When you’re looking at roofs, especially for commercial buildings, you’ll hear a lot about built-up roofing, or BUR. It’s been around for ages, and for good reason. Basically, it’s a system made of layers, kind of like a really tough sandwich for your building. We’re going to break down what makes up these roofs, how they get put together, and why they’re still a popular choice for keeping things dry and protected.
Key Takeaways
- Built-up roofing (BUR) is a multi-layer system using asphalt and reinforcing materials like felt.
- The structure involves preparing the roof deck, applying layers of felt and asphalt, and a final protective surfacing.
- Asphalt acts as the binder, while various felts and surfacing options like gravel or cap sheets provide durability and weather resistance.
- BUR systems are known for their longevity and reliability, especially on low-slope commercial buildings, offering good resistance to foot traffic.
- While durable, BUR can be heavy and labor-intensive to install, and may become brittle in very cold temperatures.
Understanding Built-Up Roofing Systems
Built-Up Roofing (BUR) systems have been a staple in low-slope and flat roofing for decades, especially in commercial and industrial buildings. Think of it as a layered approach to keeping water out. It’s not just one sheet of material; it’s a robust assembly designed for durability.
Core Components of Built-Up Roofing
At its heart, a BUR system is made up of several key elements that work together. You’ve got the roof deck, which is the structural base. Then comes the insulation, if it’s part of the design, followed by multiple layers of reinforcing materials and asphalt. The whole thing is topped off with a protective surfacing.
- Roof Deck: The structural foundation, usually wood or metal.
- Insulation (Optional): Provides thermal resistance.
- Waterproofing Layers: Alternating layers of asphalt and reinforcing felt.
- Surfacing: Typically gravel, mineral granules, or a cap sheet.
The Role of Multiple Layers in BUR
Why so many layers? It’s all about redundancy and creating a really tough barrier. Each layer of asphalt acts as an adhesive and a waterproofing agent, while the reinforcing felts (often made of asphalt-saturated materials) add tensile strength and stability. This multi-ply construction means that even if one layer experiences a minor issue, the others are there to keep water out. It’s a system built for reliability.
Distinguishing BUR from Other Low-Slope Systems
BUR stands apart from other low-slope options like single-ply membranes (TPO, EPDM, PVC) or modified bitumen. While single-ply systems are typically large, continuous sheets, BUR is built up on-site, layer by layer. Modified bitumen is similar in its asphaltic nature but uses factory-manufactured rolls with polymer modifiers for added flexibility. BUR is known for its traditional, robust construction method.
BUR systems are characterized by their layered application of asphalt and reinforcing materials, creating a durable and time-tested waterproofing solution for low-slope roofs.
Structural Layers of Built-Up Roofing
A built-up roofing (BUR) system is a layered assembly, designed for low-slope or flat roofs. It’s not just one thing; it’s a combination of materials working together to keep water out. Think of it like a really robust sandwich, but for your roof.
Roof Deck Preparation for BUR
Before anything else goes on, the roof deck needs to be in good shape. This is the base layer, usually made of wood or metal, that everything else attaches to. It needs to be clean, dry, and structurally sound. Any old roofing material, debris, or moisture needs to be cleared away. If there are any weak spots or damage, they have to be fixed first. Sometimes, a vapor barrier is installed at this stage, especially in areas with significant temperature differences, to stop moisture from getting into the roof assembly from inside the building.
Application of Reinforcing Felts
This is where the "built-up" part really starts. Reinforcing felts, often made of asphalt-saturated felt or fiberglass, are laid down. These felts are the backbone of the membrane. They’re typically applied in overlapping layers, with hot asphalt or another adhesive used to bond each layer to the one below and to the deck. This creates a continuous, strong membrane. The number of felt layers can vary depending on the desired performance and the specific system design. More layers generally mean a more robust and waterproof roof.
The Function of Asphalt Inter-Layers
Between each layer of reinforcing felt, a hot asphalt inter-layer is applied. This asphalt acts as the primary waterproofing agent and the adhesive that binds the layers together. It fills any small gaps and creates a monolithic surface. The asphalt needs to be applied at the correct temperature and thickness to ensure proper adhesion and prevent brittleness or flow. This continuous asphaltic layer is what makes the BUR system so effective at preventing water from finding its way through.
