What Is Modified Bitumen Roofing?

Giovanni Valle is a licensed architect and LEED-accredited professional and is certified by the National Council of Architectural Registration Boards (NCARB). He is the author and managing editor of various digital publications, including BuilderSpace, Your Own Architect, and Interiors Place.

Many people are using modified bitumen roofing for their homes, especially those who have slow-slope and flat roofs. This roofing material is considered to be one of the most reliable and popular because it is versatile, affordable, low maintenance, and long-lasting. But what is modified bitumen?

Bitumen is a sticky, waterproof material used commonly for roofing. Modified bitumen roofing uses polymer-modified bitumen reinforced by several layers of glass fiber or polyester fabric or a combination of the two. Modified bitumen roofing can be installed conventionally or can be self-adhered.

However, before you opt for modified bitumen roofing for your own home, you need to know what it is exactly made of and what makes it a versatile roofing material. You also need to make sure it is the right roofing solution for you, and how you can install it. Read on to know more about modified bitumen roofing.

What Is Bitumen Made Of?

Bitumen is a viscous, sticky, and waterproof substance that is a key component in asphalt. It is commonly used in construction, particularly for paving and roofing. Bitumen is considered one of the most high-demand construction materials globally, with more than 100 billion tonnes used every year.

Bitumen as Roofing Material

Proof of bitumen being used to bond the walls of water tanks can be traced back to around 3,000 B.C. Since then, it has become a leading roofing component, with 10 percent of the world’s overall bitumen production going to the making of roofs.

Because of its waterproofing capabilities, bitumen is perfectly suited for a range of roofing systems, such as single-ply membrane systems, felt roofing, and asphalt roofing.

A bitumen roof is also durable. The high-tensile strength of bitumen makes the roof unlikely to develop cracks. This type of roof is also rated to stand against wind, hail, and fire. It is unlikely to get damaged in case of a storm. Bitumen roofs usually come with a long manufacturer’s warranty, which guarantees its longevity. Bitumen roofs can last 20 years or more.

Regardless of how bitumen roofing is applied, whether as self-adhesive sheets, as cold-applied adhesives, or as hot-mopped asphalt, its seams are typically melted together. This seamless method helps stop leaks, unlike in other types of membrane roofing wherein the seams are covered with another material or are left open and eventually weaken.

What Is Modified Bitumen?

Over the years, advancements in technology have paved the way for innovations in roofing systems. Modified bitumen is one example of these innovative roofing products, where other materials are added to the bitumen to make it longer-lasting and even more durable. Modified bitumen is a common material for membrane roofs, which are typically used in commercial roof construction.

Engineered modified bitumen roofing originated in Europe in 1965, and the material has been used in the U.S. and Canada since 1975. This roofing system is designed to withstand exposure to extreme environmental elements. It features five layers of protection and is now one of the most trusted flat roofing systems in the building industry.

The modified bitumen roofing system’s framework consists of a five-layer combination of roofing components. These components are:

Insulation. This is used to provide thermal resistance and contribute to a roof system’s temperature stability.
Modified-bitumen membranes. These factory-made sheet membranes are composed of copolymer that is reinforced with fiberglass or polyester.
Modified-base sheets or plies. These lightly modified fiberglass base sheets are coated with modified bitumen asphalt.
Adhesive. This is a waterproofing material combined with a bonding agent and is applied hot or cold.
Surfacing. This provides the roof with its weather-resistance capability and protects it from the sun’s ultraviolet rays.

Types of Modified Bitumen Roofing

These are the two types of modified bitumen roofing systems:

Atactic Polypropylene Bitumen or APP

This type of modified bitumen roofing uses thermoplastic polymer, which gives the asphalt its plastic-like quality. As a result, APP modified bitumen gives your roof better protection from U.V. light exposure and allows it to better resist water.

When installers torch-apply APP, the plastic starts to melt at 148.89°C (300°F). It melts into an almost free-flowing liquid wax-like substance that you can mop across a surface of the roof. When heated, APP has a high-temperature tolerance, so it is easier for installers to apply.

The ease of melting APP makes this type of modified bitumen popular on smaller roofs like those of residential properties and the flat roofs of commercial buildings.

Styrene-Butadiene Styrene or SBS

Styrene-butadiene styrene is added to bitumen to give it a synthetic rubber modification. SBS does not melt the way APP does, but instead, it offers a sticky kind of melt that increases as it gets hotter. In other words, SBS lacks the liquid flow that APP has, and this means that it takes less heat to install it. As such, SBS-bitumen roofing is faster to install than APP.

SBS roofing systems can also be installed using a cold adhesive, which makes it more preferable for construction projects that do not permit open flames.

Moreover, SBS-bitumen is more flexible than the plastic used in the APP, thanks to the rubber that is used in its construction. The flexibility of SBS means that it has recovery properties that allow it to withstand the elements, like wind, as well as the temperature fluctuation, expansion, and contraction.

And when it comes to installation time, SBS-bitumen takes faster to install because it is not affected by aging or oxidization.

Which Type of Modified Bitumen Roofing Should You Use?

Deciding on the type of modified bitumen to use for your roofing depends on your project. If you want to lower the time you spend on installation or if you want to avoid using open flames, SBS-modified bitumen is the better option. It will give you the versatility you need while also providing the same degree of hardwearing weather-proofing.

Meanwhile, APP-modified bitumen is more forgiving when you install it under hot-melt conditions, so it may be preferable if torching is allowed. APP is also the better choice if you want better flow characteristics when you install the roofing.

Why Use Modified Bitumen Roofing?

Modified bitumen roofing has a proven track record in terms of performance. It is a practical choice because it has superior waterproofing characteristics, and it is a low-maintenance roofing system. It can last for a long time with just the most basic care and maintenance. Plus, due to its polymer modification, this roofing system can withstand both low and high temperatures.

This roofing system is also versatile, with a broad range of application or installation methods. Moreover, you can apply additional sheets or layers of polymer to boost its durability. This makes roof repairs easier, too.

Another good reason for using modified bitumen roofing systems is that they come with long-term warranties.

Disadvantages of Using Modified Bitumen Roofing

When you go for a modified bitumen roofing system, it also helps to know of its drawbacks.

For one, bitumen roofs have a black color, so they can absorb heat instead of reflecting it. And while the material does not get damaged by U.V. rays or by heat, the absorption of heat can lead to superheating in the building if insulation is not applied properly.

Another disadvantage is that if your roof is prone to gather puddles or hold a lot of standing water after rainstorms, this can damage or prematurely age your bitumen roof.

Final Thoughts

Modified bitumen roofing is a good roofing system for your home because it is durable, long-lasting, easy to install, low-maintenance, and resistant to water and U.V. rays. These are pretty much everything you would want for your roof, which is the part of your house that gets the most exposure to harsh environmental elements. And with roofers typically giving you long-term warranties for this kind of roofing system is assurance enough.