TPO vs. Modified Bitumen Roofing: What You Need to Know

Jun 5, 2023

WRITTEN BY:

Moises V.

CATEGORY:

Uncategorized

POSTED ON:

June 5, 2023

UPDATED ON:

October 13, 2023

Got Questions?

Choosing a high-performing roofing system ensures your building’s interior is well-insulated and protected from the elements. It’s a critical step in the construction process that can determine the longevity of your building’s structure.

There are many roofing systems to choose from, among which are thermoplastic polyolefin (TPO) and modified bitumen. Both offer benefits in terms of durability, weather resistance, and ease of installation. 

Understanding what sets one apart from the other can help you make an informed decision. Once you’ve made up your mind, it’s essential to have your roofing installed by licensed professionals. If you live in Minnesota, contact Viking Contractors, LLC, for all your roofing inquiries!

What is TPO?

Worker applies pvc membrane roller on roof very carefully. Correct welding with hand-welder, corner.

Thermoplastic polyolefin (TPO) is a single-ply, heat-reflective, and energy-efficient roofing material. Single-ply means that you install a single sheet of TPO for full coverage. 

The TPO sheet has three bonded layers: a thermoplastic polyolefin base layer, a polyester-reinforced fabric center layer, and a thermoplastic polyolefin top layer.

It came in large rolls welded together and laid atop the roof deck. And while it’s common in large, flat or low-sloped industrial or commercial buildings, it’s also used in residential buildings, which can benefit from its structural advantages.

TPO is both heat-reflective and energy-efficient thanks to its distinctive light colors: white, light gray, and tan. These colors reflect heat instead of absorbing it, allowing for cooler interior temperatures. This saves the energy that would be otherwise spent by your HVAC system cooling your building’s interior.

However, note that TPO’s distinctive light colors are prone to getting dirty, depending on your location’s climate and environmental factors. A dirty, low-sloped TPO roof can be an eyesore to some people.

What is Modified Bitumen?

Waterproofing Works. Construction worker applying SBS Modified Bitumen Roll Sheet over a Concrete Bridge Deck with Butane Gas Blow Torch

Modified bitumen is a multi-ply roofing material made of asphalt mixed with polymers and reinforced with fiberglass or polyester. 

A modified bitumen roofing system usually consists of a base and cap layer. Depending on your roof’s condition and installation method, you can enhance it further with other layers, such as a reinforcing fabric layer and an asphalt emulsion base coat. This makes it somewhat similar to a built-up roofing system.

Modified bitumen roofs can adapt to different temperatures and building movements. They’re also resistant to weathering, tears, and fire. You can install it using many methods, too, including heat welding and mechanical attachment.

It also stands out for being coatable with granules and reflective materials, allowing you to improve its appearance and performance as you see fit. It’s most common in flat and low-sloped roofs. 

However, without a reflective coating, modified bitumen’s dark color attracts and absorbs heat, increasing your cooling costs.

TPO vs. Modified Bitumen: Comparative Analysis

Below, we’ll compare both roofing systems on the basis of cost, installation, durability, energy efficiency, and lifespan to help you decide what suits your situation best.

Cost

Your budget is critical in determining which roofing system you’ll opt for. While both roofing systems are excellent in terms of durability, they vary in cost significantly.

Modified bitumen is more expensive than TPO materials-wise. It’s a by-product of crude oil refining, so crude oil’s price and the availability and efficiency of crude oil refineries influence its price. It’s also a heavy, viscous material that requires special transportation methods. 

TPO, on the other hand, is cheaper because a single layer of thermoplastic makes it up. It also requires less expertise and specialized equipment. 

Cost-effective investment in your own home.

Modified bitumen has a slightly lower upfront cost, but TPO has a lower total cost over the roof’s life due to the differences in labor, maintenance, and installation costs.

These costs vary from one region and contractor to another, though. Your roof’s size and complexity largely influence them too. Mind that competitive pricing for TPO installation has emerged due to its rising popularity, so you may find sweeter deals depending on your location.