Here’s a look at the typical layers in a BUR system:
| Layer Name |
|---|
| Roof Deck |
| Vapor Barrier (Opt.) |
| Primer (Opt.) |
| Reinforcing Felt #1 |
| Asphalt Inter-Layer |
| Reinforcing Felt #2 |
| Asphalt Inter-Layer |
| … (additional layers) … |
| Reinforcing Felt #N |
| Asphalt Inter-Layer |
| Surfacing (Gravel/Cap Sheet) |
The integrity of the entire built-up roofing system hinges on the proper installation and adhesion of each individual layer. Any compromise in one layer can affect the performance of the whole assembly.
Materials Utilized in Built-Up Roofing
Built-up roofing (BUR) systems are constructed using a combination of materials that work together to create a durable, waterproof membrane. The effectiveness of a BUR system relies heavily on the quality and proper application of each component.
Asphalt as a Binding Agent
Asphalt is the backbone of most BUR systems, acting as the primary waterproofing agent and adhesive. It’s a petroleum-based product that, when heated, becomes a viscous liquid capable of binding layers together. There are two main types used:
- Asphalt (Bitumen): This is the standard material, typically applied hot. It’s cost-effective and has a long history of use in roofing.
- Coal Tar Pitch: While less common now due to environmental concerns and odor, coal tar pitch was historically used, especially in applications requiring excellent waterproofing and resistance to ponding water.
The viscosity and application temperature of the asphalt are critical for proper adhesion and performance. Too hot, and it can damage the felt; too cool, and it won’t spread evenly or bond effectively.
Types of Reinforcing Felts
Reinforcing felts are the structural component of the BUR system, providing tensile strength and stability. These are typically installed in multiple layers, saturated and coated with asphalt.
- Asphalt-Saturated Felt: This is the most traditional type, made from organic or fiberglass materials that are saturated with asphalt. It provides a good base for the asphalt layers.
- Asphalt-Coated Felt: Similar to saturated felt, but with an additional coating of asphalt on the surface, offering enhanced water resistance.
- Fiberglass Felt: Lighter and more dimensionally stable than organic felt, fiberglass felts offer good tear resistance and are less prone to shrinking or expanding with temperature changes.
These felts are laid in overlapping courses, with hot asphalt applied between each layer to create a monolithic, waterproof membrane. The number of felt layers can vary depending on the desired thickness and performance of the roof system.
Aggregate and Cap Sheet Surfacing Options
The final layer, or surfacing, of a BUR system serves multiple purposes: protecting the underlying asphalt from UV radiation and physical damage, providing fire resistance, and offering aesthetic options.
- Gravel Surfacing: This is a very common finish. Small, uniformly graded gravel is embedded in a flood coat of hot asphalt. It’s effective at protecting the membrane from sunlight and foot traffic, and it helps with fire resistance. The gravel needs to be clean and dry for proper adhesion.
- Cap Sheet: A prefabricated roofing sheet, often made of asphalt-coated fiberglass or polyester mat, surfaced with mineral granules. Cap sheets are typically applied over the base layers using hot asphalt, cold adhesive, or self-adhering methods. They offer a more finished look and can provide enhanced UV protection and durability compared to just gravel.
- Coated Surfaces: Some BUR systems are finished with specialized reflective coatings instead of gravel or cap sheets. These coatings can significantly reduce surface temperature, contributing to energy efficiency.
Each surfacing option has its own set of benefits and considerations regarding cost, installation, maintenance, and performance characteristics.
Installation Process for Built-Up Roofing
Putting together a built-up roofing (BUR) system is a methodical process that requires careful attention to detail at each stage. It’s not just about slapping down layers; it’s about creating a cohesive, waterproof barrier that can stand up to the elements for years. Think of it like building a really sturdy cake, but instead of frosting and sprinkles, you’ve got asphalt and felt.
Deck and Insulation Preparation
Before any roofing materials even touch the building, the foundation needs to be just right. This starts with the roof deck itself. It needs to be clean, dry, and structurally sound. Any old roofing material, debris, or loose fasteners have to go. If there are any low spots or uneven areas, they get fixed up to create a smooth surface. This is super important because any imperfections underneath can eventually show up in the finished roof, or worse, cause problems down the line. If insulation is part of the system, it’s installed at this stage too. This usually involves rigid insulation boards that are either mechanically fastened or adhered to the deck. Making sure the insulation is laid flat and securely attached is key for its performance and for the integrity of the whole roof.
