Flat roofs can be both a blessing and a curse.
They’re everywhere: on commercial buildings, warehouses, schools, even modern homes. But for roofers, flat roofs come with their own special set of challenges. Tricky drainage, tough weatherproofing, and the need for materials that need to hold up under serious wear and tear.
That’s exactly why many roofers love using modified bitumen roofing for flat roofs. It can be a pain to figure out at first, but once you have the installation mastered, it solves all your flat roof issues.
Whether you call it mod bit, mod-bit, MB, or “a real bitumen to install,” modified bitumen is a known go-to. Perfect for roofing contractors who want something durable, reliable, and relatively easy to work with on flat or low-slope roofs.
Maybe you’re new to roofing and just building out your business. Or maybe you’ve been roofing a long time, but you’ve never been confident on how to tackle flat roofs. Whatever the case, understanding this system can help you take on more complex jobs and do ‘em right the first time. Read on.
What is “mod bit” or modified bitumen?
Modified bitumen is a type of asphalt-based roofing, reinforced with rubber or plastic polymers to make it more flexible and weather-resistant. Think of it as the next evolution of traditional asphalt roofing. It’s tougher, longer-lasting, and better suited for flat or low-slope applications.
It’s been around since the 1960s, first gaining traction in Europe and later becoming a U.S. staple by the 70s. These days, it’s still a top pick for commercial and residential flat roofs.
How to pronounce bitumen
Bitumen’s a funny looking word, and everyone’s first question is: how the f**k do you say that? So let’s clear up the pronunciation.
You’ll hear a lot of people say it differently. But technically, it’s “bit-ew-min” (rhymes with “litch-oo-min”). Only major difference is on whether you put the emphasis on the first syllable or the second one, but same basic word either way. You can hear the word pronounced in this YouTube video.
So if you’ve been wondering how to pronounce bitumen, there ya go! Now you can say it with confidence. And yeah, it does sound a “bit” like a curse word, so you can have a giggle if you want.
Where you’ll see mod bit used
- Commercial flat roofs
- Residential low-slope extensions and garages
- Roof decks and walkable surfaces
- Re-roofing projects (especially over old BUR systems)
‘Course, mod bit isn’t the only option for flat roofs. You’ll also run into:
- BUR (Built-Up Roofing): layers of hot tar and gravel… it’s heavy, messy, and smelly.
- EPDM (Rubber Membrane): flexible, great for hot climates, but pricier.
- PVC or TPO: lightweight and energy-efficient, but harder to repair.
Mod bit lands in a sweet spot. It’s relatively cost-effective, tough, and familiar for most crews. So it’ll make your customers happy, and your installers happy too.
How is modified bitumen installed?
One of the reasons mod bit roofing is so popular among roofers is due to how versatile it is. Lots of approaches you can take. There are a few different ways to install it depending on your crew, your tools, and your project’s needs:
Torch-down
This is the classic method. You heat the underside of the membrane with a torch as you roll it out, so it adheres right to the surface. It creates a watertight seal and strong seams, but also comes with fire risk (especially on older wooden buildings).
Hot-mopped
Similar to old-school BUR installation, this method uses hot asphalt to bond the layers together. It’s effective, but messy and requires extra safety gear. Not the most fun to install, but you might want to opt for this method to do the job right.
Cold-applied or self-adhered
This is a newer, more modern method of mod bit installation. No flames, no fumes — just peel, stick, and roll. Many new systems use adhesives or cold-applied coatings, which are safer and faster to install.
That said, buyer beware, and do extra product research before committing to self-adhering mod bit. Reviews wary, and some roofers consider this to be an inferior option: more the domain of DIYers or those trying to get the job done for cheap. So read reviews and make your own call on this one.
⚠️ Tip: Whichever method you use, make sure to inspect what’s underneath. Skipping that step to save time will come back to haunt you if there’s trapped moisture or rot in the deck.
Pros vs. cons of mod bit roof systems
Advantages of using modified bitumen
- Durable and long-lasting: When installed correctly, seams are just as strong as the membrane itself. That means fewer leaks and repairs needed. Hell yeah.
- Weather-resistant: Performs well in both freezing and sweltering conditions. It expands and contracts without cracking.
- Tear-resistant: Perfect for flat roofs that see foot traffic or act as decks.
- Energy-efficient: The top layer can be treated with reflective coatings (“cool roof” systems) to cut down on heat absorption.
- Easy to repair: Leaks or punctures are usually pretty easy to spot and patch.
- Environmentally friendly: Many systems today are recyclable or made with recycled content. We love a sustainable roofing system.
Drawbacks of using modified bitumen
- Torch-down risks: Open-flame installations require experience and caution, especially on wood structures. Seriously, be extra careful here.
- Heat absorption: Without proper insulation or reflective coating, mod bit can run hot. Great for those who like it hot. For others, might be dicey.
- Scuffing and surface wear: High foot traffic can leave marks or wear down the surface over time. It’s fine in most cases, but if this is going to be a patio for a homeowner, just be sure to give ‘em the disclaimer so there are no surprises down the line.
- Limited lifespan: Depending on location and other external factors, expect 20 to 30 years of service with good maintenance. Not bad at all, but not forever.
Make the right choices for your roofing business
As a roofing business owner, every decision matters: what materials you use, how you train your crew, and how efficiently you run your operation. That’s why it’s smart you’re here, reading up on it before jumping in with both feet.
Modified bitumen roofing is a dependable, proven system that’ll help you take on more flat roof work and feel great about it. Knowing your materials, and choosing the right ones for the right jobs, is an important piece of the puzzle.
The other piece is how smoothly you run your business… and that’s where Roofr can help.
Want to set yourself up for success? Here’s another great choice you can make for your roofing business early on: use Roofr. It’s easy to get started, and we’ve got tons of resources to help you onboard, streamline your pipeline, and grow your business fast.
You’ll save time, improve your service quality, and earn the trust of your customers. And make your life a hell of a lot easier.