SikaShield®, The Global Champion of Bituminous Membranes

Whether you're an architect, roofing applicator, or building owner, selecting the right modified bitumen roofing system for your project can be a challenge. Trying to compare the different properties and characteristics of each product is confusing and every manufacturer says that their product is the best! So how do you know if you are choosing a system that will stand up to the elements and last for decades? Easy, put your trust in Sika, a global leader in roofing and waterproofing with over 100 years of modified bitumen expertise and thousands of performing roofs all over the world!

Modified Bitumen like most roofing and waterproofing solutions can come in a wide range of quality and performance. At Sika, we only produce solutions that perform “beyond the expected” which is why our customers choose SikaShield® branded modified bitumen membrane to protect their investment. SikaShield is not only made from premium raw ingredients but uses them in the right combination to achieve better results in cold flexibility, heat resistance, viscosity, softness, and longevity.

Thanks to its superior waterproofing qualities, SikaShield is widely used in commercial construction, either for new buildings or renovation projects. SikaShield membranes are a thin, reinforced bituminous layer of waterproof material fully bonded to the substrate. It is flexible and able to maintain its waterproof capacity without the risk of cracking.

Installation Flexibility

SikaShield bituminous membranes can be installed with many different application methods to meet the project or applicator's needs (torch, self-adhered, mechanically attached, hot, or cold applied). 

Durability

SikaShield bituminous membranes are highly resistant to mechanical damage, punctures, and foot traffic. It is resistant to hail and other extreme weather events that typically cause membrane tearing. It also has high dimensional stability, important in areas with seasonal climate and temperature changes.

Expertise and Support

Sika offers best-in-class expertise and support, thanks to our worldwide experience and strong know-how in bitumen, waterproofing, and roofing technologies. Our corporate and local technicians are available to help the architectural community and assist our approved applicators on the job.

What is modified bitumen roofing and/or waterproofing?

Modified bitumen (mod. bit.) is a type of roofing or waterproofing membrane that combines asphalt with polymer modifiers to enhance its performance and durability. It is commonly used in commercial and industrial buildings.

What are Modified Bitumen Membranes made from?

Mod. Bit. membranes are made from modified asphalt with a laminated sheet reinforcement in order to provide mechanical properties. The top side of the membrane can incorporate a layer of sand, granules, foil, talc, etc. which may add sustainable “cool roof” features or provide enhanced performance characteristics.

What is the history of Modified Bitumen Membranes?

Modified bitumen membranes have a rich history in roofing and waterproofing applications, evolving from traditional asphalt products to advanced, high-performance materials.

The use of asphalt for roofing dates back to the late 1800s in Europe, primarily using solid bitumen. The introduction of polymers in the 1950's-1960's led to significant advancements.Styrene-Butadiene-Styrene (SBS) and Atactic Polypropylene (APP) became popular as modifiers for bitumen, enhancing flexibility, UV resistance, and overall performance. This period marked the commercial availability of both APP and SBS-modified bitumen products.

In the 1970's-1990's the use of modified bitumen membranes grew rapidly in the United States in locations such as Texas, Florida, the Midwest, and the Northwest due to their enhanced performance characteristics, including improved elasticity, adhesion, resistance to thermal cycling, and durability. They became widely adopted in both low-slope and steep-slope roofing systems as well as below-grade waterproofing applications. Since then, continuous improvements in manufacturing techniques, such as the introduction of advanced polymer blends and innovative installation methods (like cold-applied or self-adhesive systems), have further enhanced the effectiveness of modified bitumen membranes. Today, there's a
strong focus on sustainable practices, including the use of recycled materials in membrane production and reflective surfaces that reduce heat absorption and can clean the air.

What is the difference between SBS and APP mod. bit. membranes?

Both SBS (Styrene-Butadiene-Styrene) and APP (Atactic Polypropylene) modified bitumen membranes are types of waterproofing materials used in construction applications with different types of polymer modifiers added to have the membrane meet certain performance criteria. 

