Understanding how to properly install radiant barrier insulation in relation to your local climate is simple if you understand how heat is traveling within your home.
In the south or southern climates with mild winters, radiant barriers are installed in the top of the attic or along the roof joists. In the scorching summer months, radiant heat hits the roof of a building and is absorbed into the home. The daily temperature is already uncomfortable to most peoples preference. This daily temperature is the starting point for an attics base temperature.
Radiant heat travels into the attic while the attic temperature climbs. The fiberglass insulation, although good in winter months, warms and holds this elevated temperature into the night. Attic temperatures can easily average 120 degrees in summer months in any climate. All the while you want the inside of your home around 70 degrees.
Adding a radiant barrier to the roof joists creates a break or barrier to stop this absorption of radiant heat. The attic is now not allowed to heat up as high as once before. This lowers the temperature difference between your attic and your living space.
Heat loss for homes in these warm regions is generally not much of a concern. Therefore, the thought of warm air escaping from the living space into the attic is not dealt with.
In northern or cold climate regions however, the major concern is stopping heat loss from escaping out of the living space. In these homes, radiant barrier insulation should be installed on the attic floor, laid over the existing fiberglass insulation. As heated air from a home radiates into the colder attic, a barrier is created that holds back this radiant heat and does not allow it to escape.
Now, what happens if you want to control both summer heat gain and winter heat loss in a home?
If you have been paying attention you will know the answer is do both. Install radiant barriers in both the roof joists, and across the attic floor. This effectively seals off the attic, allowing radiant heat to be neither gained nor lost.
Always make sure to use a perforated product in attic applications to allow the necessary moisture transmission.