Layering Felts and Asphalt
This is where the ‘built-up’ part really comes into play. The process involves applying multiple layers, alternating between reinforcing felts and hot asphalt. The felts, often made of fiberglass or asphalt-saturated organic material, act as the reinforcement for the system. They’re rolled out and embedded into a flood coat of hot asphalt. Each subsequent layer of felt is laid in the opposite direction of the one below it, and each is thoroughly coated with asphalt. This cross-layering technique adds strength and helps prevent the roof from cracking or developing weaknesses. The number of felt layers can vary depending on the desired performance and thickness of the final roof system, but typically, you’ll see at least three.
Applying the Final Surfacing
Once all the reinforcing felt layers are in place and sealed with asphalt, it’s time for the final protective layer. This is what gives the roof its finished look and provides the primary defense against UV rays and physical wear. The most common surfacing is gravel or crushed stone, which is embedded into a final hot asphalt flood coat. This not only protects the asphalt below from the sun but also adds weight, which helps hold the roof down. Another option is a cap sheet, which is a specially designed asphaltic membrane that can be applied with hot asphalt, cold adhesive, or even self-adhered. Cap sheets often come with granules embedded in them, similar to asphalt shingles, and can offer a more finished appearance. Sometimes, reflective coatings are applied over the surfacing to help reduce heat absorption, making the building more energy-efficient.
Performance Characteristics of Built-Up Roofing
Durability and Longevity of BUR
Built-up roofing (BUR) systems are known for their toughness. They’re made of multiple layers, which means if one part gets a little nick, the whole roof doesn’t immediately fail. This redundancy is a big plus. Think of it like having several layers of protection instead of just one. This layered approach, often using asphalt and reinforcing felts, creates a really robust barrier against the elements. Properly installed and maintained, a BUR system can last a long time, often 20 to 30 years or even more. It’s a tried-and-true method that has been around for ages for a reason.
Resistance to Foot Traffic
One of the standout features of BUR is how well it handles foot traffic. This is especially important for commercial buildings where maintenance crews or HVAC technicians might need to access the roof regularly. The multiple layers, particularly when topped with a layer of gravel or a tough cap sheet, provide a surface that can withstand the wear and tear of people walking on it without easily puncturing or damaging the underlying waterproof layers. This makes it a practical choice for roofs that see regular activity.
Weatherproofing Capabilities
BUR systems are excellent at keeping water out. The way the layers are applied, with asphalt acting as a waterproof adhesive between each felt layer, creates a seamless membrane once it’s all installed. This continuous surface, especially when finished with a protective top layer like aggregate or a cap sheet, offers great protection against rain, snow, and even standing water. The materials used are designed to resist UV degradation and temperature fluctuations, helping to maintain their integrity over many years and through various weather conditions.
Advantages of Built-Up Roofing Systems
Proven Track Record in Commercial Roofing
Built-up roofing, often called BUR, has been around for a really long time, like over a century. It’s been used on tons of commercial buildings, from warehouses to office complexes. This long history means it’s a system that’s been tested by time and weather across all sorts of conditions. When you see a BUR roof, you’re looking at a system that has a solid reputation for doing its job, year after year. It’s not some newfangled material that might have unknown issues down the road; it’s a tried-and-true method that builders and building owners have relied on for ages.
Redundancy and Reliability
One of the coolest things about BUR is how it’s built. It’s not just one single layer; it’s multiple layers of asphalt and reinforcing felt, kind of like a sandwich. This layered approach means that even if one layer gets a small nick or tear, there are other layers underneath to keep the water out. This redundancy is a big deal for reliability. It’s like having a backup plan built right into the roof itself. This makes it a really dependable choice, especially for flat or low-slope roofs where water can sit for a while if drainage isn’t perfect. The multiple plies offer a significant safety net against leaks.
Cost-Effectiveness Over Time
While the initial cost of a built-up roof might seem a bit high compared to some other options, especially when you factor in the labor involved, it really shines when you look at its long-term value. These roofs are known for their durability and can last for decades, often 20 to 30 years or even more with proper maintenance. When you spread that cost out over the lifespan of the roof, it becomes a very economical choice. Plus, their resistance to foot traffic and general wear and tear means fewer repair costs over the years. So, while it might not be the cheapest upfront, it’s often one of the most cost-effective solutions in the long run for commercial properties.
