What Is a System II Asphalt Roof and When Should Builders Use It?

Asphalt roof system II most commonly refers to either Type II oxidized asphalt used in built-up roofing (BUR) systems or a Class 2 impact-resistant shingle. Type II asphalt is a semi-flat, moderately soft grade suitable for low-slope roofs (up to a ¼-in-12-in pitch) and often used in commercial or multifamily applications. Class 2 shingles, by contrast, are a residential roofing product that provides a basic level of impact resistance but less durability than higher-rated Class 3 or Class 4 shingles. Understanding both definitions helps builders specify the correct system based on project type, slope, and performance requirements.

What is Type 2 asphalt?
Type 2 asphalt is an oxidized asphalt blend used in built-up roofing systems, often referred to as hot-mopped roofing. It has a moderate softening point that makes it ideal for semi-flat roofs and moderate temperatures. Builders use Type 2 asphalt as a bitumen binder between roofing felts and surface layers, forming a waterproof, durable membrane.

What are the different types of asphalt roofing?

There are three main types of asphalt roofing: shingle roofing, roll roofing, and built-up roofing (BUR). Shingle roofing is common in residential applications, while BUR systems are used for commercial and low-slope roofs. Asphalt shingles are further categorized into impact resistance classes, while BUR systems are defined by asphalt type (I, II, III, or IV).

What is a Class 2 roof?
A Class 2 roof refers to an asphalt shingle roof that has achieved a Class 2 impact resistance rating under UL 2218 testing. This means the shingle can withstand impacts from 1.25-inch steel balls dropped from 12 feet without cracking. It provides a basic level of protection against hail and debris but is less robust than Class 3 or 4 roofing systems.

What is the difference between Type 2 and Type 3 asphalt?
The main difference is temperature performance. Type 2 asphalt is softer and designed for moderate climates and low-slope applications. Type 3 asphalt has a higher softening point, making it suitable for steeper slopes or hotter climates. Builders in warmer regions like Florida may prefer Type 3 to prevent asphalt flow, but Type 2 remains common for semi-flat commercial projects.

According to the National Institute of Standards and Technology’s,

“oxidized asphalts are graded by softening point and penetration value to match climate and slope requirements, ensuring proper adhesion and durability in built-up roofing systems.”

Understanding Asphalt Roof System II

For builders, the term asphalt roof system II can be confusing because it refers to two distinct roofing contexts: commercial built-up roofing that uses Type II oxidized asphalt, and residential roofing that uses Class 2 impact-rated asphalt shingles. Both are valid interpretations depending on the project’s scope, slope, and environmental conditions.

This guide clarifies both definitions, explains their intended uses, and outlines when each system is the right fit for new construction or re-roofing projects.

The Role of Type II Asphalt in Built-Up Roofing Systems

Type II asphalt is one of four standardized grades defined by ASTM D312 for built-up roofing applications. Each type is distinguished by its softening point and penetration index, which determine how well it performs under specific temperature and slope conditions.

Type II asphalt has a softening point between 185°F and 205°F, making it ideal for low-slope roofs up to ¼ inch per foot. Builders use it as the adhesive layer in multi-ply BUR assemblies, embedding felts and reinforcing mats to create a waterproof barrier. It is commonly paired with gravel or mineral-surfaced capsheets for additional UV protection.

This grade balances workability and stability. It remains flexible enough for smooth installation while providing long-term weather resistance in moderate climates.

Anatomy of a Built-Up Roof Using Type II Asphalt

A typical built-up roofing system includes multiple layers that together form a continuous membrane. These layers usually consist of:

1. Base Sheet: Installed over the roof deck to provide a stable foundation.
   
2. Ply Sheets: Reinforcing layers of roofing felt, each mopped with Type II asphalt.
   
3. Flood Coat: A final layer of asphalt applied to seal the system.
   
4. Surfacing: Embedded gravel or a mineral cap sheet for UV and impact protection.

    

Each ply is bonded with hot asphalt, creating a monolithic waterproof surface. The result is a system known for its durability and redundancy, qualities that make BUR systems a long-standing choice for commercial and multifamily roofs.

When Builders Should Specify Type II Asphalt

Builders typically specify Type II asphalt for:

• Low-slope roofs: Suitable for slopes up to ¼ inch per foot.
  
• Moderate climates: Performs well where high heat flow is not a concern.
  
• Commercial or multifamily projects: Common for buildings where large, semi-flat roof areas are typical.
  
• Cost-sensitive projects: Offers proven performance at a competitive cost compared to single-ply membranes.

   

Type II asphalt is less suitable for steep-slope or high-temperature environments. In those cases, Type III or IV asphalt is better suited to prevent slippage or asphalt flow.

The Evolution of Asphalt Roofing Systems

Built-up roofing dates back more than a century, evolving alongside modern construction materials. Historically, hot asphalt and roofing felt were the dominant approach to waterproofing low-slope structures.

Over time, new materials like modified bitumen and single-ply membranes emerged, but BUR systems remain relevant due to their redundancy and adaptability. Many public and commercial facilities still rely on Type II asphalt-based BUR roofs because they provide multilayer protection and easy repairability.

