to shade these windows, and west windows allow heat in during the hottest party of the day. Windows on north walls loose energy but offer a comfortable indirect source of natural light.Learn more about the details of window areas and orientation.
Storm Windows
Storm windows may dramatically improve the performance of you home by reducing heat loss and improving air tightness. They offer air sealing benefits that make them a valuable investment when window replacement is not necessary. Storm windows are available as either interior or exterior panes of plastic or glass. Both glass and plastic are available with coatings that can help improve visibility and performance. Interior storms tend to be more cost effective, convenient to install, and even perform better than exterior storms. Exterior storms require weep holes that diminish air sealing capabilities. Use caution when investing in exterior storms as over time, they can compromise the performance of the window they are protecting. Without proper drainage, trapped moisture can cause wood frames to rot and render the window inoperable. The table below describes benefits & disadvantages of types of storm windows:
| Benefits | Disadvantages | |
| Glass Storms | Better visibility
Longer performance life |
Heavy to install
Fragile More costly |
| Plastic Storms | Inexpensive Lightweight |
Scratchable/ easily damaged Yellowing & degraded performance over time Reduce visibility |
Like replacement windows, storm windows can be found with wood, vinyl, or aluminum frames. Performance of storm frames matches replacement window frames. Wood has good thermal performance but is susceptible to rot and thermal expansion/ shrinkage. This can make them difficult to install and results in air leakage. Vinyl also offers good thermal performance but can crack and warp under extreme temperature. It is manufactured using an environmentally detrimental process. Aluminum is very low-maintenance but transfers heat quickly. Combinations of materials, either vinyl or aluminum-wrapped wood frames, are available to optimize frame lifetime and performance.
Selecting New Windows
Before you start shopping, learn the components of a window. The performance window is determined by a combination of factors relating to the frame and glazing type . Start with windows that bear the Energy Star certification logo and then verify they are double glazed, low-E coated, and argon filled. This means that the window meets minimum U-factor and Solar Heat Gain Coefficient (SHGC) standards. However, these are not the only performance factors to consider. Next, look for the NFRC label. Windows are tested and certified by the National Fenestration Rating Council (NFRC), this label will describe all performance values of the window. Your replacement windows should, at a minimum, meet the following requirements:
- U-factor: .32 or less, lower is better
- Solar Heat Gain Coefficient (SHGC): .30 to .60, depending on location, you may want higher or lower SHGCs. Higher SHGC values are preferred on southern walls if using passive solar design
- Visible Transmittance (VT): .50 or more, higher VT values transmit more light
Doors
The first place to save energy on doors is by maintaining them. In particular, weatherstripping around doors wears out quickly; replace it as often as necessary. Adding storm doors or replacing old, uninsulated exterior doors can add to the efficiency of your home. Like windows, invest in the most efficient doors you can afford. Install new doors so they are square and seal tightly. Add expanding foam insulation around the frame and rough opening to ensure there will be no air leakage. Polyurethane-filled steel and fiberglass doors insulate better than solid wood doors.
Glass patio doors or even doors with glass lites (windows) should have Low-E coatings to improve their thermal performance. Especially with patio doors, look for multiple-paned glass and consider swinging doors over sliding style. Sliding doors do not seal as tightly and weatherstripping wears quickly resulting in leaking air.
- National Fenestration Rating Council (NFRC)
- Minnesota Sustainable Housing Initiative
- Energy-efficient windows, doors, and skylights resources from U.S. Department of Energy
Adding Windows
Bringing more daylight into a room can be a desirable plan for remodeling projects. It reduces dependency on artificial lighting and contributes to a healthier indoor environment for occupants. Daylighting Studies have been shown that spaces with natural daylight create a more stimulating atmosphere and result in increased occupant production and satisfaction.
Unfortunately, adding or enlarging windows carries some negative impacts as well as no window, even the most efficient triple-pane fiberglass window, insulates as well as a poorly insulated wall. However, the thoughtful addition of a window in the home can be a net energy saver if it is south facing for passive solar gain, highly insulative to prevent winter heat loss and shaded during the summer to prevent unwanted solar gain. Instead, design your remodeling projects to locate the right number and size of windows where they will offer the most benefit. As a general rule of thumb, total window area should not be more than 15 to 18% of floor area, this is called the window to floor ratio. Following this rule will help balance first cost, energy use, and indoor air quality.