Whether the time has come to replace your roof, or you’re considering buying a new home, metal roofs are something you need to know about. If you’re already looking into metal roofs, black metal roofs may be raising some concerns for you.
Black roofs are popular because a lot of people like the appearance of a black roof better than a white or uncolored metal roof. Regular or white metal roofs can create a lot of glare when the sun is shining, and some people feel that it takes away from the aesthetic of the house.
But we all know that black reflects less light than other colors, and that leads to a common question: will a black metal roof make my house hotter?
Will a Black Metal Roof Make My House Hotter?
The short answer is: not if it’s installed properly.
The long answer is that metal roofs in general, and even black metal roofs, are unlikely to heat up your home. This is a bit counter intuitive, since we all know that metal conducts heat very efficiently compared with other roofing materials, but it makes sense when you start to think about the differences between a metal roof and other roofs.
It may surprise you to learn that metal roofs are much, much lighter than roofs made with other materials. Roofs are often measured by the square, which is an area of 100 square feet.
Metal roofs weight 50-150 pounds per square, while typical roof tiles weigh about 750 pounds per square, and concrete tiles weigh 900 pounds per square. So, metal roofs are the lightest roofs you can get.
To understand why weight matters, you need to understand thermal mass. Thermal mass is a description of an objects ability to retain heat, and it’s directly related to the objects mass (it’s weight and it’s density). Thermal mass is what makes cast iron such a popular material for cookware. Cast iron heats very unevenly, which would normally be a problem, but because cast iron cookware has to be made thick and heavy to avoid breaking, it retains heat better than almost any other material.
Cast iron pans heat up more slowly than aluminum pans, but they also cool down more slowly. So, aluminum pans are more responsive to changes in heat. The same is true for any material. If you chill a five gallon jug of water down to forty degrees, you can leave it out at room temperature for hours, and possibly even a day or two before it gets warm. An 8oz glass of water would heat up much faster.
A metal roof has a lot less thermal mass than a typical roof. So, it heats up a lot faster in the sun, but it also loses heat faster. A typical asphalt roof, by contrast, will heat up more slowly during the stay, but it will stay hot for a long time afterward, radiating that heat into the house. It’s possible that a typical shingle roof will get hotter and stay hotter than a metal roof.
Metal reflects light, and sunlight is what heats up the roof. So, the more reflective a roof is, the less it’s going to heat up in direct sunlight. The vast majority of roof shingles in the United States are asphalt shingles, and anyone who’s stepped barefoot onto the street on a summer day can tell you that asphalt gets hot when it’s out in the sun all day.
That’s because, in addition to it’s high thermal mass, asphalt is not a very reflective material. It absorbs a lot of the sunlight that hits it, which causes it to heat up. In hot climates the asphalt can get hot enough to melt the soles of your shoes and damage tires.
Metal reflects more light than any other roofing material. Even a black metal roof will reflect more light than ceramic, concrete, or asphalt tiles. That will make a big difference in the amount of heat that a black metal roof absorbs, and it minimizes the chance that it will make your house hotter.
Proper Installation Is Important
A black metal roof may heat up faster than a shingle roof, and it may lose heat faster, but that won’t matter very much if the roof is not built correctly. Proper construction and installation of a roof, no matter what material it is, will prevent the roof from affecting the internal temperature. If you are curious about the longevity of your metal roof, check out our blog about how often to replace your roof.
Insulation is the first and most obvious way to prevent your roof from heating up your house. Properly installed insulation between your roof and your attic will prevent heat transfer from the roof to the rest of the home. This is one of the first things you should check on when you’re looking into replacing your roof. If the insulation is insufficient, it won’t matter what roofing material you choose, your house will be too hot or too cold.
After insulation, the next most important thing is proper roof ventilation. There should be constant airflow through the attic, allowing hot air to escape to prevent a buildup of heat and moisture inside the attic.
When the roof is properly ventilated, it becomes even more difficult for the roof to heat up your house. Even if your insulation is installed perfectly, there’s going to be some heat transfer. With good airflow, that heat gets whisked away by the movement of the air through the attic before it can make your house hotter.
With good insulation and proper roof ventilation, your roof should have minimal, if any, effect on the temperature inside your home. That’s true whether you have a black metal roof or a white ceramic tile roof.
Black Metal Roofs Don’t Heat Up Your House
If you walk outside on a hot day, climb up and touch your black metal roof, it’s probably going to be hot to the touch. It might even burn your hand. But that heat isn’t going inside your house. What’s more, your neighbor’s asphalt shingle roof probably isn’t much cooler, and it’s going to stay hot a lot longer.
Roof materials just don’t have as much effect on the temperature inside our homes as we intuitively think they do, as long as the roof is installed correctly. The biggest factors in maintaining a comfortable temperature inside the house will always be insulation and ventilation.
The same is true for keeping your house warm in the winter, by the way. Some people in cooler climates are interested in black metal roofs because they think it will help them heat up their house more quickly, but that just won’t work.
And if you’re thinking that maybe you could install a black metal roof without insulation, to facilitate heat transfer into the house, remember that heat transfer works both ways. If it’s colder outside the house than it is inside, then a metal roof with no insulation will just be radiating the heat from inside into the air outside, making your house colder, not hotter.
There are lots of very good reasons to install a black metal roof. Metal roofs are very tough and durable, so they’ll last a long time. When installed properly, they’re nearly impervious to leaks. They usually stand up to hail very well, and high winds won’t damage them the way they will with shingle roofs. Plus, because they weigh less and they’re quicker to install, they’re often cheaper than shingle roofs. You don’t need to worry about a black metal roof making your house hotter. As long as the roof is well ventilated and the insulation is installed right, there’s little to no difference between a metal roof and a shingle roof when it comes to the temperature of your home. It won’t make your house any hotter.s