How does reflective attic insulation impact roofing performance?
Reflective insulation has emerged over the years as a versatile option for keeping homeowners’ electricity bills down by making their houses more energy-efficient. It’s become extremely useful in attics during the summer months due to its ability to reflect the sun’s radiant heat back outside instead of letting the attic insulation absorb it and make the entire house warmer.
However, we often get questions about whether reflective attic insulation is detrimental to roof shingles due to its reflective ability. After all, if they’re sending that hot sunlight back outside through the roof, wouldn’t it be going through the roof shingles and deteriorating them?
In this article, we want to answer that question once and for all and provide detailed explanations on how reflective attic insulation works, how they function in accordance with roof shingles, and why they don’t have the deleterious effects on shingles that some may think.
What is reflective attic insulation?
First, it’s important to go over what reflective attic insulation is, how it works, and its various benefits for homeowners.
During the summer, your attic becomes incredibly hot due to the sun’s radiant energy heating the roof shingles. The shingles then transfer that heat through the roof into the attic through conduction. The heat becomes trapped up there and the only direction it can move is down towards the east of the house, causing it to become warmer.
In the winter, the heat that’s generated from your house has the opposite effect. The warmth generated from your heaters travel to the attic, and since science dictates that heat moves from warm areas to cold areas, the heat escapes outside. These processes end up making your summer months hotter and your winters colder, eventually driving up your air conditioning and electricity bills.
Reflective attic insulation addresses this issue by reflecting radiant heat back to its source rather than absorbing it. Highly reflective material reflects the radiant heat from the sun while keeping the heat generated from inside your home from escaping by reflecting it back into the house. Reflective attic insulation generally takes the form of sheets of foil that are placed on the ground or walls of your attic.
This can be extremely beneficial for homeowners during the summer, a time where cranking the AC is nearly unavoidable. By reducing radiant heat from entering through the attic, your home becomes much more energy-efficient, therefore reducing your electricity bill. This energy efficiency carries over to the winter months, as reflective attic insulation transfers heat back down and keeps your house warmer.
All of this might sound great on paper, and perhaps some readers may already be familiar with how reflective attic insulation works. It’s important, then, to address whether reflective attic insulation has actually been effective in practice.
Want more information on reflective attic insulation? Read our full article on what is and how it works here.
How effective is reflective attic insulation?
There have been numerous studies conducted to test whether reflective insulation works as intended, and the extent to which they can reduce heat transfer into homes. Through these studies, scientists have that reflective insulation is relatively effective at reducing heat flow and making homes cooler
A 2013 study observed percentage reductions in heat flow – or the movement of heat from the sun towards a surface – of 25% to 42% in ceilings that used reflective insulation. Furthermore, a 2019 study found that reflective insulation reduces indoor summer heat gains by as little as 10% and as much as 53% while reducing indoor summer surface temperatures by as much as 30 degrees Fahrenheit. They also discovered that reflective insulation reduces heat gains during the daytime while dissipating heat through the house at night, resulting in better indoor cooling throughout the entire day.
These statistics show that reflective insulation, especially when applied to the heat-trapping nature of most attics, can be effective in reducing overall heat during hotter months. But this doesn’t completely address the question of how roofs and roof shingles are affected by the reflective process. After all, won’t the heat that’s being reflected back to the sun heat up the roof as well?
How reflective attic insulation impacts roofs
Unlike traditional insulation materials such as fiberglass or foam, reflective attic insulation does not hold radiant heat once it comes in contact with it. It reflects about 90% to 97% of the heat back to the roofing materials, at which point the roof emits most of that heat back into the air almost immediately.
All of this may sound oversimplified, so investigating the details of how reflective attic insulation manages to do this is warranted, as is debunking various myths about roofing performance once you’ve installed reflective insulation.
Will it overheat my roof shingles?
As we stated, reflective attic insulation does not substantially increase roof temperature, even during the hottest months of the year. Roofs with reflective insulation installed in the attic will only see minor temperature increases, generally between 2 to 10 degrees Fahrenheit. Most asphalt roof shingles are designed to handle incredibly high temperatures, well above the maximum temperatures that most houses actually experience in any given year.
It’s important to note that roof temperatures are determined by two factors: the color of the shingles and the ventilation of the surfaces beneath it. As for color, dark-colored shingles can increase roof temperatures significantly, often generating about 20 degrees more heat than light-colored roofs. Ventilation is a key component of roof temperatures as well since air temperature and wind movement can have a cooling effect on rooftops. Roofs absorb heat from the sun, but airflow can also cool roofs and help bring down overall temperature.
As such, black asphalt roof shingles absorb over 90% of the heat that strikes them, allowing them to easily heat up to over 170 degrees on a hot day. But taken into context, a homeowner with reflective attic insulation will not substantially increase their roof temperatures, as that heat that is being radiated through the roof shingles are immediately being reflected back outside.
So if you’re wondering whether reflective insulation is going to melt your roof shingles, take comfort in knowing that won’t be the case. If anything, the color of your asphalt shingles is a greater determinant of your roof temperature.
Where does the reflected heat go?
While it’s certainly true that installing reflective insulation under a roof will cause that roof to heat up, this accounts for about 2 to 10 degrees of actual heat increase. The heat that would usually be absorbed by your attic’s insulation is instead being bounced back to the roof deck. This causes the roof to emit more heat upward back to the source, rather than emitting it both upward and downward and heating up your attic in the process.
The roof is essentially gaining heat, then immediately losing it by having reflective insulation underneath the shingles. Think of it as having a single light bulb in a room. The bulb sends out light and heat throughout the entire room, illuminating everything around it. Say you add a reflector to the bulb. Now the light and the associated heat are being redirected downward. The amount of light and heat has not changed – only the direction in which it’s emitting.
This is essentially what happens with roofs with reflective attic insulation installed. The amount of heat on a roof hasn’t changed by a whole lot, but instead of radiating that heat in every direction – as in upwards toward the sky and down into the attic – it’s mostly being radiated upward and away from your home.
How does reflective attic insulation help my roof?
Like we mentioned earlier, studies have shown that reflective insulation allows homes to be more energy efficient by dissipating heat throughout the house at night. Traditional insulation material can absorb heat during the night, and dissipate it all around the house and even outwards onto the roof itself.
Reflective attic insulation blocks much of the heat from reaching mass insulation, thereby preventing your house from warming up and your air conditioning turning on in the middle of the night. This process inadvertently extends the life cycle of your roof shingles, since radiant heat isn’t being emitted out onto the roof by mass insulation during the night.
So is reflective attic insulation good for my roof?
This answer may vary depending on where you live, how much sunlight you receive during the summer and a few other factors. However, reflective attic insulation is generally positive for most homeowners, as it not only provides greater energy efficiency during hot summer months, it can improve the durability of your roof shingles.
If your home is covered by shade throughout most of the year, you won’t be able to enjoy all of the benefits that come with reflective attic insulation due to the lack of sunlight that your roof will be exposed to. But if your roof is constantly exposed to sunlight, reflective insulation will help your home remain cool while reducing wear and tear on the roof shingles themselves.
As such, reflective attic insulation should not void your shingle manufacturer’s warranties, but factors such as attic ventilation and water vapor transmission should be considered when evaluating the state of your shingles.