Limitations of Built-Up Roofing
While built-up roofing (BUR) systems have a long history and offer many benefits, they aren’t without their drawbacks. It’s important to be aware of these limitations before deciding if BUR is the right choice for your project.
Weight Considerations for BUR
One of the most significant limitations of built-up roofing is its substantial weight. Because BUR systems involve multiple layers of asphalt and reinforcing materials, topped with aggregate like gravel, they can add considerable load to a building’s structure. This means that older buildings or those not originally designed to support such a heavy roof might require structural reinforcements. This can add unexpected costs and complexity to the project. For structures where weight is a primary concern, lighter roofing options might be more suitable.
Labor Intensity of Installation
Installing a BUR system is a labor-intensive process. It requires multiple passes to apply the layers of asphalt and felt, and this work is often done in hot conditions. The application process itself demands skilled labor to ensure each layer is properly adhered and sealed. Compared to some modern single-ply systems that can be installed more quickly, BUR installation can take longer, potentially increasing labor costs and project timelines. This is especially true when dealing with complex roof geometries or numerous penetrations.
Potential for Brittleness in Extreme Temperatures
Asphalt, the primary binder in BUR systems, can become brittle when exposed to very low temperatures. This brittleness can make the roofing membrane more susceptible to cracking, especially if there are significant temperature fluctuations or if the roof experiences foot traffic or impact during cold weather. While modern formulations have improved, this remains a consideration, particularly in climates with harsh winters. Proper installation and maintenance are key to mitigating this risk, but it’s a characteristic inherent to the materials used.
Maintenance and Repair of Built-Up Roofs
Routine Inspection Protocols
Keeping a close eye on your built-up roofing (BUR) system is key to making it last. Think of it like regular check-ups for your car; you wouldn’t wait for a breakdown to get it serviced, right? For BUR systems, this means scheduling inspections at least twice a year, ideally in the spring and fall. You should also do a quick look-over after any major weather events, like heavy storms or high winds. These inspections aren’t just about spotting obvious problems; they’re about catching small issues before they turn into big, expensive headaches. Look for things like pooling water, which can indicate drainage problems, or any signs of wear and tear on the surface, especially around edges and penetrations.
- Spring Inspection: Check for damage from winter weather, like ice dams or freeze-thaw cycles.
- Fall Inspection: Prepare the roof for winter by clearing debris and checking seals.
- Post-Storm Inspection: Assess for any damage caused by high winds, hail, or falling branches.
Addressing Membrane Damage
When you find damage to the BUR membrane, it’s important to act fast. Small punctures or tears can quickly let water in, leading to more serious issues like deck rot or insulation damage. The repair process usually involves cleaning the damaged area thoroughly, then applying a compatible patching material. For asphalt-based BUR, this might mean using a hot asphalt patch or a specialized cold-applied sealant. The key is to ensure the patch overlaps the damaged area sufficiently and creates a watertight seal. If the damage is widespread or affects multiple layers, a more extensive repair or even a partial replacement might be necessary.
The integrity of the entire roofing system relies on the continuous performance of its individual layers. Even minor breaches in the membrane can compromise the underlying structure if not addressed promptly.
Repairing Surfacing Issues
The final surfacing of a BUR system, often gravel or mineral granules, plays a vital role in protecting the asphalt layers from UV radiation and physical wear. If this surfacing is compromised, such as through significant granule loss or displacement, the asphalt beneath can begin to degrade. Repairing these issues typically involves cleaning the affected area and then reapplying a compatible surfacing material. For gravel surfaces, this means adding new gravel and ensuring it’s properly embedded. For cap sheets, any tears or punctures need to be sealed, and if the sheet itself is failing, it may need to be replaced. Keeping the surfacing intact is a straightforward but critical part of maintaining your BUR roof’s longevity.
Built-Up Roofing in Commercial Applications
Suitability for Low-Slope Structures
Built-up roofing (BUR) systems have been a go-to for commercial buildings for a long time, especially those with low-slope or flat roofs. Think of big box stores, warehouses, and office buildings – many of them have relied on BUR for decades. Its layered structure is really good at handling the kind of water pooling that can happen on flatter surfaces. Unlike steep-slope roofs that shed water quickly, low-slope roofs need a system that can create a solid, continuous waterproof barrier. BUR does this by building up multiple layers of asphalt and reinforcing felt, topped off with a protective surfacing. This makes it a reliable choice for keeping large commercial spaces dry.
