Windows & Doors

Windows and doors are the openings through which most energy flows in and out of your building. Use them to provide free heating, cooling, and lighting, and to make your building more pleasant and productive.

1 Shading
2 Daylighting
3 Windows
3 Air leakage

Goal: Save energy through passive design

"Passive design" saves energy without expensive and high–maintenance mechanical systems by planning out the natural heat flow through your building openings in advance (also see heating & cooling). It starts with considering the exterior orientation and landscaping around each window and door, then the sizes and material choices for each opening, and works its way down to caulking gaps around the frames. It all adds up to big savings and a better indoor environment.

area one

Provide shading on east, west and south windows with overhangs, awnings, or deciduous trees

What is this?

Shading windows with overhangs, awnings, or trees keeps heat from coming in through windows while still allowing diffuse daylight in and views out. Overhangs can be optimized to allow in warm direct sunshine during winter and provide shade in summer.

Why do it?

Direct sunshine coming in the window adds to air conditioning needs on hot days — shading windows is the simplest and most cost–effective way to reduce your air conditioning bills.

How to do this?

Size overhangs or awnings to cut off a 30–degree angle from the base of south–facing windows, and use overhangs with vertical fins on east and west facades. Awnings can be retrofitted to existing buildings with overheating problems. Deciduous trees in front of the building can block summer sun and allow in winter sun when they lose their leaves.

Who does this?

Architects.


area one

Plan windows and skylights, light shelves, and window treatments to provide daylight that improves indoor environments

What is this?

Consideration of how daylight reaches indoor spaces and work surfaces is important to making daylighting work inside a building. Light shelves are horizontal dividers between lower "vision" windows and upper daylighting windows that reflect light deeper into indoor spaces; window treatments include louvers, interior and exterior blinds, shades, and tints.

Why do it?

Daylit spaces are naturally comfortable if appropriately designed, and can easily achieve enough light to remove the need for most daytime electric lighting. This can save a large amount of energy, and also make more pleasant spaces that help occupants be healthier and more productive.

How to do this?

Windows and skylights admit light, but controlling the light is very important — glare is a common problem in spaces with too many windows. Various rules of thumb used by architects apply to light shelves and daylighting penetration. For the biggest energy savings or for complex spaces, do daylight modeling in the design process, either with a large–size physical model or various software packages.

Who does this?

Architects, specialized daylighting consultants.


area one

Choose window sizes, frame materials, and glass coatings to optimize energy performance

What is this?

Windows are less well insulated than solid walls, allowing more heat loss in winter and heat gain in summer. Bigger windows lose more heat, and let in more useful daylight and heat through sunlight. Window frames can be an area of high heat loss, and window coatings can help glass to retain heat inside or reflect heat outside as necessary.

Why do it?

Optimizing your windows to meet your expected heating, cooling, and lighting needs can reduce your energy bills substantially.

How to do this?

Building energy simulations — done on a computer — are the best way to realistically forecast the overall energy impact of windows on a design. Use information from National Fenestration Rating Council stickers to judge window insulation and performance levels.

Who does this?

Architects, energy consultants.


area one

Stop air leakage at doors and windows

What is this?

Air leakage, or "infiltration" in building terms, is a major source of unwanted heat gain in summer and heat loss in winter. Window and door frames or openings are the most common major locations of air leakage.

Why do it?

Air infiltration control is one of the most cost–effective ways to improve any building and save money. An investment of less than $50 can save a 2,500 square–foot home around $25 per year; commercial and industrial spaces can also realize rapid returns on this investment.

How to do this?

Use foam or expandable caulk to seal cracks in framing around openings. Use weather–stripping and gaskets on the window and door openings themselves, especially in older buildings.

Who does this?

Building owners, architects, specification writers, contractors, tenants.


More Information

More information on upgrading windows in an existing home