Sun streaming through glass can heat a room faster than the air conditioner can respond. This guide covers the main ways to cut that heat, and why exterior and interior shades are not equal.
Sunlight passes through glass as shortwave radiation and is absorbed by floors, furniture and walls, which then warm the room. The heat that arrives this way is called solar heat gain, and it is a big part of why sunny rooms are uncomfortable in warm weather. Window orientation matters: windows facing the sun at low angles, often to the east or west in the northern hemisphere, can be especially hard to manage.
The glass itself has a rating called the solar heat gain coefficient. A lower figure means the glass lets in less solar heat. Replacing windows is costly, so many households start with shades, screens and habits instead.
The angle of the sun changes through the year, which is why a window that is fine in winter can overheat in summer. A fixed overhang can shade a high summer sun while letting in the lower winter sun, and adjustable options such as retractable shades give a similar flexibility without construction.
Building-science sources generally find that exterior shading is more effective than interior shading at limiting solar heat gain. The reason is simple. A shade outside the glass stops the sun before it reaches the window, while an interior shade stops it after the sun has already come through and been converted into heat in the space between the glass and the shade.
One widely cited building-science article puts interior drapery over clear glass at roughly a fifth to three-fifths of solar gain blocked, depending on material and color, and credits awnings with blocking a larger share on south-facing windows. Take the ranges as rough guidance, since fit, color and the window itself change the outcome.
Exterior options include awnings, solar screens and roll-down screens. See exterior patio and retractable shades for those. Interior shades are easier to install and are still useful, as covered next.
Light-colored, reflective-backed shades and tightly woven solar fabrics reduce the heat that reaches the room. A lower openness fabric blocks more, as explained in the openness guide. Cellular shades add a trapped air layer that helps both in summer and winter, covered in the cellular shade guide.
Fit matters. A shade with large gaps at the sides lets heat flow around it, and a shade that sits tight to the glass can trap warm air against the window. An outside mount that overlaps the opening usually covers more. Learn how to size it in the measuring guide.
A reflective or light-colored face on the window side of the shade helps send some sun back through the glass, while a dark face absorbs more heat. Check the specification for the shade fabric you are considering, and ask the maker how it is tested. Be cautious of claims that sound too large to be true.
Shades only help if they are down when the sun is on the glass. People forget, and that is where automation pays off. A motorized shade on a schedule can drop on the west side in the afternoon and rise at night. See motorized and smart shades.
Without automation, build a routine. Close shades on sun-facing windows in the morning on hot days, open them at night to let cooler air in if conditions allow, and keep blinds angled to bounce light toward the ceiling rather than down onto the floor.
Do not forget skylights and glass doors. They often admit more sun per square foot than regular windows, and ordinary shades may not be made for those shapes. Ask about products designed for skylights and large patio doors, and measure with extra care.
Window film, awnings, trees and exterior louvers all affect heat gain. Film is a surface treatment applied to the glass, and results depend on the product and the window. Ratings from independent bodies such as the National Fenestration Rating Council can help compare products. Check the manufacturer's guidance before applying film to double-pane or special glass, because some glass can be damaged.
Landscaping can also help. A deciduous tree on the sun side shades in summer and lets light through in winter. Local rules and the lifespan of trees affect this choice, so treat it as a longer plan.
If a room still runs hot after the sun is blocked, the cause may be elsewhere, such as an attic, a poorly insulated wall or an overloaded cooling system. Shades solve the window problem, but a professional energy assessment can look at the rest of the home.
Start with the windows that get the most sun. For each one, decide whether an exterior solution is possible, then add an interior layer for glare and privacy. If you can only do one thing, pick the sun-facing window that makes the room uncomfortable.
Tell us about your windows through the consultation form and we can talk through the options. Be wary of any seller who promises a specific temperature drop or a dollar saving without knowing your windows.
First, identify which windows face the sun in the hottest hours. Second, shade those from outside if you can. Third, add interior shades with a tight fit and a light face. Fourth, automate or build a habit of closing them in time.
Finally, keep notes. If the room is still too hot, try a different fabric or a better fit before concluding that shades do not work. Small changes in timing and fit often matter more than the product itself.
Generally yes, because they stop the sun before it reaches the glass. Interior shades still help and are simpler to install.
They help by blocking sun at the window, but heat that passes through the glass first can warm the space behind the shade. Fit and color matter.
It can reduce solar heat gain, depending on the film and the glass. Check ratings and compatibility with your window before applying.
Start with the windows that get the strongest direct sun in the hottest part of the day.
Tell us which kind of shade you are considering and we will reply about measuring and options.