Reflection & Ventilation
A Two Step Strategy for Cooling Your Home
A house that gets uncomfortably hot or humid can make warmer
summer temperatures more difficult to enjoy.
The good news is there are a number of strategies you can use to keep
your home cool, which don’t rely on energy-consuming air conditioners and
fans. Reflection and ventilation are two
basic concepts that – when properly applied – can be highly effective methods
for cooling your home.
Step 1 – Reflect Heat
Away from the Exterior:
When it comes to cooling your home, it’s helpful to work from the outside in,
and focus first on reflecting away the sun’s warming rays. Home exteriors can absorb up to 90 percent of
the radiant energy from the sun, so it is important to mitigate this issue
where- and when-ever possible.
About a third of the unwanted heat that builds up
in your home comes in through the roof. Traditional roofing materials such as
asphalt and fiberglass can absorb up to 70% of solar radiation, which is then
transferred into your home by way of conduction.
One way to address this issue is to apply a
reflective coating to your existing roof. There are two types of coatings available
at your local hardware store or lumber yard – one is a white latex coating and
the other is asphalt based and, contains glass fibers and aluminum particles. Both
types have waterproof and reflective properties and are marketed primarily for
mobile homes and recreational vehicles.
Another way to reflect heat off your roof is to
install a radiant barrier on the underside.
A radiant barrier is simply a sheet of aluminum foil with a paper
backing. When installed correctly, this type of barrier can reduce heat gains
through your ceiling by up to 25 percent.
Wall color is not as important as roof color, but
it does affect heat gain somewhat. White exterior walls absorb less heat than
dark walls. And light, bright walls increase the longevity of siding,
particularly on the east, west, and south sides of the house.
Roughly 40 percent of the unwanted heat that
builds up in your home comes in through windows. Reflective window coatings are
one way to reflect heat away from your home. These coatings are plastic sheets
treated with dyes or thin layers of metal. Besides keeping your house cooler,
these coatings also cut glare and reduce fading of furniture, draperies, and
Two main types of coatings include sun-control
films and combination films. Sun-control films are best for warmer climates
because they can reflect as much as 80 percent of the incoming sunlight. Many
of these films are tinted, however, and tend to reduce light transmission as
much as they reduce heat, thereby darkening the room. Combination films allow
some light into a room but they also let some heat in and prevent interior heat
from escaping. These films are best for climates that have both hot and cold
Note: Do not place reflective coatings on
south-facing windows if you want to take advantage of heat gain during the
Step 2 – Remove Built
Up Heat on the Interior
Reflecting heat away from the home is only one piece of the puzzle, however,
one of the most important things you can do to cool down your home is to force
existing warm air out and encourage cool air to enter.
This strategy only works, however, when the inside temperature is higher
than the outside temperature, so the key is to only ventilate during the
coolest parts of the day or night, and seal off your house from the hot sun and
air during the hottest parts of the day. The climate you live in will determine
the best ventilation times.
with cool nights and very hot days: let the night air in to cool your
house. A well-insulated house will gain only 1° F (0.6° C) per hour if the
outside temperature is 85° to 90° F (29° to 32° C). By the time the interior
heats up, the outside air should be cooler and can be allowed indoors.
climates with daytime breezes, open windows on the side the breeze is
coming from and on the opposite side of the house. Keep interior doors open to
encourage whole-house ventilation. If your location lacks consistent breezes,
create them by opening windows at the lowest and highest points in your house.
This natural "thermosiphoning," or "chimney," effect can be
taken a step further by adding a clerestory or a vented skylight.
hot, humid climates where temperature swings between day and night are small,ventilate when humidity is not excessive. Ventilating
your attic greatly reduces the amount of accumulated heat, which eventually
works its way into the main part of your house. Ventilated attics are about 30°
F (16° C) cooler than unventilated attics. Properly sized and placed louvers
and roof vents help prevent moisture buildup and overheating in your attic.