Window Tips: Keeping Homes Cool in the Hottest Climates

How an architect in Mississippi strives to reach the perfect balance between capturing light, leveraging beautiful views, and heat management.

The windows in our homes can fill our favorite spaces with fresh air, warm sunlight, and a calming connection to the outdoors. But if you live in a climate that stays warm year-round, poorly placed and inefficient windows can heat up your home and tax your air conditioner beyond its capacity. According to the National Centers for Environmental Information, Mississippi is the 6th hottest and 4th most humid state in the U.S. So, when Leah Watters, owner of Watters Architecture in Pass Christian, Miss., designs a home, she pays careful attention to how fenestration can help mitigate the southern heat, humidity, and penetrating effects of the sun. Here she shares helpful tips on how to keep a home comfortable, reduce energy costs, and be a good steward of the environment.

Choose the Right Glass

U-Factor is a rating system used to measure how well a window prevents heat from escaping your home. The lower the U-Factor number, the better the window is at retaining heat. This is an important consideration in cold climates, but in regions where it stays relatively warm year-round, it’s all about preventing solar heat gain. When sunlight shines through a window, radiant heat will cause the room to get hotter. Solar Heat Gain Coefficient (SHGC) is the rating system that measures how much radiant heat enters the home. The lower the SHGC number, the less heat a window allows inside.

SHGC can be lowered considerably by coating the glass with extremely thin, metallic particles. Glass coated in this way is called low emissivity (Low E) glass. Low E glass typically has one layer, while Low E2 has two, and yes you guessed it, Low E3 has three low emissivity layers. The effectiveness of today’s coatings is far superior to the coatings 40 years ago when the technology hit the housing market. And in addition to reducing solar heat gain, Low E glass also protects rugs, carpet, furniture, artwork, and other expensive items from the harmful effects of the sun’s UV rays.

Leah explains what a game changer Low E glass has been, “Traditionally, here in the south, the heat of the western sun has been somewhat of an enemy and has limited us from creating large expanses of glass. But that challenge has been mitigated by the high performance of today’s windows. Marvin Low E3 windows are our standard and we’ll step it up to Low E4 if a client wants a westerly facing sunroom.”

Manage Air Movement

In addition to lowering solar heat gain, it’s important to think about how the air flows through a home. Here are some helpful tips that will let you take advantage of those rare but welcome cool breezes.

• Try to direct the breeze across the areas where people are spending the most time.
• Air flow will increase if the outlet window is larger than the inlet window vs. the other way around.
• Cross ventilation is best. Windows placed in the exact position on opposite sides of the room will leave much of the room unventilated.
• Install at least two windows per room, even in rooms that have only one exterior wall.
• An awning window placed higher on a wall can allow heat to escape a room faster.
• A strategically placed casement window can scoop up a breeze and direct it indoors.

Some Like it Shut

In the most humid areas of the country, like lower Mississippi, some windows may rarely get opened at all. Many homeowners keep their homes buttoned up and enjoy their fresh air time in a screened porch. Leah says, “Here in this part of the south, many of my clients just don’t open the windows a whole lot because the amount of days when the air is dry and cool enough isn’t all that many. So if the homeowner does not anticipate opening a particular window, and egress doesn’t matter, we’ll save money, and improve views by installing stationary windows with no screens.”

Made in the Shade

When it comes to battling the sun, don’t make your windows do all the work — take advantage of the shade when you can. Interior shades can be a cost effective way to both cool and enhance the interior styling of a room. And because they are easy to operate, especially with today’s smart home options, people are more likely to use them on a regular basis. But truth be told, while interior shades will definitely keep a room cooler, when the sun hits the back of the shades, they will heat up, and that heat will be introduced into the room. It’s better to block direct sunlight from ever reaching the glass in the first place. “We built this house with generous overhangs,” Leah says. “Not only to help shed water far away from the building, but also to shade many of the windows from the noonday sun.” Here are some more tips for thwarting the sun.

• Overhangs, porches, and pergolas provide shade and create popular outdoor living spaces.
• Well planned tree cover can not only supply shade but can actually cool the air temperature by as much as 10 degrees.
• Awnings work well but are not always an option stylistically.
• Louvered shutters can provide protection while keeping the air flowing.

Fiberglass is an Ideal Option

Windows made from fiberglass are uniquely suited to withstand extreme heat and blistering sun. Unlike vinyl, fiberglass does not lose structural integrity in the heat nor does it expand and contract near as much. In fact, the expansion and contraction rate is similar to glass, which means seal failures and stress cracks are not a worry. “Marvin is the only window we choose at this point because of the fiberglass line,” Leah says. “The Elevate collection hits the perfect price sweet spot and allows us to provide a beautiful wood interior and durable fiberglass exterior, perfect for our harsh coastal climate. Also, our clients are looking for more functionality, durability, and building materials that don’t require a lot of maintenance. And with black windows being so popular, black vinyl just doesn’t hold up as well.”

Living Well

Of course, mitigating soggy air, scorching temps, and the brutal rays of the sun will always play a role in choosing window, style, size, and placement in the south, but homeowners always want to take advantage of beautiful views and cozy sunlit places where they can relax and rejuvenate. And thanks to Marvin’s high-performing windows, home designers like Leah can put her clients’ desires first. “While we will always try to build our homes sun-smart and energy efficient, the first questions for our clients are always, ‘Where do you spend the most time and feel most alive in your home.’ If someone doesn’t like to see the sun in the morning, we may not design the main bedroom into the east side of the house. The places most important to them will get the sweet spot when it comes to views. It’s always so rewarding when we design a house and get feedback from the clients that they live well in it. They live efficiently. All the spaces are being used.”

Photos courtesy of Watters Architecture