Built-Up Roof Vs. Modified Bitumen: Which One Is the Best for Commercial Building

Posted on October 13th, 2021 by Applied Roofing Services

Built-up and modified bitumen roof systems are usually designed for low slope or flat roof structures. While both can withstand harsh weather conditions and harmful UV rays, the two are different in terms of design, application, advantages, and life expectancy.

Read on to learn more about these roofing systems and evaluate the best option for your commercial building.
built up roof

Built-Up Roof Systems

Also known as tar and gravel roofs, built-up roof systems are made of alternating layers of bitumen (asphalt) and reinforcing fabrics. The top layer of the roof is finished with stone or gravel coating to create a continuous sealed surface.

Modified Bitumen Roof

This is an asphalt-based roofing system designed with two layers, namely a base sheet and a cap sheet. While the cap sheet is torched down, self-adhered, or cold-adhered, the base sheet is self-adhered to the roofing substrate.

Modified bitumen BUR can be of two types,

  • Styrene-Butadiene-Styrene (SBS)– Being elastomeric, it can stretch to provide greater flexibility (contraction and extraction capabilities).
  • Atactic Polypropylene (APP) – Being plastomeric (made flexible with elastic plastic) means it can resist harmful UV rays, improving your roof’s stability with time.

Pros and Cons of Flat-roofing Systems

There are 3 types of flat roofing systems for commercial buildings – modified bitumen roofs, single-ply roofs, and built-up roofs. Therefore, it is essential to evaluate the advantages and disadvantages of each roof type to make the right decision for you.

Roofing SystemProsCons
Built-Up Roof
  • Fire resistant
  • Looks appealing
  • Cost-effective
  • Very heavy
  • Requires professional installation
  • Gravel can clog scuppers and gutters
Modified Bitumen Roof
  • DIY installation is possible
  • Energy efficient
  • Inexpensive
  • Not tear-resistant
  • The torch-down application creates a fire hazard
Single-Ply Roof
  • Tear and scuff resistant
  •  Easy to install and repair


  • Expensive
  • Susceptible to punctures

Built-Up Roof System and Other Options for a Commercial Roof

There are two main types of built-up roofing systems, including:

  1. Modified Bitumen BUR

Made of rubber and asphalt, this roof is finished with gravel on top. The modified BUR can be installed on the roof deck using adhesives.

Modified bitumen BUR roofs have three layers, including:

Base Asphalt Layer

This acts as a primary waterproof layer and is modified with synthetic rubber to create a uniform matrix. While strengthening the asphalt, the synthetic rubber improves puncture resistance and elasticity.

Ply Sheets

These sheets can be made of plastic core materials, felt, reinforced fabric, polyester, or fiberglass. They offer weather resistance, stability, and tensile strength to the final finished roofing structure.

Top Surface

While protecting the lower layers from rain and debris, the top surface holds and releases sunlight to prevent moisture and heat damage.

  1. Ballast Roofing

A ballasted roof has a loose-laid bottom-most sheet on the roof deck that separates the roof membrane from the decking material. Though not adhered or anchored, the top layer of the roof is ballasted with gravel stones to keep the roof membranes in position.

In order to prevent excess movement, roof membranes are fastened at certain places on the deck. While providing an aesthetically pleasing look, the ballast roof remains durable by contracting and expanding during cold and hot weather. These roofs are also fire-resistant, energy-efficient, and easy to repair.

What Are Built-Up Roof Systems Made of?

A built-up roof system is made of three layers:

Base Sheet

The asphalt in the base sheet is fastened to the insulation or roof deck to prevent blisters (soft bubbles) and allow vapor movement. You can use industry-standard fully adhering base sheets to prevent the membrane from tearing.

Roofing Felts

These are reinforcing fabrics (organic mats or fiberglass) that increase the roof’s durability while resisting thermal shock and moisture.

Surface Layer

The surface layer with stone, gravel, or mineral granules is finished with aluminum roof coatings, hot asphalt, or elastomeric sealants to withstand dampness and UV rays.

Built-Up Roof System – Repair and Maintenance

Generally, BUR roof systems are prone to the following defects:

  • Cracks – Small cracks may form on the roof surface due to asphalt shrinking.
  • Blisters – Moisture can cause soft bubbles in the roof membrane.
  • Damages – Thermal expansion or detached insulation can damage the roof.

Regular roof maintenance by a professional roofing contractor can help detect these repairs before they aggravate. This way, you can fix the repairs on time and maintain your roof in top condition.

Built-Up or Modified Bitumen: Which Is Better?

While both roof types have advantages and disadvantages, deciding which one is the best for your commercial property depends on your requirements, the building’s condition, and your roof’s pitch.

Therefore, consider hiring a commercial roofing contractor to determine the best roof for your building.

Why Choose Applied Roofing as Your Commercial Roofing Contractor?

With over two decades of experience in the roofing industry, our team at Applied Roofing Services specializes in commercial flat roofing systems, low slope roofs, and green roofing solutions. All our roofing systems are of high quality, ensuring low maintenance and durability. We also have experienced and highly trained roofing professionals who can install your commercial roof in an efficient and non-intrusive manner.

If you are looking for the best commercial roofing contractor in California for installation, repair, and maintenance services, contact Applied Roofing Services today at 714-632-8418 or get a quote online.

About Applied Roofing Services

Applied Roofing Services is a full service roofing company located in CA. We offer durable and high quality residential and commercial flat roofing. We provide roof installation as well as roof repair services, roof maintenance and inspection services. We specialize in low slope roofs, energy efficient, zero maintenance, and green roofing. We have 20+ years of experience in the roofing industry.

Friendly Roofing

How to protect your roofing investment by selecting the right roofing contractor?



Orange County Office:

1961 N. Main St.
Orange, CA. 92865
Phone: 714-632-8418 or
(800) 895-9589

Get Directions

Los Angeles Office:

1055 West 7th Street
33rd Floor Penthouse
Los Angeles, CA 90017
Phone: 213-255-3677

Get Directions


San Bernardino Office:

8333 Foothill Blvd
PMB # 411
Rancho Cucamonga CA 91730
Phone: 909-361-6119

Get Directions


Need To Know More?
Download our E-Brochure

Customer Review...

ARS has been my only foam roofing contractor nearly 15 years. There service is excellent and price competitive. I would recommend them highly

Dave A

crrc energystar bbb bestroof