Integration with Building Codes
When you’re putting a roof on a commercial building, it’s not just about keeping the rain out; it’s also about meeting strict building codes. BUR systems have a long history of compliance, which makes them a familiar and often preferred option for architects and contractors. Codes typically specify requirements for fire resistance, wind uplift resistance, and overall structural integrity. Because BUR has been around for so long, there’s a lot of data and experience showing how it performs under various conditions, making it easier to get approvals and pass inspections. It’s a system that’s proven itself in terms of meeting these important regulatory standards.
Comparison with Single-Ply Membranes
In the world of commercial roofing, BUR often gets compared to single-ply membranes like TPO, EPDM, and PVC. Single-ply membranes are newer, often lighter, and can be installed more quickly. They’re made from large sheets of material, which means fewer seams compared to the layered approach of BUR. However, BUR has some advantages that keep it in the running. Its multiple layers offer a kind of redundancy – if one layer gets damaged, the others can still provide protection. Plus, BUR is known for being really tough and resistant to foot traffic, which is a big deal on commercial roofs where maintenance crews or HVAC technicians might be walking around. While single-ply might be faster to install, BUR offers a different kind of durability and a proven track record that many building owners still value.
Here’s a quick look at how they stack up:
| Feature | Built-Up Roofing (BUR) | Single-Ply Membranes (TPO, EPDM, PVC) |
|---|---|---|
| Installation | Labor-intensive, multiple layers applied on-site | Faster, large sheets, often factory-welded seams |
| Weight | Heavier due to multiple layers and aggregate surfacing | Lighter |
| Durability | Excellent resistance to foot traffic and punctures | Good, but can be more susceptible to punctures |
| Redundancy | High, due to multiple overlapping layers | Lower, relies on the integrity of a single layer |
| Cost | Moderate to high upfront, cost-effective long-term | Variable, can be higher upfront but faster install |
| Typical Use | Low-slope commercial, industrial buildings | Low-slope commercial, industrial, some residential |
Energy Efficiency and Built-Up Roofing
Reflective Surfacing Options
Built-up roofing (BUR) systems, while known for their durability, haven’t always been top-of-mind for energy efficiency. Traditionally, the gravel surfacing common on BUR roofs absorbs a lot of solar heat, which can contribute to higher building cooling costs. However, modern approaches offer ways to combat this. One of the most effective methods is the use of reflective surfacing materials. Instead of standard dark gravel, lighter-colored aggregates or specialized reflective coatings can be applied. These surfaces bounce a significant portion of the sun’s rays back into the atmosphere, rather than absorbing them as heat. This reduction in heat absorption can lead to a noticeable decrease in the roof’s surface temperature, which in turn helps keep the building cooler.
The goal is to reduce the amount of heat transferred into the building, thereby lowering the demand on air conditioning systems. This not only saves money on energy bills but also contributes to a more comfortable interior environment. The effectiveness of reflective surfacing is often measured by its Solar Reflectance Index (SRI), with higher SRI values indicating better reflectivity and lower heat gain. Choosing a BUR system with a high-SRI surfacing is a smart move for any building owner looking to improve their building’s energy performance.
Impact of Insulation Beneath BUR
While the surfacing plays a role, the insulation installed beneath the built-up roofing layers is equally, if not more, important for energy efficiency. The BUR membrane itself offers some thermal resistance, but it’s the dedicated insulation layer that truly makes a difference. Rigid insulation boards, often made from materials like polyisocyanurate (polyiso), expanded polystyrene (EPS), or extruded polystyrene (XPS), are typically installed directly over the roof deck or sometimes over a vapor barrier. These materials have high R-values, meaning they are very effective at resisting heat flow.
Properly installed insulation acts as a thermal break, significantly reducing heat transfer between the interior and exterior of the building. In colder months, it helps keep heat inside, reducing heating costs. In warmer months, it prevents outside heat from penetrating the building, lessening the load on cooling systems. The thickness and type of insulation are key factors in determining the overall thermal performance of the roofing system. Building codes often specify minimum R-values based on climate zone, and exceeding these minimums can lead to even greater energy savings.