A modified bitumen roof will cost you $4 to $7.5 per square foot, while a TPO roof will cost you $4 to $10. These are U.S. market averages, by the way!

Installation

TPO is easier and faster to install. It’s a single-ply roofing material that requires less labor and equipment. 

TPO comes in large rolls; you can install it using one of the following methods:

  • Apply an adhesive to the membrane’s underside and the roof deck.
  • Fasten it to the roof deck using screws or plates, then heat-weld the membrane at the seams to create a water-tight seal. 
  • Ballast it by flashing the edges and penetrations and covering it with gravel.

All these installation methods require minimal expertise, hence their lower cost. 

Installation of modified bitumen can be done using the following:

  • The self-adhesion method, where you peel off a protective film from the back of the modified bitumen sheets and stick them to the roof deck or insulation, then heat-weld the seams.
  • The heat adhesive method where you use a torch to melt the bitumen and mold it to the roof.
  • The cold adhesive method is where you glue the sheets using a liquid adhesive without heating.

Since installing modified bitumen can sometimes involve the use of heat sources, it tends to be costly and potentially dangerous. The heat torch also poses a fire hazard, so only professionals should handle it.

Durability

Aside from costs, durability is what you’re probably most concerned about; you want a roofing system that can protect your building and last long.

TPO is the newer and more flexible roofing system that can adapt to different roof shapes and sizes. It’s more resistant to UV rays, mold, and environmental pollutants. 

However, TPO isn’t as resistant to heavy foot traffic and tears, but its seams are heat welded to create a water-tight surface to prevent water infiltration. It isn’t very resistant to fire and heat, either. It may degrade faster in extreme heat, so you’re better off with an alternative if you live in such areas. 

The silver lining is that it requires less repair and maintenance since it’s less prone to cracking, blistering, and peeling.

Modified bitumen is a different story. It comes in two types: styrene butadiene styrene (SBS), a rubber-like polymer, and atactic polypropylene (APP), a plastic-like polymer.

SBS and APP have similar characteristics in terms of elasticity and flexibility, but APP is better suited for high-temperature settings, while SBS performs better in low-temperature locations. 

SBS is also more resistant to water and hail than APP, while APP can withstand fire and wind better. They can also handle high foot traffic, tears, and punctures better than TPO.

However, they can crack, blister, and peel over time. So, maintenance can be a concern; you may have to inspect and repair them more often than TPO.

Energy Efficiency

TPO roofs are more energy efficient than modified bitumen ones. TPO’s distinctive light color and UV-resistant, reflective surface allow it to reflect sunlight and heat instead of absorbing it, preventing your building’s interior from warming up and saving you energy costs otherwise spent in cooling.

Modified bitumen is multi-layered and primarily made of asphalt. Its darker color attracts and absorbs heat, which is especially concerning in hotter climates. The heat it retains can radiate into your building’s interior and warm it up, leading to increased energy costs for your HVAC system.

Lifespan

If you properly install and maintain them, TPO roofs can last 20 to 30 years.

Modified bitumen roofs usually last around 20 years, but you’ll have to consider maintenance costs for their upkeep. If you skimp out on regularly inspecting and repairing them, they can last much shorter than that.

The bottom line is that modified bitumen is ideal as a cost-effective roofing option initially, but it requires regular maintenance and repairs in the long run. And TPO, while expensive to install initially and fairly durable, isn’t as resistant to fires and harsh weather conditions. 

Conclusion

The choice of roofing material for your next retrofitting project largely depends on your situation, budget, and existing roof condition. Both TPO and modified bitumens have contextual advantages and disadvantages that can make it challenging to determine which one is better than the other.

TPO is more energy-efficient, modern, and easier to install, but it’s less resistant to harsher weather conditions than modified bitumen. And while modified bitumen can withstand environmental damage better, it’s more prone to cracking and blistering, costing you more to maintain in the long run.

We recommend contacting a professional who can assess your situation and provide you with expert advice when planning to start a roofing project. At Viking Contractors, your satisfaction is our responsibility. Contact us today for your free inspection!

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