Modified Bitumen Roof
Updated: Feb 11, 2020
Modified Bitumen is the name of a popular flat roofing material that has been time tested and proven effective. Many people even claim that this is the best roofing system around today.
Bitumen is a name for a compound in asphalt. For the purposes of this article the terms bitumen and asphalt will be interchangeable.
Someone discovered that bitumen could be modified by mixing it with rubber or plastic and that this would increase the elasticity and resistance to extreme temperatures of the asphalt. They then began creating 3ft wide rolls of modified asphalt (mixed with rubber or plastic), with a polyester or fiberglass mesh reinforcement embedded. These rolls became known as modified bitumen.
There are 2 types of modified bitumen rolls.
APP = these are the rolls made out of asphalt that was mixed with plastic
SBS = these are the rolls made of asphalt that was mixed with rubber.
Both APP and SBS are time tested and proven and although it is debated which is superior there is no conclusive evidence one way or another and for the most part they can both be used in th same circumstances.
Modified bitumen is a phenomenal system for use in cities. In general buildings in cities have a very hard time with their roofs. The reasons are.
1.Buildings in cities can be many stories high. It can be very difficult to get your roofing material all the way to the top.
2. In addition to telephone wires trees and other things that can interfere, buildings in the city generally have lots of sidewalk traffic and very little parking this makes it hard to have the material lifted to the top using a crane or a boom lift.
3. Buildings in a city generally experience lots of traffic on their rooftop, whether from tenants using it as a balcony to relax on, or from maintenance men taking care of the HVAC units, a roof in the city is sure to experience lots of foot traffic. Many rooftops can easily be damaged or punctured from foot traffic, from chair legs, or from a maintenance man stepping on a nail, there are countless ways for your roof to be damaged when it is located in a city.
4. Usually building in a city are constantly undergoing change, a new tenant moves in and makes changes or a plumber or HVAC worker doing new installations, it is very common for new penetrations to be made in the roof to run wires and pipes and ducts into the building and if not sealed correctly they will leak.
5. Buildings in cities are loaded with penetrations from pipes, exhausts, HVAC units, wires and who knows what else. Because when laying out roofing material every time a roll hits a penetration. It needs to be stopped and worked around. This makes the job expensive. This type of work is known as detail work and in industry terms, detail work is the expensive work.
Modified bitumen is great for addressing these problems.
1. unlike other roofing materials modified bitumen comes in small rolls of only 3 feet wide. This makes it easy to carry up in staircases or in elevators.
2. unlike other roofing materials modified bitumen comes in small rolls of only 3 feet wide. This makes it easy to carry up in staircases or in elevators.
3. Modified bitumen is one of the most durable of all roofing materials (if no the most durable). It is the thickest roofing material and if traffic is a problem it can be installed in multiple layers to make it even more thicker and durable. Also it can be installed with granules embedded on top that help protect the rolls from wear and tear.
4. Modified bitumen is the easiest of all roofing materials to repair. It is compatible with all roofing mastics and tars, and any handyman or DIYer can easily repair it themselves using KARNAK/tar sold at Home Depot. Also because it is such a common roofing material all roofers should be familiar with how to repair it. Also unlike other material which can be damaged if they are repaired incorrectly, modified bitumen can be repaired temporarily by the person who cuts a whole to install pipes or wires and then later be revisited by a roofer to permanently fix it. TPO or EPDM can be permanently damaged if the incorrect material is used to repair it.
5. Because modified bitumen rolls are so small they are much easier to maneuver around existing penetrations on the roof. This makes the job cheaper and more likely to be done correctly.
Although modified bitumen originated as a material that was torched down it now can be installed in three ways
1. TORCHING = first the rolls are placed in position on the roof. Then a propane tank and torch are used to heat up the roll and melt the bottom layer of asphalt. While the torcher is heating up the roll he slowly unrolls it by either pushing it with his foot or using a metal cane. This results in heat welded seams that have a bead of molten asphalt oozing out. The benefit of torching is that this is the cheapest method of installation. The negatives are that using an open flame on a building is dangerous and has resulted in fires, and that if the installer is not a professional it is very easy for him to accidentally underheat or overheat the roll which will result in early failure of the roof system. Usually 2 or three plys of modified bitumen are installed, a base sheet/ply a mid sheet and a cap sheet. When only 2 layers are used it is just a base and a cap, and rarely only one layer will be installed, just a cap sheet, to save money.
1. This system is cheap because adhesives are not used to attach the membrane and the price of propane is comparatively inexpensive. Also the equipment needs to install this system is very minimal.
2. Because the equipment needed is very basic and inexpensive this is a very popular system for new roofing companies who do not have lots of money to spend on tools. Almost all companies offer this roof system as an option.
3.This system can be installed in any temperature.
4. Like all modified bitumen systems this system is durable and not easily punctured
5. When installed with more than one ply this system is redundant reducing the likelihood of a leak.
1. This system is dangerous because it requires an open flame to be pointed at your building. There have been many occurrences of fires as a result. Using an experienced contractor who follows safety protocol and trains his employees to do the same will greatly reduce the risk. Also in some states using this system on a roof with a wood deck is illegal. in other states if your roof deck is wood then a fire barrier is required in between the wood and the torch such as fireproof insulation.
