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Why Do Shingles Have Granules On Them? In-Depth Explanation


why do shingles have granules?

I am in the process of installing radiant barrier foil in my attic and was on the roof getting surface temps for a before and after study. My feet knocked some granules loose and when they fell to the ground my son asked why these granules are on the roofing shingles.

That got me to researching and I learned a lot. If you have wondered about this as well, I have the answer. And it’s a bit more complex that you may realize.

Why do roofing shingles have granules? Granules were first added to shingles in the early 1900s and were primarily used for durability. Ceramic granules came along several decades later and offered numerous color options not previously available. Years later, the source material for the granules was modified with a focus on also reducing susceptibility to ultraviolet light as well as inhibiting organic algae growth.

I found this information in multiple places, most notably in this historical information from the U.S. Forestry Service.

Purpose Of Granules On Asphalt Shingles

Roofing granules serve several purposes:

  • Installation – helps to prevent the asphalt shingles from sticking together and provides an improved walking surface for installers.
  • Durability – granules help to ensure a lasting performance of shingles as they are exposed to harsh weather conditions over the years.
  • UV Protection – The sun’s harsh ultraviolet rays would quickly deteriorate asphalt shingles if not for these granules.
  • Aesthetics – With a variety of color options available, granules add an aesthetic value to the look and quality of roofing shingles.

Granules are a critical ingredient to asphalt shingles and their ability to withstand the harsh weather conditions that they endure year after year, not only from the sun but from rain, hail, and snow throughout the winter.

What’s really crazy is the technology and thought that goes into making these granules. It’s more than just grinding down some stone into small pieces. Much more!

You have heard of 3M, right? That’s the company that makes Post-It notes. Well, they also are a leading manufacturer for those granules on your shingles.

3M acquired a company named Wausau Abrasives back in 1929. With their entrance into the asphalt granule marketplace, the company put its reputation for ingenuity to work and in 1970 was granted a patent for a special algae-resistant granule.

Their system for these algae-resistant granules later earned the Scotchguard brand and in 2006, the company began marketing 3M Cool Roofing Granules (source).

3M actually produces four different types of these roofing granules.

  • 3M Classic is a natural mineral coated in ceramic with a coloring pigment embedded in it.
  • 3M Copper Granules provide resistance to algae growth and the black streaks that form on shingles from this growth.
  • 3M Smog-Reducing Granules are specially designed to be environmentally friendly by converting nitrogen oxide into more eco-friendly water-soluble ions.
  • 3M Cool Granules offer solar reflectivity which, in theory at least, result in higher energy efficiency. These granules have a highly reflective coating that comes in a variety of colors and can contribute to a shingles Energy Star certification qualification.

You can read more about these technologies on the 3M website.

So while those little granules may seem to be just pieces of rock, there’s a lot that has gone into making sure that they are effective. Who knew?

As stated earlier, granules on asphalt shingles also add to the aesthetic appeal. Roofing choices these days are based as much on aesthetics as they are on performance, which isn’t exactly ideal.

The Department of Energy has long advocated for the concept of “cool roofs”. This energy efficiency strategy involves the use of lighter color roofing materials to increase reflectivity and reduce heat absorption (source). Yet in many parts of the country, darker roof coloring is considered more aesthetically appealing.

Energy Star rates roofing materials based on their energy efficiency and grants Energy Star certification when strict criteria is met (source). One example of an Energy Star Certified roofing shingle is Owens Corning Duration Premium Cool product line. These shingles reportedly include granules that reflect solar energy, thereby reducing the heat transfer to the attic.


As it turns out, there is a lot of information worth knowing about those asphalt shingles on your roof. I’ve compiled some of the most common questions below.

Is It Normal For Granules To Come Off Of Shingles?

The answers to this vary based on the situation and severity. Let’s explore each.

Newly Installed Shingle Granule Loss

New roof shedding granules – It is normal for a new roof to have some level of granule loss. This is due in part to the installation process where handling and walking on the shingles dislodges granules from the asphalt. If you are noticing granules in your gutters on the ground around your house following a new roof installation, you should expect that to subside within a few weeks.

Normal Degradation and Granule Loss

Some level of granule loss is normal and the result of daily exposure to UV rays and weather. A minimal, consistent level of granule loss will occur with asphalt shingles. When you should be concerned is when you are noticing a large amount of granule loss in a specific area of the roof.

Old Roof Shingle Granule Loss

There can be multiple causes for this. Age and deterioration of the shingles, results of high winds or rainfall, or cumulative effects of both. The condition of your shingles should be inspected, especially if you are noticing significant granule loss in certain areas of the roof versus a uniform loss more likely associated with normal aging (source).


What Are Asphalt Shingles Made of?

According to the Asphalt Roofing Manufacturer’s Association, roofing shingles are comprised of felt, asphalt, and granules. They are designed to protect the roof and provide resistance to water, hail, ice, and high winds. Manufacturer’s offer products with varying degrees of performance against these natural elements.

You may hear asphalt shingles referred to as fiberglass shingles. This is because the felt consists of a fiberglass mat within the asphalt which adds strength (source).

How Many Square Feet Does A Bundle Of Shingles Cover?

Generally, a bundle of shingles will cover just over 33 square feet. Singles are often sold in sets of three bundles, for around 100 square feet of roofing coverage.

The average size for asphalt roofing shingles is about 39 inches wide and 13 inches deep but this can vary greatly depending on the brand, type, and style of shingle selected.

How Long Are Roofing Shingles Warranted?

Roofing shingles are generally warranted for 20-25 years. Low cost “economy” shingles can be purchased with shorter warranties but as a result of that low cost, they are often manufactured with lower quality materials.

Because of the critical role that roofing shingles play in protecting your home, quality shingles from a manufacturer with a strong reputation for quality is recommended. There are a lot of ways to save money but installing low-quality roofing shingles is not one of them.

If your home does not have shingles that utilize cool home technology, learn what you need to do to reduce heat transfer into your home. There are two essentials routes that you can take:

Click here to learn pros and cons of Foam Insulation.

You can also read about installing a radiant barrier in your attic to reduce the transfer of heat from your roof in an upcoming post. Stay tuned!

Paul

As a homeowner, I am constantly experimenting with making the structure of my house more energy-efficient, eliminating pests, and taking on DIY home improvement projects. Over the past two decades, my family has rehabbed houses and contracted new home builds and I've learned a lot along the way. I share my hard-learned lessons so that you can save time and money by not repeating my mistakes.

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