Thermal Performance Considerations
When evaluating the thermal performance of a built-up roofing system, several factors come into play beyond just the surfacing and insulation. The overall assembly, including the roof deck, vapor retarders, and the BUR membrane itself, contributes to the system’s ability to manage heat and moisture. A well-designed system will prevent unwanted heat gain in the summer and heat loss in the winter. It also plays a critical role in managing moisture within the roof assembly. Condensation can form if warm, moist interior air comes into contact with cold surfaces within the roof structure, leading to mold, rot, and reduced insulation effectiveness.
Here’s a breakdown of key considerations:
- Vapor Retarders: These are installed to control the movement of moisture vapor from the conditioned interior space into the roof assembly. Their placement is critical and depends on the climate and insulation strategy.
- Air Sealing: Gaps and cracks in the roof deck or around penetrations can allow conditioned air to escape or unconditioned air to enter, significantly impacting energy efficiency. Thorough air sealing is vital.
- Ventilation: While less common in fully adhered BUR systems compared to vented attics, some low-slope roof designs benefit from specific ventilation strategies to manage heat and moisture.
- System Integration: The performance of the BUR system is interconnected with the building’s HVAC system. A more energy-efficient roof can allow for smaller, less expensive HVAC equipment.
The thermal performance of a built-up roofing system is a result of the combined properties of all its components working together. It’s not just about the top layer or the insulation; it’s about how the entire assembly manages heat and moisture flow throughout the year. A holistic approach to design and installation is necessary to achieve optimal energy efficiency and long-term building comfort.
Wrapping Up Your Built-Up Roofing System
So, we’ve gone through the layers and layers that make up a built-up roofing system. It’s pretty involved, right? From the deck all the way up to the final surfacing, each part plays its role in keeping your building protected. Understanding these components, how they work together, and what goes into installing them correctly is key. Whether you’re dealing with a commercial building or a multi-family home, a well-constructed BUR system offers solid protection. Just remember, proper installation and a bit of maintenance go a long way in making sure your roof does its job for years to come.
Frequently Asked Questions
What exactly is a built-up roof?
A built-up roof, often called a BUR, is a type of flat or low-sloped roof made by layering materials. Think of it like a sandwich with many thin layers of stuff stuck together. It’s made by repeatedly adding layers of asphalt and reinforcing materials, like felt paper. The top layer is usually covered with gravel or a special sheet to protect it.
What are the main parts of a built-up roof system?
A BUR system has a few key parts. First, there’s the roof deck, which is the solid base. Then come multiple layers of asphalt and reinforcing felt. These layers create a strong, waterproof barrier. Finally, there’s a top layer, often gravel or a ‘cap sheet,’ that shields the roof from the sun and weather.
Why does a built-up roof have so many layers?
Having many layers is super important for BUR roofs! Each layer of asphalt and felt adds strength and helps waterproof the roof. If one tiny part of one layer were to get damaged, the other layers underneath would still help keep water out. This makes the roof very reliable and less likely to leak.
How is a built-up roof different from other flat roof types?
Unlike some other flat roofs that use one big sheet (like EPDM or TPO), a BUR roof is built up from many smaller pieces layered together. This traditional method is known for its toughness and ability to handle foot traffic well, which is common on commercial buildings. Other systems might be quicker to install but have different strengths.
What kind of materials are used to make a built-up roof?
The main ingredients are asphalt and reinforcing materials called felts. The asphalt acts like glue, sticking everything together and making it waterproof. The felts, which are like strong paper or fabric, add strength to the layers. The top layer can be small stones (gravel) or a special protective sheet.
How long do built-up roofs usually last?
Built-up roofs are known for being tough and lasting a long time. With good installation and regular care, they can often last for 15 to 30 years, and sometimes even longer. Their layered structure helps them stand up to tough weather over many years.
Are built-up roofs good for all types of buildings?
BUR systems are best suited for buildings with flat or gently sloped roofs, which are common for commercial buildings, factories, and apartment complexes. They aren’t typically used on houses with steep roofs because of how they are constructed and how they shed water.
What are the downsides of built-up roofing?
One main thing to consider is that BUR roofs can be quite heavy because of all the asphalt and gravel. Also, putting them on takes a lot of work and time, meaning it can be more labor-intensive than some newer roofing types. In very cold weather, the asphalt can sometimes become a bit stiff.