2. Because the price of this system is so cheap and the equipment is so basic many fly by night/shady companies install this system without the correct knowledge, training or insurance. When you inevitably get a leak as a result of using an inexperienced company and try to call them back to make good on their warranty, most of the time they are no where to be found.
3. Most roofing companies insurance specifically exclude torching from their coverage. in some cases the owner of the company is not aware of this and in other cases they are aware but they choose to mislead you. If you choose a torching system be sure to specifically check the roofers insurance to make sure it includes torching (do not just rely on their honesty).
4. This system requires a very skilled crew to install it correctly. If a roofer is inexperienced, instead of fully heating/melting the rolls and delivering you a fully adhered system that has no air pockets or channels for water to travel, they may only spot heat the rolls with will give you an end product that is only adhered in certain spots but can allow water and air to travel under it.
5. Like all modified bitumen systems this system has lots of seams which can potentially open and cause leaks
2. COLD PROCESS = This type of installation relies on cold asphaltic adhesives to adhere the modified bitumen rolls to the roof. The adhesive is spread using a squeegee and the rolls are unrolled onto of it.
This is more expensive than torching because there is the additional cost of the adhesive. However this is a safer more reliable installation.
1. Because this system is installed by spreading glue it is easy to visually check that there are no spots missing glue before they roll out the sheets. This means that it is easier to instal this system correctly.
2. It is a safe system to install.
3. Like all modified bitumen systems this system is durable and not easily punctured
4. When installed with more than one ply this system is redundant reducing the likelihood of a leak.
1. Because this system has the added expense of glue it is more expensive than a torch system.
2. Because this system is installed with black adhesive that is sticky it can be very messy and the glue can quickly spread on feet all over the roof. If you purchase a white roof it is not uncommon for it to have black footsteps all over it. I suggest that when doing a cold applied roof it is better either to choose black so that the glue blends in or to coat the roof in aluminum paint after the glue dries to cover it up.
3. This system can only be installed when the weather is above 40 degrees Fahrenheit otherwise the adhesives will not perform properly.
4.Like all modified bitumen systems this system has lots of seams which can potentially open and cause leaks
3. PEEL AND STICK / SELF ADHERED = as its name implies, peel and stick modified bitumen has a layer of adhesive on the back of the roll. The protective layer of plastic is peeled off and the roll is adhered to the roof using pressure from a weighted roller. Peel and stick modified bitumen roofing is relatively new and doesn't have a long track record.
1. Because this system is peel and stick it is pretty easy to install correctly.
2. It is safe to install
3. It is pretty cheap to install
4.Like all modified bitumen systems this system is durable and not easily punctured.
5.When installed with more than one ply this system is redundant reducing the likelihood of a leak.
1. This system can only be installed when the weather is above 40 degrees Fahrenheit otherwise the sticky part on the back of the sheet will not perform.
2. This system is not good for roofs that are flat or close to it. When installing a peel and stick it is preferable that the roof has a good pitch towards the drainage areas. The reason being that peel and stick seams are not as strong as torched seams or as glued seams.
3. This is a relatively new system and has not been time tested. Some companies have had issues with the adhesive not working correctly.
4. Like all modified bitumen systems this system has lots of seams which can potentially open and cause leaks
The best and most expensive modified bitumen systems have three plys of material installed, a base sheet/ply a mid sheet and a cap sheet. When only 2 layers are used it is just a base and a cap, and rarely only one layer will be installed, just a cap sheet, to save money.
Now if you are reading this article in an attempt to decide what system is best for your building I have good news and bad news. the good news is that all of the above systems can last long, 10-20 years, and protect your building from water. The bad news is that all of the above systems can also fail prematurely and be a waste of money. How can this be?? In the industry we have a saying, "its not the type of roof systems that you purchase but rather the people that you hire to installl the system."
However taking all that into account I will list some tips on certain situations where it may be better to choose on system over another.
1. Because peel and stick is new and not time tested I would avoid it if other options are available.
Also some companies have had issues with the stickiness On the back of the rolls not functioning correctly and seams opening up.
2. If your roof is wood deck is wood you should consider cold applied/glue down modified bitumen for safety reasons.
3. If your roof deck is metal or concrete you should consider torch down modified bitumen for its cost savings. (however make sure the company is reputable and in business for a long time under the same company name, not constantly changing the company name to avoid lawsuits).
4. If it is winter season and you live in an area that has cold winters I suggest torch down modified bitumen the reason being because both peel and stick and cold applied/glue down require the weather to be above 40F for the adhesives to work correctly.
5. Torch down should always be the cheapest to install because of the savings on material. so if money savings is your ultimate goal torch down is the way to go.
With all this in mind the most important thing to remember is that "its not the type of roof systems that you purchase but rather the people that you hire to installl the system.". When all is said and done you want a company who is experienced installing the product that you purchase and who is going to backup their work by honoring their warranties.
If possible it is always better to get a manufacturer warranty on a job, this means a warranty from the company who makes the roofing material not from the roofer himself, and I'm talking about a labor and material warranty no dollar limit, not just a material warranty because material warranties are worthless, (what good is getting free material if you need to pay to have it installed). The reason being that manufacturer are much more likely to be in business in 10 years from now and are also more likely to answer the phone and honor the claim.
Here at Roofing Team Inc we are capable and experienced installing certified roofs with warranties from all of the main roofing manufacturers. Including GAF, Firestone, Soprema, Mulehide, and more.