Class 2 Asphalt Shingle Systems in Residential Construction

In residential roofing, “System II” or “Class 2” usually refers to the impact resistance classification under UL 2218 testing. The test simulates hail impact using steel balls of varying sizes dropped from specific heights onto asphalt shingles.

A Class 2 asphalt shingle can withstand a 1.25-inch steel ball dropped from 12 feet without cracking or exposing the fiberglass mat. Builders often specify Class 2 shingles in regions with moderate hail risk or where code requires a minimum level of impact protection.

Although Class 2 shingles provide baseline performance, Class 3 and Class 4 shingles offer significantly improved resistance and longevity, often becoming the best choice for long-term roofing value.

When to Use Class 2 Asphalt Roof Systems

Builders should consider Class 2 asphalt roof systems in the following cases:

• Moderate weather regions: Where hail and storm frequency are low.
  
• Entry-level housing: Suitable for budget-conscious builds that still require code-compliant performance.
  
• Shorter design lifespans: Appropriate for properties expected to undergo renovations or re-roofing within 15–20 years.

   

In Florida, where impact resistance requirements vary by county, some regions may allow Class 2 shingles if combined with proper underlayment and fastening systems. Always verify with local code authorities before specification.

Comparing Type II Asphalt and Class 2 Roofing Systems

While they share a name, Type II and Class 2 roofing systems serve different market needs.

Builders working across both commercial and residential markets must recognize these distinctions to select the right system for performance, climate, and code compliance.

Performance and Longevity Considerations

Both systems offer reliable protection when properly installed and maintained. Type II BUR systems can last 20–30 years or more, especially when surfaced with gravel or reflective coatings.

Class 2 shingle systems typically last 15–25 years, depending on product quality, climate, and installation method. Builders can extend service life by ensuring proper attic ventilation and underlayment installation, minimizing heat buildup beneath the roof deck.

In high-UV regions like Florida, reflective granules and UV-resistant coatings help reduce thermal aging, a common cause of asphalt degradation.

Code Compliance and Material Standards

Type II asphalt is defined under ASTM D312, while asphalt shingles are covered under ASTM D3462. Builders should always confirm that materials meet these standards and local building code requirements.

In Florida, compliance with the Florida Building Code (FBC) and Miami-Dade Notice of Acceptance (NOA) is essential for roofing systems exposed to severe weather conditions. Manufacturers often provide documentation verifying compliance for permit submissions.

Ensuring all asphalt products meet ASTM and FBC standards reduces risk and simplifies inspection approval.

Common Builder Mistakes When Using Asphalt Roof Systems

Even with familiar materials like asphalt, errors can compromise roof integrity. Common mistakes include:

• Incorrect asphalt temperature: Overheating oxidized asphalt during installation can cause brittleness.
  
• Insufficient venting: Poor attic ventilation accelerates shingle aging and heat buildup.
  
• Mixing asphalt types: Combining incompatible materials can lead to adhesion failure.
  
• Underestimating slope requirements: Using Type II on slopes greater than ¼ inch per foot can cause asphalt flow.

   

Avoiding these pitfalls begins with understanding the specifications and verifying conditions on site before installation.

Builder Tips for Selecting the Right Asphalt Roof System

1. Identify the roof type: Low-slope roofs typically require built-up or modified systems, while steep-slope roofs use shingles.
   
2. Check climate conditions: Choose higher-grade asphalt in hotter regions to prevent slippage.
   
3. Balance performance with budget: Type II asphalt systems offer durability at moderate cost; Class 2 shingles balance affordability with code compliance.
   
4. Verify product ratings: Always review ASTM and UL labels for accurate classification.
   
5. Coordinate with code officials: Confirm slope and impact resistance requirements early in project planning.

    

Builders who follow these steps ensure their roof systems meet both functional and regulatory demands.

When to Upgrade Beyond System II

While System II provides reliable baseline performance, certain projects benefit from higher-grade materials.

• Type III or IV Asphalt: For steeper or high-heat applications.
  
• Class 3 or 4 Shingles: For higher impact resistance in storm-prone regions.
  
• Modified Bitumen Systems: For flexible, torch-applied membranes offering enhanced UV and puncture resistance.

   

Upgrading ensures longer service life and fewer maintenance issues, an investment that often pays off through reduced warranty claims and enhanced customer satisfaction.

Conclusion

An asphalt roof system II can refer to two different roofing approaches: Type II oxidized asphalt for built-up roofs and Class 2 asphalt shingles for residential use. Both serve vital roles in modern construction. Builders must interpret the term based on context, slope, and building type to ensure the correct specification.

Understanding these distinctions allows for smarter material selection, code compliance, and long-term performance. Whether it’s a semi-flat commercial roof bonded with Type II asphalt or a residential roof using Class 2 shingles, builders who choose the right system create durable, cost-effective roofing assemblies that meet project goals.

Key Takeaways:

• Type II asphalt is ideal for low-slope, moderate-climate built-up roofs.
  
• Class 2 shingles offer basic impact resistance for residential applications.
  
• Always confirm slope limits and ASTM standards before specifying.
  
• Proper ventilation, installation, and surfacing extend asphalt roof life.
  
• Upgrading to higher grades enhances durability and client satisfaction.

   

For code-compliant asphalt roofing design and builder consultation, contact CitySide Roofing today.

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