SBS membranes are made from a polymer that adds softness and flexibility to the bitumen which results in superior performance in cold temperatures with excellent adhesion to the substrate. Because SBS is more elastic, it is suitable for environments with significant temperature changes and able to withstand extreme temperature fluctuations. They are also better for applications requiring resistance to cracking. 

APP membranes are made from a polymer that creates a more rigid structure. Atactic polypropylene enhances UV resistance and thermal stability, making it better for hot climates. Because APP is more rigid, it also is more durable and has better impact resistance. This is good for applications where extreme weather, such as hail or heavy foot traffic on the roof is a concern.

Hybrid Membranes are those that use both SBS and APP bitumen layers together to get the benefits of both chemistries. A special kind of polymer called APAO is used to allow the SBS and APP membranes to bond together. Why choose just one type of membrane when you can have a hybrid membrane that has both SBS and APP sheets in one?

What are the key components of a modified bitumen roofing and/or waterproofing system?

The system is composed of several key components that work together to provide effective waterproofing. Here's a breakdown of the typical components:

A primer is typically applied to the roof substrate (such as concrete, wood, etc.) before the membrane installation. The primer enhances the adhesion of the bitumen to the roof surface, ensuring a secure bond. It is also especially important to make the surface clean and free of contaminants.

The base sheet is the first layer of modified bitumen applied to the roof deck. It is usually self-adhering or applied using a torch or cold adhesive. This layer serves as a foundation for additional layers and offers initial waterproofing protection.

The cap sheet is the top layer of the modified bitumen roofing system. It is typically a more durable layer with added protection against UV rays, weathering, and physical damage. The cap sheet is never left exposed and incorporates a layer of sand, granules, foil, talc, etc. which may add sustainable “cool roof” features or provide enhanced performance characteristics. It's also usually self-adhered, torch down, or heat welded.

Modified bitumen membranes are often adhered to the roof surface using heat-welding, cold adhesive, or self-adhesion techniques. Some systems may also use mechanical fasteners (like nails or screws) in conjunction with adhesives to secure the layers to the roof substrate.

A vapor barrier may be installed on the interior side of the roofing assembly to prevent moisture from migrating into the roof structure. This can be particularly important in areas with high humidity or where condensation could occur in the building.

Some modified bitumen systems also include insulation or hardboards as part of the roof assembly. Insulation helps improve energy efficiency, while protection boards protect the roofing membrane from mechanical damage during installation or maintenance.

How is modified bitumen installed on roofs?

Modified Bitumen can be installed using a few different methods:

Torch-down: The bitumen layers are heated with a torch to melt the underside of the membrane, allowing it to bond to the surface.

Self-Adhering: A peel-and-stick membrane that bonds to the surface without heat.

Cold Adhesive: A sticky adhesive is applied to bond the membrane to the substrate.

Mechanically Attached: Using a metal plate and screw, the membrane is secured to the substrate.

How long does modified bitumen roofing last?

Modified bitumen roofing systems typically have a lifespan of 20 to 30 years depending on factors like the quality of the installation, maintenance, climate, and the quality of the product used. The SikaShield HB79 membrane however has been third-party certified by the British Board of Agrement to have a "service life in excess of 35 years."

Are modified bitumen membranes resistant to chemicals and other contaminants?

Modified bitumen membranes are fairly resistant to a range of chemicals and environmental contaminants, but their effectiveness can vary depending on the chemical nature and the specific modification used.

Hydrocarbons: Modified bitumen membranes typically have some resistance to hydrocarbon-based chemicals like oils, fuels, and some solvents, especially when APP-modified.

Acids and Alkalis: The resistance to acidic and alkaline substances is more limited. Strong acids, alkalis, or concentrated chemicals can degrade the membrane over time.

Industrial Contaminants: In industrial environments where exposure to harsh chemicals (such as strong solvents, cleaning agents, or certain industrial by-products) is common, modified bitumen may not offer long-term protection unless specifically formulated for enhanced chemical resistance.

