Dreading Those Summer Electric Bills?
At the very center of how well your home handles the summer heat is its roof system and attic. We would like to discuss energy efficiency in detail, and explain the things to consider when trying to minimize your home air conditioning costs.
Of course, it goes beyond just cost savings. We’re committed to ecologically sound operations and products. One of the ways we do that is by supplying products and recommending systems that reduce energy consumption.
How can your home’s roof system and attic save energy?
The first thing to respect is just how vulnerable your roof is to the sun. While we often do things to insulate the walls of our homes, the roof is actually far more prone to the sun’s radiant heat than the walls are. The roof is often forgotten as a place to stop unwanted heat from entering your home.
But, if heat does get through your home’s roof, you actually have a second chance that lies within the performance of your home’s attic. You can use insulation to stop heat transfer through your attic into the living space and you can also often vent the heat back outside where it belongs.
Let’s start at the top …
For many years, homeowners in hot climates have used white or light colored roofs for their reflective nature. These roofs help to reflect radiant heat and reduce heat transfer into the attic. That is an option for all homeowners but, in response to the fact that many homeowners do not want a light colored roof (plus, with most products, they gather dirt and lose their light color over time), the metal roofing industry has started to use reflective pigments in its paint systems. These reflective pigments help to reflect radiant heat even in dark colors. It is these pigments that have led to the US DOE Energy Star rating for many metal roofs. So, a light colored roof or a metal roof with reflective pigment in the coating will provide the best “first line of defense” against the sun’s heat.
Next, let’s look at thermal mass …
Any roofing material sitting in the sun will gather heat and become warm to the touch. For maximum energy efficiency, you want a roof that quickly sheds that heat as soon as the sun goes behind a cloud or even when a gentle breeze blows. Products that have great thermal mass, though, such as standard composition shingles and tile, gather and hold that heat, continuing to radiate it into the home even hours after the sun has gone down. Aluminum roofing and steel roofing both dissipate heat quickly (think of that piece of aluminum foil and how quickly it cools down once you remove it form your oven). So, ideally, you want a roof that quickly sheds any gained heat.
What’s a thermal break?
Heat is transferred pretty efficiently by conduction. This means that one material gets warm sitting in the sun and anything that material touches also gains heat through conduction. One of the best ways to stop conductive heat transfer is with a dead airspace. That is known as a thermal break. It is the same concept that happens with double pane windows – the very tiny air space between the two panes of glass is adequate to stop heat transfer. So, while a metal roof may get warm to the touch, if we can minimize contact between the metal and your home, that is a good thing. This is done in a couple of ways with today’s metal roofs. First, metal roofs that are formed to look like shake, shingle, slate, or tile have an integral airspace between the metal and the roof deck, creating a natural thermal break. And, in the case of flat metal roofs that sit right on the roof deck, they can often be installed on battens to create the thermal break between the metal and the roof deck.
Venting out the heat that does get through …
It’s inevitable that some heat from the roof top will get through the roof system. In most residential construction, ventilation is the way to get that heat back to the outside. Ventilation is achieved by bringing fresh air in at the bottom of the roof and exhausting it out at or near the peak of the roof. As this air travels through the attic, it bathes the under side of the roof deck with fresh air, carrying both heat and also any moisture that has migrated into the attic away from the home’s living space. Metal roofs are designed to easily accommodate exhaust vents and there are also some options to help increase intake vents if a home has limited intake venting.
Finally, insulation on the floor of your home’s attic serves as a final line of defense to help keep summer heat gain from entering the living space. This insulation is also perfectly located to help hold heat inside the living space during the winter.
What about the winter?
A roof and attic system that performs well in the summer will also perform well in the winter. During the winter, there are two goals. One is to hold heat inside the home. This is done with insulation on the floor of the attic. The second goal is to vent out any heat and moisture that do enter the attic. This is done with ventilation. Good insulation and ventilation will also serve the purpose of helping avoid ice dams on the roof in the winter which result when heat from inside the home reaches the snow on the roof.
Special circumstances: conditioned attics
Increasingly, homes are constructed with conditioned attics. In these cases, the entire interior surface of the attic is sprayed with closed cell urethane insulation which serves both as a vapor barrier to reduce moisture migration into the attic and as a high R-Value insulation. This results in an attic that is not vented but instead is well insulated to prevent heat gain in the summer and heat loss in the winter. The downside is that insulating the underside of the roof deck can cause roofing materials such as asphalt shingles to age prematurely. That is not the case with metal though. Metal makes a great covering for fully insulated attics.
Need more help?
We hope this information makes sense and can help you to a roofing decision that will lower your summer energy costs, and give you extra savings for more fun and enjoyment in your life. If you would like more information, please let us know.