It's probably not a surprise that a metal roofing company will regularly be asked whether a metal roof is hot, or if it makes the home underneath hotter. We've addressed this before, but since it's our goal to provide useful information about metal roofing, it's worth repeating.
Hot or Not?
There are two considerations to answer a question about metal roof and heat. The first involves the roof covering material (in this case, metal roofing) and second is the construction of the roof assembly.
When it comes to the heat absorbency of metal, there are a few variables.
- Color & Finish - Both will affect heat absorbancy. Metal exposed directly to the sun will most certainly heat up, but whether or not it heats up more or less than other roofing materials is directly related to the color and finish. Many of our metal roof products have Energy Star finishes that are certified to be reflective of sunlight, which makes them cooler than older finishes. And, as one would assume, a lighter color will absorb less heat than a dark color.
- Roof Absorbency - It's true that a metal roof will absorb heat when directly exposed to the sun. But so will a roof covering of any material. A dark roof in asphalt, ceramic, slate or any other material will absorb heat at about the same rate, and in fact, the same color in differing roofing materials is unlikely to result in a roof-top temperature difference of any significance.
- Weight & Density - Once the sun stops shining directly on a roof, it's the lightest weight material that will cool the quickest. The lightest roof available? You might have guessed. It's is metal, which means it cools the fastest. Once the sun is no longer shining on a metal roof, it reverts to the same temperature as the surrounding air. Heavier materials like slate or concrete mean a heavier mass, which means longer heat retention. The longer these roofs stay hot, the more heat transferred to the building beneath. In terms of roofing materials contributing to heat in a building, metal is the best possible option once the sun is no longer shining.
The Role of Attic Space
Now that we're clear on the role of roof color and material on the amount of collected heat, let's move on to the bigger contributor of heat conduction into a house. And that's the type of construction between the roof and the home below.
If a room beneath the roof has an attic, then controlling the temperature of the attic with a "cool" roof like metal is important. Even more important is properly ventilating that attic to ensure it stays within a few degrees of ambient air temperature. By properly ventilating the attic, you're giving the insulation in the ceiling the best possible scenario for keeping the room from gaining heat from the ceiling. Ceiling insulation is also an important consideration. The more insulation - and the higher its quality - the less heat from the attic will be conducted into the rooms below. That's important in the warm summer months. In the winter, the opposite is true - less heat being conducted the other way.
A Simple Test
bUse it to take the temperature of the ceiling, floors and walls in various rooms, and you'll be able to see which surfaces are contributing the most heat.
More questions? Fire away! You can call us directly at 775-737-9169 or check our Resources page for our re-roofing booklet and comparison sheets.