What maintenance is required for modified bitumen roofing?

Modified bitumen roofing, commonly used for flat or low-slope roofs, is durable and long-lasting but still requires periodic maintenance to ensure it performs optimally. Here's a breakdown of the maintenance tasks typically needed for a modified bitumen roof:

Regular Inspections at least twice a year (spring and fall), plus after severe weather events (heavy storms, high winds, etc.).

Clean Gutters and Drains at least twice a year, or more frequently depending on the local environment (e.g., if you're in an area with lots of leaves or debris).

Inspect and Maintain Roof Penetration Flashings such as vents, pipes, HVAC units, skylights, etc. to ensure that all are sealed tightly and have intact flashing around them. These areas are vulnerable to leaks and require extra attention during inspections.

Are there sustainable attributes for modified bitumen systems?

Modified bitumen systems offer several sustainable attributes, such as increased durability, energy efficiency, potential recyclability, and reduced maintenance needs. These factors contribute to their long-term sustainability when considered from a lifecycle perspective.

Extended Service Life: Modified bitumen membranes, such as those reinforced with SBS (styrene-butadiene-styrene) or APP (atactic polypropylene), are generally more durable and resistant to wear, UV degradation, and temperature fluctuations than traditional asphalt-based roofing systems. Longer service life means fewer replacements, reducing material waste and the environmental impact associated with roofing repairs and replacements.

Reflective Coatings: Some modified bitumen systems are available with reflective or cool roofing options, where reflective granules or coatings are applied to the surface. These help reduce the urban heat island effect, lower cooling costs for buildings, and improve energy efficiency by reflecting sunlight away from the building.

Recycled Content: Certain modified bitumen systems incorporate recycled materials, such as rubber from tires or post-consumer plastics, which can reduce the demand for virgin raw materials and decrease overall environmental impacts.

Recycling at End-of-Life: Some modified bitumen membranes are designed to be recyclable at the end of their service life, which helps reduce landfill waste. This is particularly true for systems that use certain polymer additives that can be reused or processed into new materials.

What is "torch down" roofing?

As mentioned above, torch-down roofing refers to a method of application used with Modified Bitumen membranes where a hand-held torch is used to melt the bottom side of the membrane. 

How thick should a modified bitumen roof be?

The thickness of a modified bitumen roofing system generally depends on the product and the specific need of the installation, but typically modified bitumen membranes range from 1.5mm to 5mm thick and always have at least two layers. The thickness of the total membrane layers will determine the durability and resistance to impact damage.

Can Modified Bitumen be used on a flat roof?

Yes, modified bitumen roofing is commonly used on flat roofs and is one of the most popular choices for low-slope or flat roofing systems. As mentioned above, modified bitumen is a type of asphalt roofing material that has been enhanced with additives (usually polymer modifiers like  SBS or APP) to improve its performance. These additives make the material more flexible, durable, and weather-resistant, which is ideal for the challenges that flat roofs face, such as ponding water and thermal expansion.

Are Modified Bitumen Roofing and Bituminous Waterproofing the same thing?

Although both involve bitumen, modified bitumen roofing is a type of roofing system, while bituminous waterproofing is a waterproofing solution. The two are related by the material used (bitumen), but they are designed for different applications.

What are the warranty options for modified bitumen roofing?

When selecting a modified bitumen roofing system, it's essential to carefully read and understand the warranty terms, including what is and isn't covered, the warranty duration, and the conditions that might void the warranty. Working with a reputable contractor and using high-quality materials can help ensure long-lasting performance and minimize the risk of issues during the warranty period.

As mentioned above, modified bitumen roofing systems typically have a lifespan of 20 to 30 years, depending on factors like the quality of the installation, maintenance, climate, and the quality of the product used. The SikaShield HB79 membrane however has been third-party certified by the British Board of Agrement to have a “service life in excess of 35 years.” As such, we can offer up to a 25-year warranty on the system, an industry record.